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Since the seminal twin study of autism in 1977 that found that autism co-occurred in 36% of monozygotic twins and 0% in dizygotic twins (J Child Psychol Psychiatry 1977; 18:297), research has focused on causative genetic versus environmental factors to explain these high familial rates. Now, researchers have conducted a reanalysis of a 2014 study to correct a methodological problem.
In the original analysis, an unaffected twin of an autistic sibling was censored at study entry. In the new version, both affected and unaffected siblings were followed. Participants, born from 1982 to 2006, included approximately 38,000 twin pairs, 2.6 million sibling pairs, and 878,000 half-sibling pairs; participants were followed until 2009. Heritability was …