California Autism Twins Study - Suggested Future Research Idea

A new study of autism has produced some interesting findings that birth environment plays a more significant roll than previously thought in impacting whether a child gets autism. The NY times had a good article on the study and here is another similar piece.

The study "Genetic Heritability and Shared Environmental Factors Among Twin Pairs With Autism" published in the Arch Gen Psychiatry looked at autism rates for siblings of fraternal and identical twins of kids with autism. While it has widely been know that hereditary factors play a roll this study finds that environmental factors before and during pregnancy, all of which a twin would experience at the same way as his or her sibling, play a significant roll as well. The part parents will find unsatisfying is they study does not tell us which of many environmental factors (some of which people can control and others you can't) really makes a difference. Some of the factors which the study suggests could play a roll include age of the mother, birth weight, maternal infections, and medications taken by the mother.

One possible study design that I think would yield some telling findings which could be conducted in a manner somewhat similar to this one would be to recruit two groups of families with autistic children which all have younger siblings. Then you would specifically look for families that moved into a new house in a new neighborhood or even new state after the autistic child was born and compare the rates of autism between the younger siblings. The reason that this difference would help isolate the environmental factors is that when mom moves, certain factors would remain the same while others would change. The kids who's parents moved would be exposed to different air quality both indoor and outdoor, different water qualify, different indoor toxins that could possibly expose the child from paint or other chemicals. This study would actually be easier to find volunteers for because twins with autism are still fairly rare but autistic children with younger siblings are far more common.

The hard thing to compare with studies like this (and I know researchers try) is what environmental conditions people are exposed to because it is impossible to really study what water someone drinks, what air they breath, what pesticides they are exposed to because these things change every day. While there is an increase in prevalence in autism in the US, luckily it is not so common yet so the necessary combination of environmental factors combined with hereditary factors that leads to autism are still relatively rare.

If such a study were conducted, you would of course expect that both groups would have a higher prevalence of autism in the sibling than a the general rates of autism. This is well know because there is a significant genetic factor. However if there were not any differences in the rates for siblings who's mothers moved/ vs mother's who did not, if the sample size were large enough you could reasonably conclude that those types of environmental factors that typically change when you'd move, do not significantly impact rates of autism.

One criticism of my suggested approach is that you could never control for all the other factors that would vary from one birth to the other that could impact likelihood of autism, maybe mom switched to an organic diet, gained weight, took over the counter medication during pregnancy, put new paint on her walls, got a new job, there are millions of factors. If the sample size were large enough, these factors would all even themselves out and there is not any likely corrialtion with any of these factors and moving.