[Research] Autism: Environmental factors vs. genetics

[Bernard]

Environmental factors play a more important role in causing autism than previously assumed and, surprisingly, an even larger role than genetics, according to a new study out of UCSF and Stanford that could force a dramatic swing in the focus of research into the developmental disorder.

The study, published in Monday's issue of the Archives of General Psychiatry, looked at 192 pairs of twins in California and, using a mathematical model, found that genetics account for about 38 percent of the risk of autism, and environmental factors account for about 62 percent.

Previous twin studies had suggested that autism was highly inheritable, with genetics accounting for roughly 90 percent of all cases worldwide. As such, much recent research into autism has focused on tracking down the genes and unlocking the complex genetic codes that are associated with autism.

"We're not trying to say there isn't a genetic component - quite the opposite. But for most individuals with autism spectrum disorder, it's not simply a genetic cause," said Neil Risch, director of the UCSF Institute for Human Genetics, who designed the study.
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Twin studies often are used to distinguish between environmental and genetic influences on medical disorders. Identical twins share nearly 100 percent of their genes, and fraternal twins share about half of their genes. In both cases the siblings' early developmental environment - both in the womb and after birth - are very similar.

Several small twin studies in the past decade looked at how common it was for twin siblings to share an autism diagnosis, and results of those studies placed genetics as the primary cause of autism. But some scientists believe that those studies weren't large enough to note the differences in shared diagnoses rates between identical and fraternal twins.

The new study is the largest, and the most diverse, to look at twins. Of the 192 pairs of twins in the study, 54 were identical and 138 were fraternal. At least one sibling in each pair was autistic, and every child was interviewed by researchers to confirm that diagnosis.

If autism was entirely a genetic disease, then scientists would expect that if one identical twin had the disorder, the other twin would too. And they'd expect that among fraternal twins, if one twin had the disorder, then the other would have a slightly higher risk of developing autism than the general population. Previous studies have indicated that if one non-twin sibling has autism, other siblings have about a 5 percent chance of developing the disorder.

But in the study, researchers found that only about 60 to 70 percent of the identical twins had dual autism diagnoses - lower than expected - and 20 to 30 percent of the fraternal twins had dual diagnoses - much higher than anticipated.

Those rates, along with the expected rates scientists would find if autism was entirely genetic or entirely environmentally caused, were plugged into a mathematical equation, and researchers determined that only about 38 percent of autism risk could be tied to genetics.

"The rates for the (fraternal) twin pairs were so high, I retyped all of the results because I thought we'd mixed them up," said Dr. Joachim Hallmayer, an associate professor in psychiatry at Stanford and lead author of the study. "This draws attention to the environment, and to the possibility that shared environmental factors play a bigger role than we had previously assumed."

Several scientists said they expect the new study to start shifting research toward early environmental factors, in particular prenatal conditions for developing fetuses.
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More: http://www.seattlepi.com/news/articl...ng-1452985.php

[hootie]

Not surprised by the results...too many chemicals in the environment is eventually going to take its toll on the body...especially a developing one.

There can not be a genetic epidemic!!! Those researchers are barking up the wrong tree and wasting a lot of $$$ telling us something we already can figure out with a little common sense.

The moms have been saying this all along. I guess it is good to have the science to back it up...

[RobinN]

There can not be a genetic epidemic!!!

The moms have been saying this all along. I guess it is good to have the science to back it up...

So very true! Finally what we parents have been saying is getting attention.

[Endless]

I wonder if the age of the father is considered environmental or genetic? Fathers in their 40's have a 500% greater chance of having an autistic child than a father in his 20's.

Correlation doesn't mean causation. Maybe it's an environmental factor that is found more often in the home/life of men more often as they increase in age.

[hootie]

I would say environmental...they are exposed to all the toxins too...all those chemicals can't be good for (old) sperm...