Autism Spectrum Disorder Risk May Be Mostly Genetic

Heritability of autism spectrum disorder is estimated at 83 percent in a new study, suggesting that genetic factors may explain most of the risk.

Previous studies have found that autism spectrum disorder (ASD) aggregates in families. In one earlier study, ASD heritability was estimated to be 50 percent. To define presence or absence of ASD, the study used a data set created to take into account time-to-event effects in the data, which may have reduced the heritability estimates.

Using the same underlying data from this study, Sven Sandin, Ph.D., of the Icahn School of Medicine at Mount Sinai, New York, and colleagues used an alternate method (used by previous studies in the field) to calculate the heritability of ASD.

Autism Spectrum Disorder Heritability

The study included a group of children born in Sweden 1982 through 2006, with follow-up for ASD through December 2009. The analysis included 37,570 twin pairs, 2,642,064 full sibling pairs, and 432,281 maternal and 445,531 paternal half-sibling pairs.

Of these, 14,516 children were diagnosed with autism spectrum disorder. Various models were tested and using the best-fitting model, the ASD heritability was estimated as 83 percent and the non-shared environmental influence was estimated as 17 percent.

“This estimate [83 percent] is slightly lower than the approximately 90 percent estimate reported in earlier twin studies and higher than the 38 percent estimate reported in a California twin study, but was estimated with higher precision. Like earlier twin studies, shared environmental factors contributed minimally to the risk of ASD,”

the authors write.

Untestable Assumptions

The researchers note that twin and family methods for calculating heritability require several, often un-testable assumptions.

Because ASD is rare, estimates of heritability rely on few families with more than one affected child, and, coupled with the time trends in ASD prevalence, the heritability estimates are sensitive to the choice of methods.

“The method initially chosen in the previous study led to a lower estimate of heritability of ASD. The current estimate, using traditional methods for defining ASD discordance and concordance, more accurately captures the role of the genetic factors in ASD. However, in both analyses, the heritability of ASD was high and the risk of ASD increased with increasing genetic relatedness,”

the researchers write.

Sandin S, Lichtenstein P, Kuja-Halkola R, Hultman C, Larsson H, Reichenberg A
The Heritability of Autism Spectrum Disorder
JAMA. 2017;318(12):1182–1184. doi:10.1001/jama.2017.12141

Image: Alex Pang/Flickr