an inability or pronounced difficulty to learn to read or spell, despite otherwise normal intellectual functions. Dyslexia is a chronic neurological disorder that inhibits a person's ability to recognize and process graphic symbols, particularly those pertaining to language. Primary symptoms include extremely poor reading skills owing to no apparent cause, a tendency to read and write words and letters in reversed sequences, similar reversals of words and letters in the person's speech, and illegible handwriting.

Dyslexia is three times more common in boys than in girls and usually becomes evident in the early school years. The disorder tends to run in families. Only a minority of dyslexics remain nonreaders into adulthood, but many dyslexics continue to read and spell poorly throughout their lifetime. Dyslexics frequently perform above average on nonverbal tests of intelligence, however. Dyslexia is best treated by a sustained course of proper instruction in reading. The cause of the disorder is unknown; dyslexia is usually diagnosed for children or adults who have reading difficulties for which there is no apparent explanation.