Understanding the Genetic and Environmental Factors of Autism

A recent study conducted by researchers at King's College London, Karolinska Institutet in Sweden and Mount Sinai in the United States show that understanding the environmental factors of autism are just as important as studying the genetic aspects.

The study examined 2 million children born in Sweden between 1982 and 2006, 14,516 of whom had been diagnosed with an autism spectrum disorder (ASD). The researchers analyzed pairs from family members, including identical and non-identical twins, siblings, maternal and paternal half-siblings and cousins.

Findings showed that children with a sibling with autism are up to 10 times more likely to develop autism.

The study involved two separate measures of autism risk - heritability, which is the proportion of risk in the population that can be attributed to genetic factors; and Relative Recurrent Risk which measures individual risk for people who have a relative with autism.

Previous studies have estimated that having a family member with autism, particularly a sibling, can increase an individual's rate for as much as 80 to 90 percent. However, the study authors believe that this is the first study show how 50 percent of the risk is linked to heritability, while another 50 percent can be explained by non-heritable environmental factors.

Professor Avi Reichenberg, author of the study from Mount Sinai Seaver Center for Autism Research, who led the study whilst at King's College London, notes the following, via a press release: "Heritability is a population measure, so whilst it does not tell us much about risk at an individual level, it does tell us where to look for causes," said professor Avi Reichenberg, author of the study from Mount Sinai Seaver Center for Autism Research, via a press release. "We were surprised by our findings as we did not expect the importance of environmental factors in autism to be so strong. Recent research efforts have tended to focus on genes, but it's now clear that we need much more research to focus on identifying what these environmental factors are. In the same way that there are multiple genetic factors to consider, there will likely be many different environmental factors contributing to the development of autism."

The researchers also assessed individual risk in the general population, showing that around 1 in 100 children are affected by autism. Findings showed that children with a brother or sister with autism are up to 10.3 times more likely to develop autism; 3.3-2.9 times if they had a half-brother or sister with autism; and 2.0 times if they had a cousin with autism. Yet the study showed differences in relative risk between gender.

There were no differences in relative risks between genders. This is the first study to provide such a comprehensive and far reaching analysis of individual risk extended as far as cousins.

"Our study was prompted by a very basic question which parents often ask: 'if I have a child with autism, what is the risk my next child will too?' Our study shows that at an individual level, the risk of autism increases according to how close you are genetically to other relatives with autism. We can now provide accurate information about autism risk which can comfort and guide parents and clinicians in their decisions," said the study author, Dr. Sven Sandin, via the release.

More information regarding the findings can be seen via JAMA.