Subgrouping siblings of people with autism: identifying the broader autism phenotype

We investigate the spectrum nature of autism and the extent to which a "broader phenotype" can be observed in siblings of individuals with autism spectrum conditions (ASC). The Autism-Spectrum Quotient (AQ) was used to measure autistic traits in typical control participants, siblings, and volunteers with ASC. Using cluster analysis, we derived a model with two sibling subgroups: low-scorers and high-scorers. We found that, while siblings as a single 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.