by Bill Ahearn, PhD, BCBA-D, LABA Director of Research, NECC

Despite the ardent beliefs of many people that autism has a solely environmental cause such as vaccines, it has long been known that there is strong scientific evidence that autism has genetic origins. Early studies of twins suggested this may be the case and, more recently, Tick and colleagues (2016) conducted a meta-analysis of published research involving twins and estimated heritability (i.e., how well differences in people’s genes account for differences in their traits) of autism to be in the range of 64% to 91%.

Though there are some known environmental origins of autism, such as pregnant mothers contracting rubella having a much higher probability of their child receiving a diagnosis of autism, environmental variables may play a fairly small role in the population etiology of the disorder. However, environmental variables have received much more attention than genetic variables.

In July, Bai and colleagues (2019) published a study suggesting that the heritability of autism was approximately 80%, indicating that the variation in autism occurrence in the population is mostly due to inherited genetic influences, with no support for contribution from maternal effects (i.e., how much of the phenotype of a child is influenced by the environment experienced by the mother). The researchers examined the medical histories of more than 2 million (non-twin) children born in Denmark, Finland, Sweden, Israel, and Western Australia between 1998 and 2012. All were tracked for a diagnosis of autism from birth and were followed until age 16. Autism diagnoses were obtained through their medical record. Of those studied, over 22,000 had an autism diagnosis, for a prevalence in the group of 1.1%. The authors then used Generalized Linear Mixed Effect Models to estimate genetic and environmental effects on the risk for autism to obtain the heritability estimate.

In an editorial accompanying the article, Jutla et al. (2019) state that “the disorder is strongly heritable, with environmental factors, although important, contributing relatively less to its variance than genetic factors.” They then, by implication, suggest that this study may actually underestimate the contribution of genetic variables as it did not capture de novo (non-inherited) gene variations for which there are robust data suggesting such variations may contribute significantly to autism risk.

Bai, D., Yip, B.H.K., Windham, G.C., et al. (2019). Association of genetic and environmental factors with autism in a 5-country cohort. JAMA Psychiatry, 201976 (10), 1035–1043. https://doi:10.1001/jamapsychiatry.2019.1411.

Jutla, A., Reed, H., Veenstra- VanderWeele, J. (2019). The architecture of autism spectrum disorder risk: What do we know, and where do we go from here? JAMA Psychiatry, 201976 (10), 1005–1006. https://doi:10.1001/jamapsychiatry.2019.1375.

Tick, B., Bolton, P., Happé, F., Rutter, M., & Rijsdijk, F. (2016). Heritability of autism spectrum disorders: A meta -analysis of twin studies. The Journal of Child Psychology and Psychiatry, 57(5), 585-595. https://doi:10.1111/jcpp.12499.

This article was taken from NECC’s Research News, Winter 2019. You can find the full publication here.