[Fragile X chromosome in autism and psychotic disorders in children].

Three cases of fragile X (fra X) have been identified in a systematic survey of 30 boys, aged 3 to 14, with infantile autism or psychotic disorders, associated with mental retardation. Only one of these children exhibited a dysmorphy characterizing the Martin-Bell syndrome. Two fra X cases fulfilled the DSM III criteria for autism; none corresponded to the Kanner's description of infantile autism. The prevalence of fra X among children with psychotic disorders (6%) is much higher than in the general population; however it is close to the prevalence observed in non psychotic mentally retarded patients. Given the inconsistency of the somatic phenotype, the screening should benefit from the recent discovery of abnormal methylation of DNA.