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Study reanalysis suggests autism strongly linked with genetics

Reanalysis of a previous study indicated heritability of autism spectrum disorder was 83%, suggesting that risk for autism may be largely explained by genetic factors.

“Studies have found that autism spectrum disorder (ASD) aggregates in families and twin studies estimate the proportion of the phenotype variance due to genetic factors (heritability) to be about 90%,” Sven Sandin, PhD, of Ichan School of Medicine at Mount Sinai, New York, and colleagues wrote. “In a previous study, ASD heritability was estimated to be 0.5, and shared familial environmental influences to be 0.04. 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.”

To determine heritability of ASD, researchers used an alternate method to define concordant and discordant sibling pairs within the same data as the previous study, a population-based cohort of children born in Sweden from 1982 through 2006. Follow-up for ASD was conducted through 2009. The study cohort included 37,570 twin pairs; 2,642,064 full sibling pairs; and 432,281 maternal and 445,531 paternal half-sibling pairs.

Overall, 14,516 children were diagnosed with ASD.

Researchers chose a model including additive and nonadditive genetic, shared and nonshared environmental parameters as the full model in which submodels were tested.

Estimated ASD heritability was 0.83 (95% CI, 0.79-0.87) and nonshared environmental influence was 0.17 (95% CI, 0.13-0.21).

The full model estimated shared environment variance as 0.04 (95% CI, 0-0.14); nonshared environment variance as 0.16 (95% CI, 0.05-0.3); non-shared additive genetic variance as 0.1 (95% CI, 0-0.38); and additive genetic variance as 0.69 (95% CI, 0.4-0.86).

Analysis of only twins indicated heritability was estimated as 0.87 (95% CI, 0.68-0.96).

“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 one affected child, and, coupled with the time trends in ASD prevalence, the heritability estimates are sensitive to the choice of methods,” the researchers wrote. “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.” – by Amanda Oldt

Disclosures: Sandin reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.