any illness, impairment, or abnormal condition that affects primarily infants and children—i.e., those in the age span that begins with the fetus and extends through adolescence.

Childhood is a period typified by change, both in the child and in the immediate environment. Changes in the child related to growth and development are so striking that it is almost as if the child were a series of distinct yet related individuals passing through infancy, childhood, and adolescence. Changes in the environment occur as the surroundings and contacts of a totally dependent infant become those of a progressively more independent child and adolescent. Health and disease during the period from conception to adolescence must be understood against this backdrop of changes.

Although, for the most part, the diseases of childhood are similar to those of the adult, there are several important differences. For example, certain specific disorders, such as precocious puberty, are unique to children; others, such as acute nephritis—inflammation of the kidney—are common in children and infrequent in adults. At the same time, some diseases that are common in adults are infrequent in children. These include essential hypertension (high blood pressure of unknown cause) and gout. Finally, a major segment of pediatric care concerns the treatment and prevention of congenital anomalies, both functional and structural.

Apart from variations in disease due to differences between children and adults, certain other features of diseases in children need to be emphasized. Infectious disorders are prevalent and remain a leading cause of death, although individual illnesses are often mild and of minor consequence. Most instances of the common communicable diseases, such as measles, chicken pox, and mumps, are encountered in childhood. Disorders of nutrition, still of great concern, especially but not exclusively in developing countries, are of extreme importance to the growing and developing child. The unique nutritional requirements of children make them unusually susceptible to deficiency states: vitamin-D deficiency causes rickets, a common disorder of children in developing countries, and only rarely causes any disease in adults. The major environmental hazards that endanger the health of young children are either unavoidable, as in air pollution, or accidental, as in poisoning and in traffic injuries. Older children, especially adolescents, are exposed, as are adults, to environmental hazards that they deliberately seek, such as cigarette smoking and the use of alcohol and other drugs.

This article reviews the scope of diseases that affect children, with particular emphasis on the ways in which the unique attributes of the growing child and special aspects of his environment serve to modify the course, effects, and treatment of particular diseases.

Diagnosis of the diseases of childhood involves special considerations and techniques; for example, in evaluating genetic disorders, not only the patient but his entire family may need to be examined. Inapparent environmental causes of diseases, such as poisonings, must be considered and investigated thoroughly, by methods that at times resemble those of a detective. Diseases of the fetus may derive directly from disorders of the mother (obstetrics and gynecology) or may be caused by drugs administered to her. Diagnostic techniques have been developed that permit sophisticated examination of the fetus despite its apparent inaccessibility. The withdrawal of a small amount of the amniotic fluid that surrounds the fetus permits examination of fetal cells as well as the fluid itself. Chromosomal and biochemical studies at various stages of development may help to anticipate problems in the postnatal period; they may indicate the need for immediate treatment of the fetus by such techniques as blood transfusion; or they may lead to the decision to terminate pregnancy because serious, untreatable disease has been recognized. Other specialized techniques permit examination of the fetus by X ray and ultrasound, and by electrocardiography and electroencephalography (methods for observing and recording the electrical activity of the heart and the brain, respectively). Fetal blood can be obtained for analysis, and certain techniques permit direct viewing of the fetus.

In examination of the infant, inaccessibility is no special problem, but his small size and limited ability to communicate require special techniques and skills. Of even more importance, however, is the fact that adult norms cannot be applied to younger age groups. Pediatric (pediatrics) diagnosis requires knowledge of each stage of development, with regard not only to body size but also to body proportions, sexual development, the development and function of organs, biochemical composition of the body fluids, and the activity of enzymes. The development of psychological and intellectual function is equally complex and requires special understanding. Since the various periods of growth and development (child development) differ so markedly from one another, they are divided for convenience into the following stages: intrauterine (the period before birth), neonatal (first four weeks), infant (first year), preschool (one to five years), early school (six to 10 years for girls, six to 12 for boys), prepubescent (10 to 12 for girls, 12 to 14 for boys), and adolescent (12 to 18 for girls, 14 to 20 for boys). Only if appropriate norms are established for each stage of development can the child's condition be adequately evaluated and the results of diagnostic tests properly interpreted. Thus, it is of no concern if a 12-month-old infant is unable to walk alone, although some infants are able to do so at nine months of age. The crucial question is at what age one becomes concerned if a developmental milestone has not been reached. Five-year-old boys average 44 pounds (20 kilograms) in weight but may vary from 33 to 53 pounds (15 to 24 kilograms). The hemoglobin level that is of no concern in the three-month-old infant may reflect a serious state of anemia in the older child. The blood levels of certain enzymes and minerals differ markedly in the rapidly growing child from those in the late adolescent, whose growth is almost complete. Failure of a 15-year-old girl to have achieved menarche (the beginning of menstruation) may be indicative of no abnormality in sexual development but requires careful evaluation.

Treatment of childhood disease requires similar considerations with regard to various stages of growth and development. Variation in drug dosage, for example, is based not only on body size but also on the distribution of the drug within the body, its rate of metabolism, and its rate of excretion, all of which change during various stages of development. The inability of infants and small children to swallow pills and capsules necessitates the use of other forms and alternate routes of administration. Drug toxicity of importance at one stage of development may be of no concern at another; for example, the commonly used antibiotic tetracycline is best avoided in treatment of the child younger than age 10 because it is deposited in teeth, in which enamel is also being deposited, and stains them. When permanent teeth are fully formed, the deposition of tetracycline no longer occurs. The delayed consequences of certain forms of treatment, especially with radioactive isotopes—substances that give off radiation in the process of breaking down into other substances—might be of no consequence in the case of an elderly person with a life expectancy of 10 or 20 years but might deter a physician from the use of such treatments for the infant with his whole life in front of him. Finally, the nutritional requirements of the growing child must be considered when treatment of disease requires modification of the diet or administration of drugs that may affect the absorption or metabolism of essential nutrients.

The outlook for recovery from diseases in children is often better than it is for adults, since the child's additional capacity of growth may counteract the adverse influences of disease. The bone fracture that results in permanent deformity in the adult, for example, may heal with complete structural normality in the child, as continued growth results in remodeling and reshaping of the bone. Ultimately, the infant who has one kidney removed because of infection or tumour most likely will have entirely normal renal (kidney) function because the remaining kidney will increase its size and functional capacity with growth. In contrast, removal of one kidney in the adult usually results in a residual functional capacity equal to 70 to 75 percent of that of two normal kidneys.

Thus, being in a period of rapid growth and development may favourably affect the child's recovery in the course of a disease. The converse may also be true, however. The rapidly growing and maturing central nervous system, for example, is particularly susceptible to injury during the first two or three years of life; also, adolescents may react unfavourably to psychological stresses that are tolerated readily by more mature individuals.

In the general consideration of childhood diseases, a final aspect that merits emphasis is the role of prevention. The major factors responsible for the decline in infant and childhood mortality rates over the past decades have been the development and application of preventive measures. By the late 20th century, in most countries the death rate for infants under one year of age had decreased until it was scarcely more than a 10th of the rate in the 1930s. Socioeconomic factors—such as better maternal nutrition and obstetrical care and improved housing, water supplies, and sewage disposal—have been of prime importance in this decline, together with better hygiene at home, safer infant feeding techniques, and widespread immunization against common infectious diseases. In comparison to the favourable effect of these and other preventive measures, an increased capacity to treat diseases, even with such powerful tools as the antibiotic drugs, has had relatively little impact. In the developed countries, where the most common causes of childhood morbidity and mortality are accidents, prevention depends upon a willingness to design and modify communities and homes to make them safer for children. Just as important as the development of public health measures is their practical application; underutilization of established procedures and techniques for prevention of disease is a major health problem.

Disturbances in growth may be among the most striking consequences of disease in children. An obvious example of this effect is total growth failure, which is seen in almost every serious disease of infants and children. Local retardation or disturbance in growth patterns may be equally striking. Osteomyelitis, an infection of bone, may, for example, result in retardation or cessation of growth at that site, with subsequent severe asymmetry between the affected limb and its normal counterpart. Enlargement of the heart as a result of cardiac disease may cause gross distortion of the chest, as the growing ribs adapt to the abnormal shape of the heart.

Many differences in the manifestations of disease in children and adults can be ascribed to differences in anatomical structure and in biochemical, immunological, and physiological function. Less well understood are the consequences of differences in psychological function. In general, the younger the child, the more striking these differences are.

Not only is the child's body smaller than that of the adult, but it has different proportions; for example, the sitting height of the newborn infant represents about 70 percent of total body length. With rapid growth of the extremities, sitting height decreases to about 57 percent of the body length at three years of age and, finally, as growth proceeds more slowly, to the adult proportion of about 50 percent. Growth and development are not necessarily smooth, continuous processes. Weight and height increase rapidly in infancy and at puberty; for example, the head completes half its total growth in the first year of life, and by the age of two years the child has reached half his adult height. In addition to differences in proportion and size, there are marked differences in body composition between children and adults. As examples, in newborn infants muscle mass constitutes approximately 25 percent of total body weight, compared to 43 percent in adults. Total body water, which accounts for 90 percent of early fetal weight, represents 75 percent of body weight at birth, drops to about 60 percent by one year of age, and then declines gradually to reach the adult figure of 55 percent. The higher proportion of body water, due almost entirely to a relatively greater volume of fluid outside the cells, affects the response of the infant, particularly to disturbances in water balance.

There are many examples of differences in anatomical structure that affect manifestations of disease. In assessing the health of the infant with cardiac or pulmonary (lung) disease, the thinner chest wall, the relatively more horizontal position of the heart, and the more rapid cardiac and respiratory rates must be taken into account. The thin abdominal wall of the infant permits palpation—examination by touching with the fingers—of the kidneys, whereas in older subjects the kidneys usually can be felt only if they are abnormally large. In the infant, with the bones of the skull still not fused together, obstruction of the flow of cerebrospinal fluid may result in striking enlargement of the head, a condition referred to as hydrocephalus. In the older child, when the skull sutures have fused, such enlargement is not possible, and the manifestations of spinal-fluid obstruction are similar to those of the adult, including severe headache and visual difficulties as a result of increased intracranial pressure. The primary manifestation of mumps is a painful swelling of the parotid and other salivary glands. In adolescents, involvement of the testes or ovaries occurs only rarely, a phenomenon related in some way to the immaturity of these organs. In the adult, particularly in the male, severe sex-gland involvement is common.

Physiological differences between children and adults that cause differences in the manifestations of disease include all the various functional, endocrine, and metabolic features of the growing and maturing organism. A major characteristic in this regard is the limited ability of the infant to maintain homeostasis (a stable internal environment) during illness because of his greater metabolic and nutritive requirements. Moreover, most of the first year of life is characterized by immaturity of renal function, the capacity of the kidneys to respond to the stresses of disease being less than later in life. The baby with severe diarrhea, for example, cannot conserve water well enough and may become dehydrated. With any degree of stress, metabolic abnormalities are likely to be more severe in the infant than in the older child.

The liver of the newborn child also demonstrates certain features of immaturity. Of particular importance is its limited capacity to excrete bilirubin, a product of the breaking down of hemoglobin (the oxygen-carrying pigment of red blood cells). In certain conditions in which there is a rapid rate of destruction of red blood cells, the inability of the liver to excrete the added load of bilirubin may result in a large increase in the concentration of this substance in the blood; the bilirubin concentration, if high enough, can cause severe brain damage known as kernicterus. Since immaturity of the brain also contributes to the infant's increased susceptibility to this disorder, kernicterus is rarely encountered outside of the neonatal period, even in subjects with severe liver disease.

The ability of the young infant to metabolize and to excrete certain drugs is limited by the immaturity of the liver and of the kidney, and drug dosage must be adjusted accordingly.

The immunologic system of the body is responsible for the defense against disease. This highly complex system involves the production of antibodies (proteins that can recognize and attack specific infectious agents); the action of granulocytes and macrophages, cells that destroy infecting organisms by ingesting them (a process called phagocytosis); and the function of a variety of cellular mechanisms involving the complement system (complement is an enzyme-like substance in the blood). Antibody production in the infant is qualitatively and quantitatively different from that in the older child and adult. Although the differences in antibody response cannot be related specifically to differences in the capacity of the infant to withstand infection, they certainly must play some role. On the other hand, many of the clinical features of infectious disease occurring during the first two or three years of life appear to be related to the fact that these are infections occurring for the first time.

Another difference in immunologic response between children and adults is in the functioning of the reticuloendothelial system. This system, which is composed of the macrophages found in the lymph nodes, spleen, and other lymphatic tissues, is relatively more active in childhood. Since macrophages ingest infectious organisms, children with coryza or sore throats commonly have swollen lymph “glands” visible and palpable in the neck. Similarly, their tonsils and adenoids, which are lymphatic tissues, swell rapidly in response to mild infections.

Infectious diseases of the fetus are caused by many different types of organisms, including viruses, bacteria, spirochetes, and protozoa (e.g., toxoplasmosis). Most of these infections are the result of infection of the mother, the infectious agents being transmitted through the placenta (the temporary organ by means of which the fetus receives nourishment and discharges waste) by way of fetal circulation. Bacterial infection is most often associated with premature rupture of the membranes and infection of the amniotic fluid.

Maternal rubella (German measles) occurring during the first eight weeks of pregnancy is associated with congenital (congenital disorder) malformation of the fetus in more than 50 percent of cases, the figure decreasing to about 20 percent by the 16th week and dropping sharply thereafter. Infection of the fetus with a virus of the cytomegalovirus type involves many organs, has a high fatality rate, and may result in severe brain damage in fetuses who survive. Infection by the intracellular parasite Toxoplasma gondii produces a disease called toxoplasmosis, which may cause death or may result in microcephalus (abnormal smallness of the head), hydrocephalus (excessive accumulation of fluid in the brain cavities), or mental retardation. Congenital syphilis may have a variety of effects in the infant, including involvement of the skin, liver, spleen, lymph nodes, and kidneys. Malformations of the bones and teeth appear later, and severe involvement of the central nervous system may become apparent after many years.

Just as infectious agents may cross the placenta, so also most drugs (drug) administered to the mother may pass through the placenta and have important effects on the fetus. A most dramatic and devastating example of this effect occurred in Europe during the early 1960s, when the birth of thousands of infants with absent or short limbs resulted from the maternal ingestion of the apparently harmless drug thalidomide. Anesthetics, analgesics (pain relievers), sedatives, antihypertensive drugs, and antibiotics all may have adverse effects on the fetus. Congenital goitres (enlargement of the thyroid) have been produced by administration of antithyroid drugs to the mother. It is now clear that adverse effects on the fetus must be considered whenever drug therapy of the mother is contemplated.

The abuse of narcotics or alcohol by the mother can also lead to dire fetal consequences. Infants born to mothers addicted to heroin, morphine, or other opiates commonly share their mothers' addiction and suffer withdrawal symptoms within 72 hours of birth. Many infants of alcoholic mothers are afflicted with a combination of malformations, known as the fetal alcohol syndrome, which include mental retardation, growth retardation, and microcephaly.

The entire nutrient supply of the fetus derives from the mother. Although maternal deficiency states may, therefore, be reflected by parallel deficiencies in the fetus, in general the needs of the fetus will be met ahead of those of the mother, and an adequate amount of a given nutrient may be supplied to the fetus, despite maternal deficiency. Mild to moderate deficiencies of iron or calcium in the mother, for example, are not usually associated with deficiencies in the fetus. On the other hand, protein and caloric malnutrition may be associated with decreased fetal size.

Deficiencies in the fetus may also arise from placental (placenta) dysfunction (malfunctioning). The consequences of abnormalities of the placenta depend upon the time of onset and the severity of placental inadequacy. Serious placental insufficiency early in pregnancy may result in the death of the fetus. It is also likely that placental insufficiency can be a factor in decreasing fetal growth. Toward the end of pregnancy, placental dysfunction is associated with premature delivery or evidence of varying degrees of fetal distress, ranging from yellow staining of the skin to fetal wasting and to signs of severe lack of oxygen.

The physical trauma of delivery may result in a number of injuries to the infant. Of little consequence is the diffuse soft-tissue swelling of the scalp referred to as caput succedaneum. Difficult delivery may result in more extensive bruising, abrasions, and edema—particularly after breech delivery; however, serious harm is rare. Bleeding under the periosteum (parturition) (the covering membrane) of the skull produces a large swelling in 1 to 2 percent of babies, and in some it is associated with a small fracture of the underlying skull; fortunately, spontaneous healing occurs speedily. Injuries to the spinal cord are rare, but injuries of peripheral nerves as a result of traction on the head are not uncommon. Such injuries include Erb's paralysis, with weakness of the arm and shoulder because of damage to the fifth and sixth cervical nerves. Injury to the phrenic nerve, with paralysis of the diaphragm—the muscular partition between the chest and the abdomen—and facial-nerve injury resulting in facial palsy also are encountered. In the vast majority of such instances of peripheral-nerve injury, recovery is complete.

An extremely important form of birth injury is that associated with lack of oxygen (anoxia). Fetal anoxia may occur from inadequate oxygenation of the mother, low maternal blood pressure, or abnormalities in the uterus, placenta, or umbilical cord that result in inadequate blood flow to the fetus. After birth, anoxia may result from blood loss, shock, or inadequate respiration. Clinical manifestations include decreased activity, slowing of the heart, and blueness of the skin (cyanosis). Severe anoxia may cause death of the newborn, although recovery is more common. The major significance of anoxia is that it may result in brain damage if prolonged more than a few minutes.

The usual length of the gestation period is 40 weeks. Infants born prior to 37 weeks of gestation are considered to have been born early and are referred to as preterm or premature. Infants who at birth weigh 2,500 grams (about 5.5 pounds) or less are considered to be of low birth weight and either are prematurely born or have had less than the expected rate of growth within the uterus.

Infants whose weight is low at birth account for as many as 10 to 15 percent of births among low socioeconomic groups and as few as 4 to 5 percent of births among those of higher socioeconomic status. Clinical examination of the baby helps to differentiate between the preterm baby and the small baby born at term, but such determination of gestational age (the age from conception to birth) is not precise. The correct classification of the baby is important because maturity, in terms of gestational age, is a major factor determining the ease with which the baby will adapt to life outside the uterus. In the infant born too early, many organ systems will not be fully developed. The preterm infant who is large and only slightly immature does as well as the full-term infant, but the very small preterm infant, below 1,000 grams (about 35 ounces) in weight, has a high fatality rate and is prone to many complications.

The complications encountered in coping with extrauterine existence involve primarily the respiratory and gastrointestinal systems. In addition to anatomical immaturity of the lungs, a handicapping feature of the premature infant may be a lack of a substance called a surfactant (surface-active agent), which plays an important role in permitting the air spaces, or alveoli, of the lungs to remain open. Surfactant appears in some fetuses at 24 weeks' gestation but is absent in others until about 30 weeks. Because of these respiratory handicaps—particularly the lack of surfactant—many premature infants suffer from respiratory distress syndrome, a condition described below under Respiratory disorders (childhood disease and disorder).

Inability to suck adequately and limitations in the capacity to digest foodstuffs and absorb them through the intestinal tract provide other serious handicaps for the premature infant. To circumvent these problems, infants may be fed (by stomach tube) specially prepared formulas tolerated by even the smallest of babies.

The relatively large surface area of the small infant and his inability to maintain body temperature may require his being kept in an incubator. In addition to temperature control, the incubator makes it possible to provide extra oxygen to the infant who has respiratory difficulties, although this must be done with care because excessive oxygen may lead to damage to the eyes, a condition known as retrolental fibroplasia.

As indicated above, the prematurely born infant is considerably less likely to survive than are full-term infants. Premature infants, accounting for less than 8 percent of all live births, account for two-thirds of infant deaths. Even after the first year of life, the mortality rate among infants with low birth weights is greater than among infants with birth weights above 2,500 grams. The cause of this increased rate is not completely known, although a higher prevalence of congenital anomalies accounts for some of the difference. Moreover, retarded intellectual development and other abnormalities of the nervous system are more common in such infants, particularly those with birth weights of less than 1,500 grams (3.3 pounds). The majority of infants with low birth weights remain small throughout the childhood years, which may reflect a continued pattern of slow growth, first evidenced in the uterus.

Infants of diabetic (diabetes mellitus) mothers represent a unique group with special metabolic problems. Intrauterine death is common and unexplained. The placenta is often abnormal. The infants at birth generally are large and have large organs, a condition referred to as macrosomia. Respiratory distress and low levels of sugar in the blood (hypoglycemia) are common complications.

Neonatal hypoglycemia is a relatively common disorder, particularly among infants whose birth weight is low. Fifteen percent of hypoglycemic infants have associated abnormalities of the central nervous system. In most instances hypoglycemia is transient and responds readily to treatment.

Jaundice in the newborn is ordinarily related to an imbalance between the rate of destruction of red blood cells and the metabolism of hemoglobin to bilirubin and the rate of excretion of bilirubin in the bile; there is a resultant temporary elevation of bilirubin level in the blood. Jaundice may, however, be due to septicemia, to several different diseases of the liver, or to obstruction of the ducts through which bile flows into the intestinal tract. Abnormally high bilirubin levels have also been found in association with breast feeding; it is an extremely rare condition resulting from the presence of an unusual substance in the milk.

The significance of jaundice depends on the underlying cause and the amount of excess bilirubin in the blood. In extreme cases, bilirubin can be deposited in brain cells, resulting, as mentioned above, in severe nerve-cell damage, called kernicterus. This condition, which may lead to deafness and cerebral palsy, is encountered most often in infants with erythroblastosis fetalis, a blood disorder discussed below. Brain damage from an excess amount of bilirubin can usually be prevented by means of exchange transfusions (in which most of the infant's blood is replaced with blood from donors), which in the most severe cases may need to be repeated many times.

In contrast to the metabolic disturbances described above, which are generally transient conditions of the newborn, are the long-term disorders known as the inborn errors of metabolism. These result from the absence of a functional enzyme in a particular metabolic pathway. Because of this “enzyme block,” there is a deficiency in the products of the affected pathway and an excessive build-up of harmful chemicals that cannot be processed normally. Inborn errors of metabolism are genetically determined, and most are very rare. Many lead to severe illness and brain damage unless effective and early treatment can be started. A well-known example is phenylketonuria, which can be detected by a simple blood-screening test (the Guthrie test) during the first week of life. Once identified, the affected infant is given a special diet that prevents brain damage and allows normal growth. The diet has to be continued until at least the age of 10 years, and some clinicians recommend that it be followed for life.

The newborn infant is subject to the ordinary infections and, in addition, to infection with commonly encountered organisms such as Escherichia coli, Staphylococcus aureus, and group B hemolytic streptococci, which are not usual causes of serious infection in older age groups. Infection may be acquired in the uterus, during delivery, or later, in the nursery. Commonly encountered serious infections are pneumonia, meningitis (inflammation of the coverings of the brain and spinal cord), and septicemia (infection of the bloodstream). Often the infant shows few signs of the disease other than poor feeding, lethargy, pallor, or slight fever. Since the newborn infant's resistance to infection is poor, early diagnosis and treatment are particularly important. Often, treatment is given when infection is merely suspected.

Congenital defects of each part of the immunologic system have been discovered. The most striking feature of these diseases is the inability of the patient to combat infection. Thus, untreated patients with some forms of agammaglobulinemia (lack of antibodies in the blood) may die from overwhelming infection in infancy or early childhood.

Numerous abnormalities of respiratory function are common in the newborn infant. One of the most severe is respiratory distress syndrome (respiratory distress syndrome of newborns) (RDS; also called hyaline membrane disease). RDS occurs in 0.5 to 1 percent of all deliveries, and, as previously mentioned, is especially common in premature infants. In addition, it is encountered commonly in infants of diabetic mothers and after cesarean section (delivery through the wall of the mother's abdomen). RDS also occurs, albeit infrequently, in full-term infants without any apparent predisposing cause. Soon after birth, affected infants begin to take rapid, shallow breaths and can be shown by appropriate tests to be exchanging air (i.e., absorbing oxygen and exhausting carbon dioxide) only poorly. Without expert treatment, they may die within a few hours or may have a protracted course over a period of several days, with later demise or gradual improvement and recovery. Treatment is directed at relieving the symptoms and includes correction of an associated acidosis, administration of oxygen, and assisting the infant to breathe, if necessary with a mechanical ventilation machine. With modern care, death has become less common.

An infant may inhale meconium (a semisolid discharge from the infant's bowels) during the course of delivery, leading to obstruction of the upper airway. Clearing the airway with suction, the administration of oxygen, and general respiratory support are usually effective in promoting recovery within two to three days.

Leakage of air into the pleural space (between the membrane lining the chest and that enveloping the lungs and other thoracic organs), with consequent partial or complete collapse of the lung (pneumothorax), bleeding into the lung, and failure of expansion of the lung (atelectasis), also causes respiratory failure in the newborn infant. Prompt treatment is often necessary to ensure survival.

Cardiovascular disturbances in the newborn are related primarily to congenital malformations that affect about seven out of every 1,000 infants. They vary from those that are incompatible with life to those that cause no illness and require no treatment. Sometimes the cause is known because of an association with a chromosomal disorder (e.g., Down's syndrome and Turner's syndrome; see below); in a few the cause is maternal rubella infection. The lesions arise early in fetal development, and the result is usually either an obstruction of normal blood flow or an abnormal communication between different parts of the heart (congenital heart disease) or the circulation. When the structural abnormality causes severe disturbance, heart failure results. The baby in heart failure may present such symptoms as a blue complexion (cyanosis), breathlessness, or feeding difficulties. Most congenital heart defects are associated with heart murmurs that can be heard with a stethoscope. The most common congenital lesion is a ventricular septal defect, which is a hole between the two lower chambers of the heart (the left and right ventricles). Many of these close spontaneously without treatment. Diagnosis of an infant with suspected congenital heart disease has been made surer and easier with the development of echocardiography. Most of the disorders that cause illness can be corrected by surgery, which—unless the defect is immediately life-threatening—is usually deferred until the child is older. For a fuller discussion of specific congenital cardiovascular defects, see cardiovascular disease: Congenital heart disease (cardiovascular disease).

A specific cardiovascular problem common in the preterm infant is patent ductus arteriosus, which is the persistence of an essential feature of fetal circulation. The ductus arteriosus is a fetal blood vessel that connects the descending aorta and the pulmonary artery. It shunts blood from the lungs (which are nonfunctional in the fetus), channeling it toward the placenta (where oxygenation takes place). Normally, the ductus closes shortly after birth. When it remains patent (open) after birth, it functions as a shunt in the opposite direction, diverting blood from the aorta to the lungs. Thus, too much blood is delivered to the lungs, and the subsequent pulmonary congestion causes breathing difficulties. Drugs can be given to encourage the ductus to close. If drug treatment proves ineffective, the ductus may be closed surgically.

The diseases affecting the blood of newborn infants include diseases of the red blood cells (particularly the anemias, which involve an inadequate level of functioning hemoglobin in the blood) and of the clotting factors (e.g., hemophilia). These diseases and others that affect the blood of the newborn are discussed below, in the sections dealing with disorders associated with later infancy and childhood, and are covered in blood disease.

Erythroblastosis fetalis is a disease in which the red blood cells of the fetus are destroyed because of an incompatibility between the infant's blood and that of the mother. The severest form results from incompatibility between an Rh-negative mother and an Rh-positive fetus. If the mother has been sensitized (by previous exposure) to Rh-positive red blood cells, she will have circulating antibodies against the Rh factor. These antibodies can cross the placenta and destroy the red blood cells of her Rh-positive fetus. Unless the mother has been sensitized by blood transfusions, her first Rh-positive fetus is normally not affected. This is because her exposure to the fetal red blood cells is minimal until the delivery of the baby, when there is substantial transfer of fetal red blood cells to the maternal circulation. This exposure can sensitize the mother, and any future Rh-positive fetuses will be at risk. It is now standard procedure to administer anti-Rh serum promptly to an Rh-negative mother who has given birth to an Rh-positive child. The serum destroys any fetal red blood cells in her circulation before she becomes sensitized, thereby protecting future Rh-positive fetuses from erythroblastosis fetalis.

Vomiting, a common symptom among newborn infants, may be due to intestinal obstruction or to overfeeding or may occur without apparent cause. Continuous contraction of the muscle governing the opening between the stomach and the intestine may cause vomiting. This condition, called pyloric stenosis, may occur at any time in early infancy and usually requires surgical treatment.

The first bowel action and passage of meconium by the baby usually occurs within 12 hours. Delay may indicate an obstruction of the bowel. Important causes of obstruction are congenital narrowing (stenosis) or occlusion (atresia) of the intestine. These can occur at any site—from the duodenum (the first section of the small intestine) to the rectum and anus. Some babies are born with a small dimple or pit rather than a patent anus. Duodenal stenosis is particularly common in babies with Down's syndrome. Congenital obstructions of the intestines cause vomiting and constipation in early life; most can be corrected surgically.

Meconium ileus, intestinal obstruction by hard lumps of meconium, occurs almost exclusively in infants with cystic fibrosis, an inherited disease that is described below. Recovery, except in some instances of perforation of the intestine, is the rule.

The kidneys of the newborn infant are entirely capable of maintaining homeostasis, or balance, of fluids and electrolytes in normal circumstances, adapting readily, for example, to the various formulas utilized in infant feeding, despite the wide range of solute content and the consequent large variation in the excretory load imposed. (Electrolytes, in this context, are substances that become ionized in solution; that is, are given a positive or negative electrical charge.) In situations of stress, however, abnormalities in the regulation of salt and water balance and of acid–base metabolism are common. Limitations in the excretory capacity of the newborn infant's kidneys require adjustment of drug dosage and fluid therapy.

The most common disorders of the kidneys and urinary tract encountered in the neonatal period are congenital anomalies. Some, such as absence of one kidney, do not matter, since one healthy kidney will suffice; but other infants are born with no kidneys or with malformed (dysplastic) kidneys that function poorly. Polycystic disease of the kidneys is an example of a serious congenital abnormality. In this disorder, the kidneys contain numerous large cysts that severely impair renal function.

Congenital obstructions of the urinary tract—either of the ureter above the bladder or of the urethra below it—predispose the infant to urinary infection and to kidney damage. Failure of a newborn to pass urine within 12 hours of birth leads to a search for possible obstruction.

Nephritis (Bright disease) (inflammation of the kidneys) is rare in the newborn. In one well-known type—congenital nephrosis—large amounts of protein are lost in the urine, with consequent development of severe, generalized edema. The outlook for recovery in congenital nephrosis and in other forms of nephritis in infants is extremely poor.

Infections of the kidneys and urinary tracts are difficult to recognize clinically in young infants. If, however, they are diagnosed early and treated promptly, such infections respond well to treatment, unless there is an associated congenital obstructive lesion.

Congenital malformations of the nervous system rank among the most common severe congenital abnormalities. A variety of brain malformations may occur, some incompatible with life (e.g., anencephaly—the absence of the cerebral hemispheres), others resulting in permanent disability. Common brain malformations include microcephaly, an abnormally small head due to limited brain growth, and hydrocephalus, in which there is an increase in the volume of cerebrospinal fluid associated with increased pressure. The obvious evidence of the latter condition is the large size of the head. Some infants with hydrocephalus die before birth. After birth, the condition may arrest spontaneously. The major treatment is relief of pressure by diversion of the spinal fluid or by surgical correction of any obstruction. The prevention of progressive damage is the goal of therapy.

Acquired conditions, including those secondary to insufficient oxygen and bleeding, have been mentioned above in the section on birth injuries. meningitis (inflammation of the coverings of the brain and spinal cord) may occur in the newborn. Unfortunately, the diagnosis is often delayed because of the lack of characteristic symptoms and findings in infants.

Convulsions (seizures) are common in the newborn. These may result from damage to the brain during delivery or from infections and metabolic problems.

Although rare, congenital defects of the endocrine (hormone-producing) glands can have severe consequences. Congenital hypothyroidism (subnormal secretion by the thyroid glands (thyroid gland), also called cretinism) is an especially important endocrine disease of infancy in that failure to identify and treat it early may result in severe mental retardation. It is due either to an absence of the thyroid or to a metabolic disturbance in the function of the gland. Early diagnosis and proper therapy with thyroid drugs result in dramatic improvement, with rapid disappearance of all signs and symptoms of disease. In countries with well-developed health services, a drop of the newborn's blood is used in a chemical screening test for cretinism. Effective treatment thus can be initiated shortly after birth.

Congenital adrenal hyperplasia is a group of conditions in which there is a defect in the production of normal adrenocortical-steroid hormones (secretions of the cortex, or outer substance, of the adrenal glands). Excessive stimulation of the cortex of the adrenals by a pituitary hormone (adrenocorticotropic hormone, or ACTH) results in abnormal enlargement of the glands and overproduction of androgenic (masculinizing) adrenal hormones. As a result, there may be abnormal development of the genitalia of females in utero and evidence of excessive androgenic effect in either sex during infancy, with accelerated growth, premature appearance of pubic hair, and enlargement of the phallus.

Common congenital musculoskeletal defects include abnormalities of the feet and the hips. Classic clubfoot, or talipes equinovarus, is a congenital twisting of the foot in which the heel bends upward and the front part of the foot is turned inward and bent toward the heel. Correction usually involves the use of splints and plaster casts to force the foot into the correct position; severe cases may necessitate surgery. In talipes calcaneovalgus, the front part of the foot is bent upward and turned outward. This form of clubfoot generally results from mechanical pressure in the uterus having held the foot in an unusual posture. Passive stretching exercises usually can correct this condition, but stubborn cases may require the use of splints or casts.

Congenitally dislocated (dislocation) hips are associated with lax joints and are most common in girls born at term by breech delivery. The condition is usually detectable by careful clinical examination and, if diagnosed early, responds to simple treatment. If undetected until a two-year-old is noticed to walk with a limp, major surgery may be needed.

The infant's skin has a thin epidermis and immature glands and is particularly susceptible to blistering and infection. Diaper, or napkin, rashes, which affect the areas of skin in contact with a wet diaper, are very common and can become severe when additional infection occurs.

There are many common birthmarks. Most result from either developmental anomalies of the blood vessels, called hemangiomas, or from an excess of pigment in the skin, called nevi. A common worry to parents is the “strawberry” hemangioma, which is red, raised, and unsightly. Although it may increase in size in the early weeks, it gradually fades away by the age of seven years. A Mongolian blue spot, usually on the buttocks or back, looks like a faint bruise and is a common pigmented birthmark in infants of black or Oriental stock. It fades and is rarely visible after the age of seven.

A normal person has 46 chromosomes, but sometimes developmental faults occur that result in the fetus' having extra chromosomes. Most of these abnormal fetuses result in miscarriages or stillbirth, but those with Down's syndrome (Down syndrome) (mongolism) commonly do survive. Down's syndrome occurs approximately once in every 600 births. The affected child carries an extra chromosome number 21 and has a characteristic appearance that includes a round skull; flat face; oblique eyes; small, drooping mouth; and a short, broad neck and hands. The main problem of Down's syndrome victims is moderate to severe mental retardation. As adults, most are incapable of leading independent lives. They also suffer from an excess of respiratory infections in early life and have an increased incidence of serious congenital abnormalities. In developed countries, however, most of them grow up to be reasonably healthy adults, though their life expectancy is shorter than that of a normal person.

Disorders of the sex chromosomes (sex chromosome) are also common. These disturb the development of the gonads more than they influence the external genitalia; therefore, many of the conditions are not diagnosed until after puberty, when the child (or parents) becomes concerned about the lack of development of sexual characteristics. Normal girls have two X sex chromosomes. Those with Turner's syndrome have a single X chromosome. The syndrome may be detected early in life because the girls are short and have other visible characteristic features. The diagnosis can only be confirmed, however, by careful analysis of the chromosomes in the blood cells. These girls remain short, and secondary sexual characteristics do not appear unless additional hormones are given. Even then, an affected girl remains infertile because her uterus, vagina, and gonads are very small.

Normal boys have one X chromosome and one Y sex chromosome. Those with Klinefelter's syndrome have an extra X chromosome. Although the condition occurs as often as Down's syndrome, it is not usually detected until the testicles fail to enlarge at puberty. The boys are healthy, but infertility is usual.

It is well documented that more males than females are affected by nonspecific mental handicaps (mental disorder) and that in some families the males are regularly affected. Several different forms of mental handicap linked with the X chromosome in the male have been identified. In some of the affected males, a “fragile site” can be identified on the X chromosome with appropriate laboratory techniques. Such males are said to have the fragile-X syndrome.

In developed countries, SIDS (also called crib death or cot death) accounts for 20 percent of deaths between the ages of one month and one year. SIDS is a categorization rather than an explanation, for the label is given when no reason for death can be found from the infant's medical history or even after autopsy.

Most crib deaths occur in the first five months of life and strike at home during the night. They are more common in the winter and in poor social circumstances. A preceding minor respiratory infection is common. This has prompted some investigators to suggest that the underlying defect is the presence of a virus in the bloodstream, leading to instability of cardiac and respiratory mechanisms. Many other hypotheses have been proposed to explain such deaths, however, and it is likely that several different causes may be involved.

Failure to thrive is the term used to describe the condition in which a young child fails to gain weight satisfactorily. Common reasons for such poor weight gain are parental neglect or lack of food. On the other hand, a large number of important gastrointestinal disorders may be responsible, including those associated with vomiting, such as food intolerance or obstruction of the upper bowel by pyloric stenosis; disorders of digestion and absorption, including celiac disease and cystic fibrosis; and bowel infections. Alternatively, the body, because of other serious disorders (e.g., chronic infection or heart or kidney disorder), may fail to use the food that is given and absorbed appropriately.

Malnutrition refers to any disorder brought on by improper diet. In developed countries, the most common form of malnutrition is obesity, the excess accumulation of fat brought on by a diet containing too many calories. obesity is a major contributor to ill health throughout life. In nonindustrialized nations, by contrast, most malnutrition stems from the lack of food or of particular nutrients. Such deficiency diseases remain an enormous problem. In addition, specific nutritional disturbances are encountered regularly in all populations.

Malnutrition due to inadequate intake of food results in muscle wasting, stunted growth, pallor, increased susceptibility to infection, and fatigue. A special form of malnutrition, in which the intake of calories is adequate but that of protein is not, is referred to as kwashiorkor; it is prevalent in areas of Africa, Asia, and Latin America. Kwashiorkor primarily affects children from six months to five years of age, the onset usually coinciding with the child's being weaned from breast milk (which provides adequate protein) to a diet consisting largely of starchy carbohydrates. The affected children are small, have excess fluid in their tissues, and often have enlarged livers. They have unusual pigmentation of the skin and sparse, reddish hair. Permanent aftereffects of kwashiorkor, especially on the intellectual functions, are matters of great concern.

Vitamin deficiencies can result in a variety of diseases. rickets is a disorder secondary to deficiency of vitamin D. The major consequence is bone disease, with defective growth of the epiphyseal cartilage. (This cartilage, present in several bones, especially near the ends of the long bones of the arms and legs, ossifies as a person matures.) scurvy occurs as a consequence of a deficiency of vitamin C. Clinical manifestations include bone disease, irritability, and bleeding under the skin and mucous membranes. pellagra is due to a deficiency of niacin and is manifested clinically by diarrhea, dermatitis, and dementia. Riboflavin deficiency results in lesions of the skin and corners of the mouth, with a peculiar smoothing of the tongue. beriberi is a consequence of thiamine (thiamin) deficiency. The major clinical features often relate to cardiac impairment. Defects in the functioning of the nervous system also are common. Deficiency of vitamin A results in ocular abnormalities, growth retardation, anemia, and dermatitis.

All of the various types of infectious disease, which can involve virtually every organ and every part of the body, are encountered in children. There are, however, certain infectious illnesses that have become almost synonymous with the term childhood disease. These diseases occur chiefly among children, and one bout usually provides lifelong immunity against further attacks. Such classic infectious diseases of childhood include the exanthematous viral infections (i.e., measles, chicken pox, German measles, and other viral infections that produce skin eruptions) and mumps. The incidence of these diseases, which were once endemic among childhood populations throughout much of the world, now varies markedly. Smallpox, the most serious of the exanthematous viral diseases, has been eradicated worldwide through immunization programs. Other classic childhood disorders—including measles, German measles, and mumps—have been all but eradicated via immunization in countries with high standards of medical care. They remain endemic, however, in areas with poorer health-care systems.

German measles, or rubella, is a milder disease, also viral, with an incubation period of 14 to 21 days. As discussed earlier, its major significance is the likelihood of its causing severe malformations of the fetus if contracted by the mother during the first three months of pregnancy.

Chicken pox (chickenpox) (varicella) is a highly contagious viral disease with an incubation period of 13 to 17 days. At the start there is mild to moderate fever, followed by a generalized eruption of papules, small, solid elevations that appear in crops, initially small and red, becoming vesicular (i.e., becoming small blisters). After several days, no new lesions develop, and the vesicles gradually crust over and heal. Severe itching usually accompanies the rash.

The common cold, or acute nasopharyngitis, the most common respiratory disease in children, is caused by a large number of viruses and may be complicated by superimposed bacterial infection. There is no specific treatment.

Enlargement of the adenoids (lymphoid tissue in the nasal part of the pharynx) as a result of recurrent infection can result in mouth breathing and a so-called adenoidal facial appearance, the most conspicuous feature of which is the constantly open mouth. By blocking the eustachian tube, it can contribute to infections of the middle ear (otitis media) and to hearing loss. In children with chronic middle-ear disease and a specific type of hearing loss, removal of adenoids may be indicated.

Allergic rhinitis (inflammation of the nasal passages) is the most common allergic disorder of childhood. Seasonal allergic rhinitis, or hay fever, due to sensitization to house dust, pollen, or molds, is characterized by attacks of sneezing, nasal itching, and a watery nasal discharge during the season when the specific allergens are prevalent. Similar symptoms are present in perennial allergic rhinitis but without seasonal pattern. In addition to inhalants, sensitization to specific foods may underlie the disorder. Treatment consists of avoidance of the substances causing the reaction, desensitization, and use of decongestant drugs and antihistamines (drugs that, by inactivating the histamine given off by injured cells, suppress many of the symptoms of an allergic attack).

In discussing childhood respiratory diseases, tuberculosis and cystic fibrosis should be included. Both of these disorders predominantly affect the lungs, although many other organs may also be involved. Tuberculosis continues to be a major world health problem. As countries improve public-health standards and increase their socioeconomic level, the illness and mortality from this disease decrease steadily. Tuberculosis appears mostly in a primary form consisting of a small localized lesion of the lung that either heals completely or remains quiescent for many years. Only infrequently among children does the disease extend to involve other parts of the lung or other parts of the body, such as bones, kidneys, or the central nervous system. Miliary tuberculosis, a generalized form of infection, and tuberculous meningitis are the most severe forms of the disease and have an extremely high mortality, although recovery may occur with proper treatment. These forms most commonly occur in young children. As with other diseases, tuberculosis is better prevented than treated. A form of immunization (BCG—bacille Calmette–Guérin—vaccine) is utilized in areas of the world in which the disease is endemic. In other areas, control depends on prevention of contacts and early identification and treatment, if necessary, of infected individuals. A variety of antibiotic agents is effective in treatment, particularly the drugs isoniazid and rifampin.

Sinusitis, otitis, bronchitis (inflammation of the sinuses, the ears, and the bronchi, respectively), and pneumonia occur commonly in children and do not differ in essential detail from the same diseases in adults. Other conditions that affect children and adults alike are described in respiratory disease .

Congenital heart defects, treated earlier in this article, rank among the most common sources of cardiovascular difficulties in children. Among acquired heart diseases in children, rheumatic fever is the most important cause worldwide, although it has become far less common and less severe in developed countries. Rheumatic fever strikes mainly between the ages of five and 15, occurring as an abnormal reaction to a beta-hemolytic streptococcal throat infection of a few weeks previous. Heart involvement may not be apparent early, but 60 percent of the victims develop rheumatic heart disease in later life; mitral stenosis (narrowing of the mitral valve) is a particularly common complication.

Most disorders of cardiac rate (cardiovascular disease) and rhythm in childhood are benign. An exception is paroxysmal atrial tachycardia, a disorder characterized by a steady, rapid heart rate, which in infants may exceed 300 beats per minute. If the disorder persists, it may lead to heart failure. Treatment with digitalis usually restores normal rhythm.

Bacterial endocarditis (bacterial infection of the heart lining) occurs most frequently in children with preexisting heart disease. The most common organism is the alpha streptococcus, which accounts for 80 percent of cases. Common symptoms are fever, a sense of ill health, and fatigue. The outlook depends on the sensitivity of the infecting organism to antibiotic drugs, the age of the affected child, and the type of underlying heart disease.

Virtually all of the recognized blood diseases (blood disease) of adults are encountered in children. Of particular importance are the conditions in which abnormal types of hemoglobin are formed. The abnormal hemoglobin present in sickle-cell (sickle cell anemia) anemia, also called sickle-cell disease and sicklemia, must be inherited from both parents to cause the disease, the effects of which include hemolytic anemia (anemia involving destruction of red blood cells and release of their hemoglobin) and recurrent crises with episodes of painful swelling of the hands and feet, abdominal pain, and increase of the anemia. Persons who have inherited the defect from one parent and are said to have the sickle-cell trait constitute approximately 10 percent of the U.S. black population. There are a number of other abnormal hemoglobins. thalassemia, or Cooley's anemia, is a condition in which there is severe, progressive hemolytic anemia, beginning at about six months of age. Like sickle-cell anemia, thalassemia is a recessive hereditary disorder and thus must be inherited from both parents. It occurs in a broad equatorial belt extending from the Mediterranean countries through India to the Far East. Its underlying defect is the deficient production of adult hemoglobin (hemoglobin A). Repeated transfusion of blood and, in certain instances, removal of the spleen are the only available treatments.

The most common form of anemia in infants and children is caused by iron deficiency. Fetal stores of iron usually prevent development of anemia during the first six months of life, but it is common thereafter, when the diet may not be adequate to meet the high requirements for iron. Apart from pallor, children usually are well, although they may show irritability and lack of appetite. Treatment consists of the administration of iron and modification of the diet to include sufficient iron to prevent recurrence.

Congenital disorders of the coagulation process usually become manifest during infancy or early childhood. The most common of these is hemophilia, a disease caused by deficiency in a specific coagulation factor. The disease is manifested only in males who have inherited the trait from their mother and occurs in about one of every 10,000 male births. Treatment consists of intravenous injection of the deficient factor, along with measures to control bleeding locally and transfusion of blood when necessary.

Abdominal pain, one of the most common symptoms of childhood, can be indicative of many gastrointestinal disorders (digestive system disease) but usually occurs without evidence of disease. Recurrent abdominal pain without detectable disease may be a psychosomatic disorder. See also digestive system disease.

Acute appendicitis occurs in all age groups, although it is rare in extremely young infants. The clinical manifestations (abdominal pain, vomiting, fever) in older children are similar to those in adults. In infants and younger children, the systemic manifestations are more severe, and rupture of the appendix is more frequent.

Young children often put things in their mouths, and sometimes they accidentally swallow them. Foreign bodies lodged in the esophagus must be removed. Objects small enough to pass through the esophagus into the stomach usually will pass through the entire intestinal tract, and no treatment is necessary.

Food intolerance is an important cause of vomiting, diarrhea, and failure to thrive in early life. Sometimes the intolerance to a specific food item is temporary, so all that is required is avoidance of that substance for a few months. Other intolerances are more serious and may require lifelong avoidance. celiac disease is caused by a peculiar sensitivity to the gluten fraction of wheat, rye, or other cereals; therefore, symptoms develop after the introduction of cereals into the diet. Affected children characteristically pass large, bulky, greasy stools; have poor appetite; and are generally miserable. Although they are thin, there may be marked gaseous abdominal distension. The diagnosis is usually made by a biopsy of the affected segment of the intestine (the jejunum). Treatment, consisting of exclusion of gluten from the diet, has a dramatic effect within a few weeks. The patient needs to remain on the special diet throughout childhood and probably should continue it throughout life.

Intolerance to particular sugars may be associated with gluten sensitivity or may occur on its own. The disaccharide sugars—for example, sucrose (table sugar) or lactose (milk sugar)—are the most common offenders. Inability of the intestine to handle these sugars in the normal way leads to diarrhea, malabsorption, and failure to thrive. Fortunately, sugar intolerance is generally a transient event.

Viral hepatitis (inflammation of the liver due to infection with a virus) has its highest incidence but lowest mortality rates among children of school age. Two main forms of the disease, hepatitis A and hepatitis B, occur in children. These two forms were distinguished initially by their clinical characteristics and are now recognized to be caused by two different viruses. Hepatitis A (infectious hepatitis) is highly contagious and can be passed from person to person directly, as well as being acquired from contaminated water or food. It is particularly common in communities with poor sanitation. Hepatitis A has an incubation period of 14 to 40 days and usually has an abrupt onset. Fever, headache, and feelings of ill health are followed by loss of appetite, nausea, and vomiting. Jaundice ensues, and the liver becomes enlarged and tender. Improvement is usually noted in a few weeks. In children, complete recovery is common.

Hepatitis B (serum hepatitis) is acquired as a result of receiving blood or blood products from someone who is a carrier of the disease. Thus, it may be acquired from a blood transfusion or from being inoculated with a contaminated needle used by another person (e.g., among drug addicts using the same needle). It has a much longer incubation period (60 to 160 days) and more gradual onset than does hepatitis A. The clinical symptoms are much the same as in hepatitis A, and the outlook for recovery is good in children.

Infection of the urinary tract is common and occurs predominantly in females. The most frequent infection is cystitis, a superficial infection of the lining of the bladder, but pyelonephritis, infection of the kidney, is not uncommon. Escherichia coli is the organism responsible in 80 percent of the cases. Symptoms of cystitis include urgency, frequency, painful urination, and suprapubic pain (pain just above the frontal pelvic bones). Pyelonephritis may be without symptoms or may cause fever, back pain, and shaking chills. The patient, who should drink plenty of fluids and void frequently, usually receives antibiotics, which clear the infection rapidly. Ultrasound or X-ray investigation for underlying congenital abnormalities is especially important in young children. Infection recurs in up to 50 percent of cases.

The presence of bacteria in the urine without manifestation of symptoms (asymptomatic bacteriuria) is found in about 1 percent of schoolgirls. This condition is associated with an increased frequency of minor voiding disturbances, of urinary-tract abnormalities, and of symptomatic urinary infections in later life.

Various forms of glomerulonephritis (Bright disease) (kidney disease in which there is inflammation of the glomeruli—the knots of minute blood vessels in the capsules of the nephrons, the functioning units of the kidneys) affect children. The type most commonly encountered in children worldwide—though infrequently seen in developed countries—is acute post-streptococcal nephritis. This disorder occurs as a late complication of infection with certain strains of group A beta streptococci. The onset is heralded with blood in the urine, excess fluid in the tissues, or headache due to high blood pressure. Spontaneous recovery ordinarily occurs. A rare patient with unusually severe disease may suffer irreversible kidney damage.

The nephrotic syndrome is a group of symptoms that occurs as a consequence of any kidney disease; characteristically, there is excretion of great amounts of protein in the urine, and generalized edema occurs in the absence of evidence of glomerulonephritis or systemic disease. Most of these children respond to treatment with adrenocortical steroids and ultimately recover. As previously mentioned, congenital nephrosis is an especially severe form that may be apparent at the time of birth. There is no effective treatment, and infants do not usually survive beyond the first year of life.

All forms of glomerulonephritis described in adults are seen also in children. If sufficient information is available, most instances of hereditary nephritis can be shown to have their onset in childhood.

Disorders of specific tubular functions (i.e., functioning of the nephrons) are rare. Nephrogenic diabetes insipidus is a disease of male infants in which there is failure of the kidneys to respond to antidiuretic hormone, with consequent inability to concentrate urine. The symptoms are polyuria (copious urine), polydipsia (excessive thirst), and chronic dehydration. The Fanconi syndrome is a group of diseases in which there are multiple abnormalities in renal-tubular function. In one of these, cystinosis, there is progressive impairment in renal function.

Children with renal failure (kidney) and uremia (nitrogenous wastes in the blood) can be treated with dialysis and renal transplant. The major role of dialysis in children is to support patients until a transplant can be performed. Transplant of a kidney from a living, related donor yields the best results, but many children have had successful transplants of kidneys from cadavers (see transplant).

Congenital anomalies of the nervous system are common and have been discussed earlier in this article.

Mental retardation (intellectual disability) is a major problem, affecting about 0.5 percent of young children. For the majority the cause is unknown. Fortunately, most retarded children have only a mild handicap, with an intelligence quotient (IQ) between 50 and 75, and are, therefore, educable and trainable to a reasonable degree of independence as adults. Up to 15 percent of affected children have a more severe handicap, however, and cannot be expected to be independent as adults.

Brain tumours (tumour) are the second most common malignancy of childhood (after leukemia); they are, nevertheless, very rare. The most common brain tumours are situated at the base of the brain and are associated with raised intracranial pressure, causing head enlargement or pain and vomiting. Scanning by computerized axial tomography, which provides a cross-section image of the brain, helps with the diagnosis. A combination of radiotherapy and surgery may be successful in treating such tumours.

Convulsive disorders (convulsion) in children are common. As many as 5 percent of children have a seizure at least once during their lifetime. So-called febrile seizures occur in association with high fever. They are most common between six months and four years of age, and there is a high familial incidence. Spontaneous recovery is usual. Epilepsy, or recurrent seizures, has a prevalence of about 0.5 percent. There are many known causes, but in most cases none is found. Treatment with anticonvulsant drugs is successful in suppressing seizures in most cases.

Eighty percent of all cases of meningitis occur in the first five years of life, and the majority of these strike during the first two years. In most cases, meningitis results from a bacterial or viral infection of the cerebrospinal fluid. Bacterial meningitis is a serious acute illness, in that the bacterial infection may damage the brain permanently. By contrast, most of the common viral causes—including the mumps virus—rarely produce serious illness. Poliomyelitis, however, is a serious form of viral meningitis because of the risk of permanent paralysis. Fortunately, poliomyelitis is rarely seen in countries that provide mass immunization against the disease. The diagnosis of meningitis is made by analyzing a sample of cerebrospinal fluid withdrawn by needle from the spinal canal (i.e., by lumbar puncture). Effective antibiotic therapy is available for the bacterial forms.

In addition to the congenital disorders discussed earlier, a variety of endocrine diseases can occur during childhood. These include precocious puberty, hyperthyroidism, pituitary or adrenal insufficiency, and diabetes mellitus.

Precocious puberty includes a large group of conditions in which there is premature onset of sexual development. Although precocious puberty can result from disease of the brain, adrenals, or gonads, in most instances no underlying disease can be detected.

Overactivity of thyroid function, or hyperthyroidism, is uncommon. Affected children exhibit nervousness, weight loss, irritability, and hyperactivity. Usually there is enlargement of the thyroid gland. A variety of drugs that suppress thyroid function is available. In some instances, surgical removal of most of the thyroid gland is indicated.

General pituitary (pituitary gland) or adrenal insufficiency results in deficiencies of many hormones and produces a complex disturbance of many body functions, usually requiring urgent treatment. Therapy consists of administration of those hormones that are not being produced in sufficient quantity. A deficiency of the pituitary secretion growth hormone may exist without other deficiencies, in which case it causes merely extreme shortness, the child being otherwise well. Once the condition has been identified by serial measurements of the rate of growth and by measurement of growth hormone in the blood, injections of growth hormone can restore the child to normal height.

Skin disorders are common during childhood. Birthmarks and diaper rashes (both considered above), eczema, and local infections are often seen.

Eczema (dermatitis) is characterized by reddening of the skin, papules, oozing, and crusting with intense itching. In infants the lesions often appear first on the cheeks and then develop on other areas, while older children are most affected on the insides of the elbows and the knees. Treatment includes attention to any underlying allergic causes and local application of a variety of different medications, especially adrenocortical-steroid ointments.

Impetigo contagiosa (impetigo) is a superficial infection of the skin with Staphylococcus aureus or hemolytic streptococci. Vesicular or pustular lesions exude moisture and become crusted. Untreated, the lesions tend to become widespread and may involve any area of the skin or the scalp. Treatment consists of keeping the affected areas clean and local or systemic administration of antibiotics.

Fungal infections of the skin are also common. thrush, a disease characterized by small, white spots in the mouth or a diffuse rash on the body, affects infants infected by the fungus Candida albicans. In the older child, tinea capitis (ringworm of the scalp), tinea corporis (ringworm of the body), and tinea pedis (athlete's foot) are all common superficial fungal infections.

Warts (wart), also called verrucae, are the most common viral skin infection and are probably more common in childhood than at any other time. The average life of a wart is three to four months, so treatment is usually reserved for long-lasting warts. On the sole of the foot a verruca that becomes rather flattened is called a plantar wart.

Various parasites may cause skin infestations. The common head louse (Pediculus humanus capitis) causes irritation of the scalp and lays tiny, whitish eggs (nits) on the hair. Head lice are easily eradicated by the application of special lotions to the scalp of the child (and the rest of the family). scabies is an infection caused by the itch mite (Sarcoptes scabici), which lays its eggs in burrows beneath the skin. After a few weeks of infestation, the child becomes sensitized to the parasite and develops an itchy rash, particularly on the hands and armpits. The infestation is transferred by bodily contact, so that other family members are commonly infected, and all should be treated with creams or lotions that eradicate the mite.

Henoch-Schönlein purpura (anaphylactoid purpura) is the most common connective-tissue disorder in children. It is characterized by a purpuric rash, painful swollen joints, and abdominal pain with vomiting. In a minority of patients, the kidneys become involved and nephritis develops; this is the only complication that may cause permanent damage. In general there is complete recovery.

Juvenile rheumatoid arthritis, or Still's disease, is rare. In very young children it is characterized by general illness, fever, and rashes, with comparatively mild joint involvement. In older children, the adult pattern of the illness is seen, with predominant joint involvement and little or no general illness. More than half of affected children make a complete recovery; the rest have recurrences requiring treatment.

In developed countries, accidents cause more loss of life and disability among children (except infants) than any disease. Road-traffic mishaps account for nearly half of the accidental deaths—usually the child involved being a pedestrian or cyclist. Accidents in the home, by way of burns and falls, account for another quarter. Boys are more at risk than girls, particularly if they are from a large family living in a poor, inner-city area. Children are more likely to suffer serious burns and scalds than adults because of the fact that their skin is thin and more liable to full-thickness damage.

Accidental poisoning (poison) is very common, particularly among two- to four-year-olds, who are inquisitive and use their mouths to feel and taste new objects. Accidental ingestion of household fluids and medicines is common. Fortunately, it is usual for the child to swallow only a tiny amount, and severe illness from such poisoning is rare. Medicinal drugs are much more likely to cause illness than are household and garden products, berries, or toadstools.

Lead poisoning has become less common worldwide, though there is increasing worry about prolonged exposure to low levels of lead and its possible relationship to abnormal childhood behaviour and intelligence. Low-level lead poisoning generally results from unavoidable exposure to atmospheric lead pollutants. This is a problem in some heavily industrialized areas and in those regions where leaded gasoline is still burned in automobiles.

The spectrum of child abuse is wide. It includes not only children who have suffered physical abuse with fractures and bruises (“the battered child”) but also those who have experienced emotional abuse, sexual abuse, deliberate poisoning, and the infliction of fictitious illness on them by their parents (Munchausen syndrome by proxy). Children under the age of two are most liable to suffer direct physical abuse at the hands of their parents. Such abuse is more common in families who are poor and are living under stress and in which the parents themselves suffered cruelty as children. Frequently, the child shows other evidence of poor nutrition or neglect. Most developed countries have a well-established system for dealing with suspected cases of abuse, involving child-protection agencies, social workers, and, if necessary, the police.

Sexual abuse, in which dependent, developmentally immature children are involved in sexual activities that they do not fully comprehend and to which they cannot give informed consent, has become increasingly recognized. Girls are involved mainly, and their fathers are the usual offenders. Sexual abuse frequently does not come to light until the older girl develops a psychosomatic illness, runs away from home, or is truant from school.

All disorders have both a physical and psychological component. For many disorders—such as asthma, eczema, and ulcerative colitis—the importance of physical and emotional factors varies at different times during the course of the disease. Moreover, the individual's concept of illness and his worries about it inevitably contribute to the severity and duration of a particular illness. A three-year-old may have no concept of disease or of time. Consequently, he may not worry about the cause or duration of a disease but instead be much more upset by immediate discomforts associated with the illness. A young child may view admission to the hospital as particularly frightening and unpleasant. Unless the parents can be with him, he may see their absence as a complete loss and cannot appreciate that he may be back with them and well two days later. Thus, great efforts are made to avoid hospitalizing children. When a youngster is admitted to a hospital, the parents are encouraged to be with him as much as possible and, when conditions permit, to sleep beside the young child in the hospital.

In other ways, the fact that the young child has no concept of illness is an advantage, for as soon as an acute illness is over, the child resumes normal health with startling rapidity—he does not feel in need of convalescence in the way that an adult does after a frightening experience. Children have great and speedy powers of recovery.

Minor behaviour disturbance involving enuresis (urinating), soiling (defecating), or sleep disorders are common. Most children who exhibit such behaviours should not be considered psychologically abnormal. Similarly, habit spasms (tics) involving repetitive involuntary movements, usually of the head and neck, are extremely common, affecting up to 10 percent of 10-year-olds.

Severe behaviour disorders are much less common, and true childhood psychosis is most uncommon. Hyperactivity (attention-deficit/hyperactivity disorder) is a behaviour disorder characterized by perpetual overactivity. Hyperactive children refuse to concentrate on one task for long, are always on the go, and need relatively little sleep. They are very easily distracted, and, because of the lack of concentration, school problems arise. The incidence of hyperactivity varies enormously from country to country, and it is likely that local fashions and beliefs greatly affect the criteria for diagnosis. Most young children are very active and exhaust their parents, and few concentrate on their schoolwork as much as their parents wish. Thus, parents often see a child as overactive and readily suggest hyperactivity as the problem, though strict measurement of psychological criteria rarely demonstrates its presence. Enthusiasts embark on behaviour-modification therapy and sometimes drug therapy.

During adolescence, body weight almost doubles, and an additional 25 percent in height is gained. Secondary sexual characteristics appear, menstruation begins in girls, spermatogenesis (sperm formation) starts in boys, and fertility is established in both sexes. Adolescents establish a sense of identity and achieve a degree of independence that ultimately prepares them to take their place in adult society. It is expectable, therefore, that the major disorders of adolescence concern problems of growth, sexual development, and psychological disturbances.

Disturbances of growth (child development) chiefly concern short stature in boys and tall stature in girls, both conditions being a potential source of psychological handicap. Although organic and genetic causes of short stature in boys must all be considered, most relatively short but otherwise healthy children are simply late maturers. Graphic plots of height gain with age reveal steady, normal progression but a delayed pubertal growth spurt, concordant with the delay in sexual maturation. With further sexual maturation, acceleration in growth will occur, and adult height within normal limits will be achieved. Similarly, many excessively tall adolescent girls are early maturers; with early sexual and skeletal maturation, their linear growth stops at an adult height well within normal limits.

The sequence of sexual development (sexual behaviour, human) in girls is extremely variable. Widening of the bony pelvis, growth of the nipples and breasts, changes in external and internal genitalia, and the menarche occur sequentially as pituitary gonadotropin (sex-gland-stimulating hormone) causes ovarian release of estrogen (female sex hormone). Axillary (armpit) and pubic hair and some of the changes of the external genitalia develop under the stimulus of androgens of adrenal origin. Since these arise from a different source of pituitary stimulation, there is considerable variation among girls in the relationship of their appearance and, for example, development of the breasts. Recognition of this helps to allay anxieties over “abnormal” sexual development.

Sexual development in boys usually follows a more predictable sequence, although there is great variation in the time of onset of puberty and the time of achievement of full sexual maturation. Stimulation of the testes by pituitary gonadotropins results in the release of the hormone testosterone, which causes growth of the internal and external genitalia, development of pubic, axillary, and facial hair, changes in the larynx that result in deepening of the voice, and increased statural growth and muscular development. In about half of all boys, noticeable swelling of mammary-gland tissue occurs midway through adolescence. When the enlargement of the breasts is great enough to engender concern, it is called gynecomastia. In most instances, the enlargement disappears spontaneously.

Acne vulgaris (common acne) is a prevalent skin condition that has its onset during adolescence. At puberty, androgenic stimulation of the skin's sebaceous (oil) glands (which empty into the canals of the hair follicles) causes increased production of the fatty substance sebum. In susceptible individuals, there is oversecretion of sebum. Sebum and cellular debris then form a plug in the follicle canal, and the growth of bacteria in the plug produces unsightly pustules. Prolonged treatment is often needed.

The psychological (psychological development) disturbances of adolescence are universal and protean, ranging from minor emotional upsets to schizophrenia—from mild feelings of inadequacy to suicide. The sexual and aggressive impulses of the preadolescent period are complicated by the advent of physical and sexual maturity. Both an inability to control urges and desires and an excessive degree of self-control are characteristic. Some adolescents remain too dependent on their parents; others attempt to achieve independence too quickly. As many as 10 percent of adolescents may have psychological disturbances that seriously interfere with their functioning and the development of social relations.

One well-known major psychological disorder that generally begins in adolescence is anorexia nervosa. The onset is usually at puberty. The victims, overwhelmingly girls, at first appear healthy but then refuse to eat, and they lose weight. As they lose weight they begin to look ill, and expert help is required in order to encourage them to eat again and regain health. Anorexia nervosa is rare.

Unfortunately, certain other major behavioral disturbances of adolescence have become increasingly prevalent in the late 20th century. suicide has become much more common; suicidal gestures are particularly common in girls. In many industrialized countries, suicide ranks as the second or third most common cause of death during adolescence (after accidents and, in some countries, malignancy). Delinquency, vandalism, and dropping out of school have become increasingly widespread and are often associated with addiction to drugs or alcohol.