- Compared identical (MZ) twins to fraternal (DZ) twins.
- Compared the concordance of actual autism diagnoses using an established diagnostic test.
- Had some way of determining which twins were identical or fraternal without having to resort to estimates.
There are plenty of studies that compare "autistic traits" in twins (I found at least 11 of these) but surprising few that look like they would meet the criteria above. So far I have found these -
- Folstein, S, and M Rutter. 1977. “Infantile autism: a genetic study of 21 twin pairs.” Journal of child psychology and psychiatry, and allied disciplines 18:297-321. http://www.ncbi.nlm.nih.gov/pubmed/562353
- Ritvo, ER, B J Freeman, A Mason-Brothers, A Mo, and AM Ritvo. 1985. “Concordance for the syndrome of autism in 40 pairs of afflicted twins.” The American journal of psychiatry 142:74-7. http://www.ncbi.nlm.nih.gov/pubmed/4038442
- Steffenburg, S et al. 1989. “A twin study of autism in Denmark, Finland, Iceland, Norway and Sweden.” Journal of child psychology and psychiatry, and allied disciplines 30:405-16. http://www.ncbi.nlm.nih.gov/pubmed/2745591
- Bailey, A et al. 1995. “Autism as a strongly genetic disorder: evidence from a British twin study.” Psychological medicine 25:63-77. http://www.ncbi.nlm.nih.gov/pubmed/7792363
- 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)
- Taniai, Hiroko, Takeshi Nishiyama, Taishi Miyachi, Masayuki Imaeda, and Satoshi Sumi. 2008. “Genetic influences on the broad spectrum of autism: study of proband-ascertained twins.” American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics 147B:844-9. http://www.ncbi.nlm.nih.gov/pubmed/18361421
- Schweigert,E. K., Gernsbacher,M. A., Hefter,R. L., Gottesman, I. I., Goldsmith, H. H. (2009, May). Twin Concordance for Autism: a Comparison of Multiple Diagnostic Criteria in a Population-Based Twin Study. INSAR Poster. http://imfar.confex.com/imfar/2009/webprogram/Paper4692.htm
- Rosenberg, Rebecca E et al. 2009. “Characteristics and concordance of autism spectrum disorders among 277 twin pairs.” Archives of pediatrics & adolescent medicine 163:907-14. http://www.ncbi.nlm.nih.gov/pubmed/19805709.
- Hallmayer, Joachim et al. 2011. “Genetic Heritability and Shared Environmental Factors Among Twin Pairs With Autism.” Archives of general psychiatry 1-8. http://www.ncbi.nlm.nih.gov/pubmed/21727249 (Accessed July 10, 2011).
Does anyone know of any others?