In Autism, Genes Do not Tell the Whole Story: Environmental Factors Have to Be Taken More Seriously

Environmental Factors Have an Important Say in the Development of Autism

For a long time, scientists wondered about the reason behind the development autism. It wasn’t that long ago that mothers were held responsible for having an autistic child. These "refrigerator mothers" were accused of not showering enough love on the child, which developed autism as a result of neglect — or so the story went. Thankfully, this idea was debunked soon enough.

Later, factors like a person's genetic makeup, parental age, multiple pregnancies, low birth weight and exposure to medications or maternal infection during pregnancy were associated with the condition. Prior research studies showed that almost 90 percent of the cases of autism could be linked to inherited genes. But, this did not explain the rapidly increasing number of children suffering from autism. Our genes do not evolve so fast, scientists said. One study, which involved the largest number of twins, in which at least one in each pair was diagnosed with autism, has confirmed the role of genes in the disease. But, in what can be termed as a major breakthrough, it has been found that it is the environmental factors that play a very important role in the development of the condition, too — almost 62 percent cases were linked to these factors as compared to just 38 percent of cases believed to be purely genetic.

It is the Interplay between the Environmental Factors and the Genetic Factors that Leads to Autism

According to Joachim Hallmayer, the lead author of the study, which was published in the July 4, 2011, issue of the Archives of General Psychiatry, the findings have surprised many. The research shows that the role of environmental factors was grossly underestimated over the years. He feels that it is the interplay between the environmental and the genetic factors that leads to autism.

The study was conducted on 192 pairs of twins who received services for developmental disabilities, from the diverse population of California. It included 54 pairs of identical twins and 138 pairs of fraternal twins, wherein at least one child from each pair had autism. The sets of twins then underwent standardized diagnostic tests to confirm the diagnosis of autism.

The rate of autism was compared between the identical twins, who share all their genes, and fraternal twins, who share a much lower 50 percent of their genes. Each pair shared their environment from conception to childhood, and this is why twin studies can be so insightful. The scientists employed a mathematical model to calculate the precise genetic and environmental contributions to the risk of developing autism spectrum disorder. The environmental contribution to the condition was found to be much higher than expected. Moreover, factors like the ages of the twins' parents, years of parental education, ethnicity, difference in birth weight between twins and gestational age at birth were not found to have any impact whatsoever in the development of autism.

What remains to be investigated is the type of environmental factors that could affect autism. Since the condition is sometimes apparent even in very small children, there are strong possibilities that these environmental factors exert themselves during pregnancy itself. According to Lisa Croen, a co-author on the study, the events that happen during pregnancy need to be explored in depth, to find the environmental factors that lead to autism.