A new study carried out in Stanford University found that environmental factors may play an even more important role than genetics in causing autism. Autism is a neuro developmental disorder –an impairment of the growth and development of the brain or central nervous system- characterized by defective social interaction and communication, and by restrictive and repetitive behavior. It first appears during infancy or childhood, and generally follows a steady course without remission. Autism is one of three recognized disorders in what is known as autism spectrum disorders (ASDs).

The number of children diagnosed with autism has increased considerably since the early 1980s. Although the explanation for this increase can be improved diagnosis, the rate of increase is so dramatic as to disregard this as the only cause. Although worldwide the prevalence of autism is estimated in about 1-2 per 100,000 children, the U.S. Centers for Disease Control and Prevention estimate that approximately one on 110 children in the U.S. have some form of autism spectrum disorder (ASD).

Although there is no cure for this condition, there are a few reported cases of children who recovered. Some autistic children have continued to lead highly successful professional lives.

Until a few decades ago, many psychiatrists thought that autism was caused by lack of maternal warmth, a belief that did a lot of harm to the mothers of children affected with this condition. More recently, it was believed that autism had a very strong genetic component. This happened until this new study, that stresses the important of a wide variety of environmental factors.

According to the study, conducted in 192 pairs of twins in California, genetics accounted for approximately 38 percent of autism cases, while different environmental factors were responsible for about 62 percent. The results, which contradict previous studies that suggested that genetic causes were far more important, offer hope for a better control of this condition once specific causes are better defined.

In this new study researchers looked at both identical and fraternal twins drawn form California databases. While identical twins share 100 percent of their genes, fraternal twins share only 50 percent of them. Comparing the rates of autism on both types of twins allowed the researchers to measure the importance of genes versus environment as causing this condition.

The study found that autism or autism spectrum disorders occurred more frequently in identical twins when compared to fraternal twins. Surprisingly, however, a mathematical study of the results strongly suggested that environmental factors were responsible in a greater percentage of cases than genetic ones. This new study confirms similar results reported by University of California scientists in 2009.

Probably dozens if not hundreds of chemicals in the environment are neurodevelopmental toxins, that is, they affect the growth of the brain or central nervous system. Among these environmental toxins are polychlorinated biphenyls (PCBs), brominated flame retardants, pesticides, mercury, lead and several other substances.

In addition to these environmental factors, another recent study has shown a potential association between use of antidepressants during pregnancy and risk of developing autism. The study of more than 1800 children found an adjusted 2-fold increase risk for ASD among mothers who used a type of antidepressant during the year before delivery and a 3-fold increased risk when the antidepressant was taken during the first trimester of pregnancy.

However, as the authors of the study were quick to state, these findings should be taken with extreme caution, since further studies are needed to determine if these studies represent a causal and not a coincidental connection.

These studies on the effect of drugs and environmental factors are extremely important since they show that eliminating those factors can also lead to a dramatic reduction in the number of children affected by autism, a disorder that has serious effects not only on the children but also on the whole family as well.

Dr. Cesar Chelala is an international public health consultant.