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Am J Psychiatry. 2015 Mar 1;172(3):266-75. doi: 10.1176/appi.ajp.2014.14050576. Epub 2014 Nov 7.

Social responsiveness, an autism endophenotype: genomewide significant linkage to two regions on chromosome 8.

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From the Neurogenetics Program and Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles; the Center for Autism Research and Treatment, Semel Institute, David Geffen School of Medicine, University of California, Los Angeles; the Center for Neurobehavioral Genetics, Semel Institute, David Geffen School of Medicine, University of California, Los Angeles; the Interdepartmental Ph.D. Program in Neuroscience, Brain Research Institute, University of California, Los Angeles; the Departments of Psychiatry and Pediatrics, Washington University School of Medicine, St. Louis; and the Department of Human Genetics, University of California, Los Angeles.



Autism spectrum disorder is characterized by deficits in social function and the presence of repetitive and restrictive behaviors. Following a previous test of principle, the authors adopted a quantitative approach to discovering genes contributing to the broader autism phenotype by using social responsiveness as an endophenotype for autism spectrum disorder.


Linkage analyses using scores from the Social Responsiveness Scale were performed in 590 families from the Autism Genetic Resource Exchange, a largely multiplex autism spectrum disorder cohort. Regional and genomewide association analyses were performed to search for common variants contributing to social responsiveness.


Social Responsiveness Scale scores were unimodally distributed in male offspring from multiplex autism families, in contrast with a bimodal distribution observed in female offspring. In correlated analyses differing by Social Responsiveness Scale respondent, genomewide significant linkage for social responsiveness was identified at chr8p21.3 (multipoint LOD=4.11; teacher/parent scores) and chr8q24.22 (multipoint LOD=4.54; parent-only scores), respectively. Genomewide or linkage-directed association analyses did not detect common variants contributing to social responsiveness.


The sex-differential distributions of Social Responsiveness Scale scores in multiplex autism families likely reflect mechanisms contributing to the sex ratio for autism observed in the general population and form a quantitative signature of reduced penetrance of inherited liability to autism spectrum disorder among females. The identification of two strong loci for social responsiveness validates the endophenotype approach for the identification of genetic variants contributing to complex traits such as autism spectrum disorder. While causal mutations have yet to be identified, these findings are consistent with segregation of rare genetic variants influencing social responsiveness and underscore the increasingly recognized role of rare inherited variants in the genetic architecture of autism spectrum disorder.

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