The broader phenotype of autism : evidence from a genetically related sample

Background to study: Autism spectrum disorders (ASD) are the most common and heritable neuropsychiatric disorders of childhood, and arise due to multiple susceptibility genes. Previous studies have shown that the underlying genetic liability extends from individuals with ASD to relatives with milder, related disorders ' the Broader Autism Phenotype (BAP). Previously, groups searching for autism susceptibility genes have not utilised genetic data from siblings or parents of included probands. Identification and characterisation of the BAP in relatives is necessary before relative's genetic information can be used in the search for autism susceptibility genes. Methods: In order to characterise the BAP in relatives from families in which there were two or more individuals with an ASD, the Family History Interview (FHI) used in previous twin and family studies of autism was significantly reviewed. IMGSAC then collected BAP data on over 300 first degree relatives (age range 4-67 years) of ASD probands. Results: Analysis confirmed that the revised FHI identifies the phenotypic impairment associated with the BAP through previous research. Data gathered were both valid and reliable. Factor analysis of FHI data revealed that a strong clustering of social-communication impairments and rigidity underlie the BAP in both males and females. Conclusions: The FHI is a reliable interview which identifies social-communication impairments and rigidity as the core of the BAP. In the future, categorising relatives BAP status will allow the utilisation of their genetic information in both the search or autism susceptibility genes and in the eventual investigation of the phenotype-genotype relationship