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Autism Heritability Estimate Updated in New Analysis of 2014 Swedish Study

NEW YORK (GenomeWeb) – Taking a second look at data from a large Swedish study of families with autism spectrum disorder (ASD) diagnoses, researchers have re-estimated the heritability of the syndrome, upping it to 83 percent.

Numerous studies have concluded that ASD aggregates in families, evidence that it has at least some hereditary component. One such analysis published in JAMA in 2014, a study of tens of thousands of siblings and half-siblings born in Sweden between 1982 and 2006, initially estimated the heritability of ASD — or the risk of developing the disorder if your family member has been diagnosed with it — to be 50 percent.

In a letter in JAMA today, a group led by Sven Sandin of the Icahn School of Medicine at Mount Sinai reported that they reanalyzed the data from that study using a new method that they believe offers a more accurate result. The authors wrote that their new analysis not suggests genetic factors explain a significant amount for ASD, but that these genetic factors explain much more of the risk than they initially reported.

According to the authors, the rarity of ASD means that 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," they wrote, whereas the team's new estimate this week "more accurately captures the role of the genetic factors."

In the initial study, researchers from Icahn and the Karolinska Institute in Sweden used a data set that took into account something called "time-to-event effects," which they wrote this week may have reduced their heritability estimates. To reassess their results, the team went back to the raw study data — incidence numbers for autism amongst the thousands of families that were followed — and tested various models that either included or excluded certain genetic and environmental parameters to find the one that best fit the data.

Using the best-fitting model, which only included additive genetic and nonshared environmental parameters, the team estimated ASD heritability at 83 percent. This suggests that environmental influence only contributes 17 percent to the risk of developing the disorder.

The researchers wrote that their estimate of 83 percent is "slightly lower than the approximately 90 percent estimate reported in [some] earlier twin studies and higher than the 38 percent estimate reported in [one California twin study."

Though the investigators wrote that they believe their updated risk estimate is more accurate due to the superior methodology, they added that it is important to note that both their current and previous analyses found that heritability of ASD was high and the risk of developing the disorder increased with increasing genetic relatedness.