In order to establish a diagnosis of Asperger’s syndrome (ASP) [3-6], the DSM-IV requires, as for ASD, the fulfillment of at least two symptoms of impaired social interaction and at least one symptom of restricted, repetitive behavior. However, the ASP diagnosis, in contrast to the ASD diagnosis, does not require a symptom of impairment in communication, nor must any of the symptoms show an onset before age 3 years. According to the DSM-IV, ‘Asperger’s Disorder can be distinguished from Autistic Disorder by the lack of delay in language development. Asperger’s Disorder is not diagnosed if criteria are met for Autistic Disorder’ [2]. Data for the prevalence of ASP are not reliably available, owing to the use of slightly differing diagnostic criteria in the literature. For example, Mattila et al. [7] applied four different criteria on the same group of 5,484, eight-year-old children and found prevalence rates varying from 1.6 to 2.9 per 1,000. Kopra et al. [8] similarly compared various diagnostic criteria and concluded that ‘the poor agreement between these sets of diagnostic criteria compromises comparability of studies (of Asperger’s syndrome)’.
