One statement in the abstract may be misleading. The author says that: “Autism heritability was 50%, suggesting that environmental influence contributed the other 50%.” In fact, that’s not quite right. The fact that heritability is 50% does not mean that all the remaining variance is environmental. There are often contributing factors in any disease with genetic variance that further add genetic influence. For example, we know that CHD has substantial direct genetic variance. However, it is also true that other factors contributing to this disorder have heritable variance. Examples are hypertension and cholesterol levels. The genetic contributions of these factors effectively add to the genetic for CHD above and beyond its basic heritability. In addition, gene-environment interactions typically add independent variance to the causal model for the disease. If autism is also subject to additional, contributing factors and to gene-environment interaction, which is likely, then the 50% direct genetic contribution does not mean that all the remaining variance is environmental.
Genes and Environment Play Equal Roles in Autism — Physician’s First Watch
Genes and Environment Play Equal Roles in Autism
By Kelly Young
Genetic and environmental factors appear to be equal contributors to autism spectrum disorders, according to a JAMA study.
Using Swedish registries, researchers studied 2 million children who were siblings or cousins. During follow-up, nearly 15,000 were diagnosed with autism spectrum disorders (ASD).
The risk for autism by age 20 increased with increasing genetic relatedness. For example, an identical twin had 150 times the relative risk for an ASD if the other twin was diagnosed, while the relative risk for cousins was 2. Autism heritability was 50%, suggesting that environmental influence contributed the other 50%.
Editorialists conclude that this study "supports appreciation of the importance of genetic factors in ASD and adds substantial impetus to the growing attention to environmental influences in ASD etiology."