human disorder with many characteristics of premature aging (human aging). Affected persons have parchment-like skin, become bald or gray-haired early in life, and tend to develop diseases related to aging decades before they occur in normal individuals. Initially, progeria was studied as a model of normal aging, but because not all organs are affected, this is no longer thought to be appropriate. There is, for example, no evidence of senility or of aging in the central nervous system. Two major types of progeria occur: the extremely rare Hutchinson–Gilford syndrome, which has its onset in early childhood, and Werner's syndrome, which is unrelated and occurs later in life. A third disease, progeria with microphthalmia (the Hallerman–Streiff–François syndrome), in which dwarfism is a prominent feature, is also sometimes included.

Signs of infant progeria, the Hutchinson–Gilford syndrome, appear at about age one, after an evidently normal infancy. Affected individuals seldom exceed the size of a normal 5-year-old, although they have the physical appearance of 60-year-old adults by the time they are 10. Many of the superficial aspects of aging, such as baldness, thinning of the skin, prominence of blood vessels of the scalp, and vascular diseases, occur. Sex organs remain small and underdeveloped. A few individuals with progeria are mentally retarded, but most have normal intelligence and may even be precocious. By age 10, extensive arteriosclerosis and heart disease have developed, and most patients die before they reach 30; the median age of death is 13. A hereditary basis has been suspected, but there is no evidence to support the suspicion, and the cause remains a mystery.

Werner's syndrome, sometimes called progeria of the adult, appears in young adulthood or, less commonly, in late adolescence. The aging changes are somewhat less pronounced, so that affected persons look about 30 years older than their chronological age. There is no dwarfism, as growth has been completed by the time the disease appears, but affected persons tend to be slightly shorter than average. Patients with Werner's syndrome are sexually mature, but secondary sex characteristics are poorly developed. Superficial signs of aging are premature balding or graying of hair, loss of teeth and hearing, cataracts, acute arthritic episodes, skin ulcers, and osteoporosis (loss of bony tissue). There is an increased tendency to develop heart disease, diabetes mellitus, and cancer, and the average lifespan is 47 years. This type of progeria is hereditary and is transmitted as a recessive trait, but its underlying cause is unknown.