Fragile X Syndrome, Autism and Autistic Features

Abstract

The relationship between fragile X syndrome and autism is reviewed. Results from a semi-structured questionnaire survey of development and behaviour in boys with fragile X syndrome, Down's syndrome and learning disability of unknown aetiology are presented. A behavioural profile characteristic of many boys with fragile X syndrome was identified which distinguished them from both other groups. Fragile X boys did not show more autism than boys with idiopathic learning disability but they did have a common autistic-like profile of communicatory and stereotypic disturbances, most notably delayed echolalia, repetitive speech and hand flapping. Boys with idiopathic learning disability showed difficulties more in areas of social functioning. Boys with Down's syndrome were characterized by fewer difficulties in social functioning and ritualistic/stereotypic tendencies but this might have been explained by subject ascertainment bias. Behavioural items distinguishing boys with fragile X significantly from both other groups retained their significance even when individuals with autism were excluded from statistical analysis. The findings provide further support for the notion of a behavioural phenotype in boys with fragile X syndrome.