A disorder, often of genetic origin, although sometimes related to a severe neurological illness in early infancy. There is a wide spectrum of how it presents from some children who do not develop speech at the expected time and who are profoundly learning disabled and with major behavioural abnormalities (Kanne's Syndrome) to those who are of normal (or above normal) intelligence whose main difficulty is with forming conventional social relationships (ASPERGER'S SYNDROME).