Sex Differences in the Broad Autism Phenotype: Insights from the Australian Biobank.

Examining sub-threshold autistic traits in non-autistic first-degree relatives of individuals on the autism spectrum, known as the Broad Autism Phenotype (BAP), could provide new insights into the associations and familial aggregation of autistic traits. This study was a retrospective cross-sectional study of parents (n = 1008), probands with autism (n = 613), and unaffected siblings (n = 221) of probands with autism. BAP traits were examined by the BAP Questionnaire and Communication Checklist-Adult in parents, Autism Developmental Observation Scale-Second edition in probands, and Social Responsiveness Scale in siblings. Multivariable linear regression analyses were used to investigate the associations of parental BAP traits on autistic traits in probands and unaffected sibling BAP traits. Fathers showed significantly increased aloofness, pragmatic language difficulties, and social engagement problems compared to mothers. Female siblings showed increased difficulties with social cognition compared to male siblings. Adjusted models of the regression analyses showed that all BAP traits in fathers were significantly associated with BAP trait expression in probands with autism. Additionally, all of mother's BAP traits were significantly associated with unaffected siblings' BAP trait expression while only fathers' aloofness and rigidity traits were inversely associated with siblings' BAP trait expression. Finally, there were significant inverse interactions noted between parent's BAP traits and their children's BAP trait expression. This study demonstrated differences in how males and females express BAP traits and also identified differences in parent-child associations by sex, with fathers having a greater effect on their proband children's expression of BAP traits than mothers.