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This study measures the distribution of autistic traits, using the autism-spectrum quotient (AQ), in siblings of individuals with autism spectrum conditions (ASC). Total AQ scores, along with AQ subscales, were collected from child, adolescent and adult controls, siblings, and volunteers with ASC using one of the three age-appropriate versions of the instrument: the AQ (adult self-report), the AQ-adolescent and AQ-child (both parent-reports). We examined the effect of Group (case, sibling and control) and AQ version (adult, adolescent and adult) on total and subscale scores. In addition, we tested for sex differences in all groups and on all versions. We found that in male and female adults, AQ scores in siblings fell between cases and controls (cases > siblings > controls). In children and adolescents, female siblings also scored higher than control females (female cases > female siblings > female controls), but there was no difference between male siblings and controls (male cases > male siblings = male controls). An investigation of subscale scores revealed that male siblings only differed from controls on the 'Communication' subscale (male cases > male siblings > male controls), while female siblings differed from controls on all subscales except 'Imagination' (female cases > female siblings > female controls). This study confirms the broader autism phenotype in siblings, and reveals this is modulated by sex and AQ version. Autism Res 2017, 10: 289-297. © 2016 The Authors Autism Research published by Wiley Periodicals, Inc. on behalf of International Society for Autism Research. [ABSTRACT FROM AUTHOR]

We investigate the broader autism phenotype (BAP) in siblings of individuals with autism spectrum conditions (ASC). Autistic traits were measured in typical controls ( n = 2,000), siblings ( n = 496), and volunteers with ASC ( n = 2,322) using the Autism-Spectrum Quotient (AQ), both self-report and parent-report versions. Using cluster analysis of AQ subscale scores, two sibling subgroups were identified for both males and females: a cluster of low-scorers and a cluster of high-scorers. Results show that while siblings as a group have intermediate levels of autistic traits compared to control individuals and participants with ASC, when examined on a cluster level, the low-scoring sibling group is more similar to typical controls while the high-scoring group is more similar to the ASC clinical group. Further investigation into the underlying genetic and epigenetic characteristics of these two subgroups will be informative in understanding autistic traits, both within the general population and in relation to those with a clinical diagnosis. Autism Res 2016, 9: 658-665. © 2015 The Authors Autism Research published by Wiley Periodicals, Inc. on behalf of International Society for Autism Research [ABSTRACT FROM AUTHOR]