Identical twins with autism spectrum disorder (ASD) who are raised together can show significant differences in symptom severity, according to research in Behavior Genetics. Researchers analyzed data from three studies with a total of 366 identical twin pairs (ages 4 to 15) with and without ASD. The children’s behavioral traits related to autism (e.g., social interaction and repetitive behavior) were assessed by standard instruments involving parents’ or clinicians’ observations. The researchers reported a 96% likelihood that if one twin had ASD, the other had it, too. However, trait scores varied much more between twins diagnosed with ASD than between twins without ASD. The researchers suggest that ASD may be associated with greater vulnerability to influences from the environment that are not shared between siblings. Finally, these data qualify understanding of the foundational statistic of monozygotic twin concordance in autism. Our findings confirm probandwise categorical concordance statistics consistent with marked heritability for ASD.

https://www.apa.org/monitor/2020/04/inbrief

https://link.springer.com/article/10.1007/s10519-019-09987-2