Author Affiliation: Offord Centre for Child Studies, McMaster University, Hamilton Health Sciences, Hamilton, Ontario, Canada.
The year 1977 marked an important milestone in the history of autism. In this year, the first twin study in autism was published by Folstein and Rutter1; it demonstrated a striking difference in concordance rates between monozygous (MZ) and dyzgyous (DZ) twins. The studies that followed reported even higher MZ concordance rates, up to 90%, for a broader phenotype resembling what is currently labeled as autism spectrum disorder (ASD)2- 4 and DZ concordance rates at or close to 0%. This resulted in heritability estimates greater than 90%, suggesting that almost all of the variance in phenotypic expression could be attributed to inherited genetic factors.
Szatmari P. Is Autism, at Least in Part, a Disorder of Fetal Programming?. Arch Gen Psychiatry. 2011;68(11):1091-1092. doi:10.1001/archgenpsychiatry.2011.99