Scientists have for decades relied on studies of twins to parse the genetic versus environmental contributions to complex syndromes. Assessing the degree to which a condition affects both members of a set of identical twins, who share the same genetic information, can yield an estimate of the extent to which genetics underlie that condition.
Two new papers explore the genetic and environmental underpinnings of autism using data from the Twins Early Development Study, which follows identical and fraternal twins born in England and Wales in the mid-1990s.
In the first study, published 27 December in the Journal of Child Psychology and Psychiatry, researchers looked at autism traits in 6,413 twin pairs from the Twins Early Development Study and examined autism heritability in a meta-analysis of seven published twin studies, representing another 8,508 twin pairs. Their study suggests that genes trump environment in a big way: When one identical twin has autism, there’s a 98 percent chance that the other twin also has the condition1.
The second study, published 26 November in the Journal of the American Academy of Child & Adolescent Psychiatry, involved 207 identical and fraternal twin pairs, 127 of which include at least one twin with autism2. The researchers found that some autism-linked behaviors are more genetic in origin than others. Specifically, genes appear to largely dictate disruptive behaviors, such as rule-breaking and violent outbursts, whereas environmental factors underlie emotional symptoms such as anxiety.
Fruhling Rijsdijk, a statistical geneticist at King’s College London, was involved in both new studies. We asked her how studying twins can help settle the score between genetic and environmental factors in autism.
Spectrum: What can we learn from twin studies?
Fruhling Rijsdijk: Twin studies give us a handle on how individual differences in the population might be explained by genetic differences. It’s the first step that you would want to take before trying to identify specific genes involved in a certain trait or condition such as autism.