Genetic Factors Account for the Majority of Autism Risk

Megan Brooks

September 27, 2017

A reanalysis of data from a previous study on the familial risk for autism spectrum disorder (ASD) suggests that genetics contributes 83% of the risk for ASD.

The original study, which involved more than 2 million families, suggested that genetics contributes 50% of the risk for ASD. That study was published in JAMA in 2014 and was reported at that time by Medscape Medical News.

For the 2014 study, to define the presence or absence of an ASD, Sven Sandin, PhD, from the Department of Psychiatry, Ichan School of Medicine at Mount Sinai in New York City, and colleagues in Sweden used a data set created to take into account time-to-event effects in the data, which may have reduced the heritability estimates, they note.

For their reanalysis, using the underlying data from the original study, Dr Sandin and his coinvestigators utilized an alternate method to calculate the heritability of ASD, with far different results.

The results were published online as a research letter on September 26 in JAMA .

The analysis included children born in Sweden from 1982 through 2006; the patients received follow-up for ASD through December 2009. Participants included 37,570 twin pairs, about 2.6 million full-sibling pairs, 432,281 maternal half-sibling pairs, and 445,531 paternal half-sibling pairs. Of these, 14,516 children were diagnosed with ASD.

The researchers tested various models. Using the best-fitting model, the ASD heritability in the new analysis was estimated to be 0.83 (95% confidence interval [CI], 0.79 - 0.87). Using only twins, the heritability was estimated to be 0.87 (95% CI, 0.68 - 0.96).

The investigators note that the 83% estimate is "slightly lower" than the roughly 90% estimate reported in earlier twin studies and is higher than the 38% estimate reported in a California twin study, but that the estimate was made with "higher precision." Like earlier twin studies, shared environmental factors contributed minimally to the risk for ASD, they point out.

"Twin and family methods for calculating heritability require several, often untestable assumptions. Because ASD is rare, estimates of heritability rely on few families with more than 1 affected child, and, coupled with the time trends in ASD prevalence, the heritability estimates are sensitive to the choice of methods," Dr Sandin and colleagues write.

"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," they add.

The study was supported by the Beatrice and Samuel A. Seaver Foundation. One author has served as a speaker for Eli Lilly and Shire and has received research grants from Shire.

JAMA. Published online September 26, 2017. Abstract

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