No evidence for or against an increase in prevalence

Autism seems to be on the increase. This at least is the feeling of many professionals in the field of child development in Britain, who believe that in recent years they have been seeing more children with autistic spectrum disorders. Autism was first characterised in 1943 by Kanner,1 who described a group of children with an unusual pattern of behaviour present from birth or before 30 months. He called this “early infantile autism.” His essential criteria for diagnosis were social aloofness and elaborate repetitive routines.2 Subsequent epidemiological studies have shown that autism is not, as Kanner first thought, a unique and separate condition occurring in children of otherwise normal development but that it is closely related to a range of developmental disorders.3 4 These include Asperger's syndrome,5 a condition characterised by borderline or normal IQ; social isolation or naive, inappropriate social interaction; intensive interest in only one or two subjects; a narrow, repetitive life style; limited or inappropriate intonation and body language; and poor motor coordination.

Autistic spectrum disorders share a triad of impaired social interaction, communication, and imagination, associated with a rigid, repetitive pattern of behaviour. Onset is usually at birth or during the first three years of life, but problems can begin later in childhood. The triad can be recognised at all levels of intelligence and can …