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Twin Autism Project

researchersThe Twin Autism Project is a relatively new project and is currently in its first funding cycle; therefore, published data on the full sample of twins is not yet available. However, preliminary results from the project were presented at the Behavior Genetics Association's 35th Annual meeting in June 2005.

Twin Concordance for the Autism Spectrum Based on Community Diagnoses and Screening of a Birth Cohort

Inferences about the degree of genetic influence on individual differences in the autism spectrum depend crucially on the relative risk to siblings and the differential concordance of monozygotic (MZ) versus dizygotic (DZ) cotwins. Previous European twin studies that used older diagnostic criteria for autism revealed concordance rates suggesting strong genetic influence; however, concordance rates for the spectrum using current diagnostic criteria are still unknown. A decrease of relative risk rates for siblings over time suggests that the autism spectrum, as currently diagnosed, is heritable, but not as strongly heritable as classic autism was. Our sample comprised 2808 individual twins screened at 2 years of age (mean 27 mos.) after being recruited from 1998 to 2003 state birth records. Our 35 screening items were drawn from an autism screener combined with items from the Infant Toddler Social Emotional Assessment. The screener items were divided into four subscales measuring speech, social behavior, restricted interests, and motor impairment. We focused on twins who had extreme scores (top 5%) on both the social and speech subscales (social-speech score). A probandwise analysis of the top 5% of social-speech scores revealed an MZ concordance rate in the .60s and a DZ rate in the .40s. An independent case-finding approach has identified 95 twin pairs in the state of Wisconsin in which at least one twin has an autism spectrum diagnosis. Of these 95 twin pairs, we identified 13 individual twins with a later autism spectrum diagnosis who had previously been administered the screener. Eight of the 13 scored in the top 4% of social-speech scores and four others placed in the top 12%. The pairwise concordance rates for 79 of the 95 twin pairs (zygosity of twins or diagnosis of cotwin were unknown for 16 pairs) were 77% for MZ and 28% for DZ pairs. Although more thorough analysis and in-depth study of both twins with extreme screener scores and the twin pairs found through case-finding is still underway, the preliminary evidence suggests that the autism spectrum is heritable, although not as strongly heritable as the earlier European twin studies of autism indicated.

Kees, E.K., Hefter, R.L., Klaver, J., Schweigert, S.A., Arneson, C., Gernsbacher, M.A., & Goldsmith, H.H. (2005, June). Twin concordance for the autism spectrum based on community diagnoses and screening of a birth cohort. Behavior Genetics, 35, 809. (abstract).


University of Wisconsin-Madison :: Department of Psychology :: Waisman Center
University of Wisconsin, Madison
Psychology Department, University of WI, Madison
Waisman Center, UW Madison