New Clues on Genetic Causes of Autism

June 8, 2011 -- Genetic mutations not inherited from parents appear to explain some cases of autism, new research suggests. And the mutations may number in the hundreds.

While the new research is a step forward, it is a small puzzle piece. "It could explain up to 2% of all autism cases," says researcher Stephan J. Sanders, MD, a postdoctoral research associate at Yale University's Child Study Center.

Even so, he says the new research -- reported as a trio of studies in the journal Neuron -- provides a solid foundation to a better understanding of the biology of the disorder, eventually leading to better treatments.

In the new research, scientists also found new clues about why boys seem to be more vulnerable to the disorder than girls.

''In combination with some other research studies, this new research shows pretty clearly there is indeed a strong genetic component to autism, and that the individual genes can be identified," say Alan Packer, PhD, associate director for research at the Simons Foundation. It funds autism research and provided the sample populations studied in the new research. 

About one in 110 U.S. children has autism or autism spectrum disorder, the neurodevelopmental disorders marked by impaired communication, social interaction problems, repetitive behaviors, and other problems.

Genetic Causes of Autism: Trio of Studies

In two of the new studies, researchers analyzed more than 1,000 families who have one autistic child and unaffected siblings. They evaluated their DNA from blood samples. The researchers used a highly sophisticated technique that can detect duplications or deletions of one or more sections of DNA.

These duplications or deletions are called copy number variants or CNVs. If they occur at random, or sporadically, and aren't inherited, they are known as de novo CNVs.

Some CNVs ''are normal parts of being human," Sanders tells WebMD. "It's very difficult to find the ones that matter. We looked for ones that were new in the child.''

They found more new CNVs in autistic children than in unaffected children, which they expected.

They zeroed in on many regions linked with these rare sporadic mutations, Sanders says, confirming previous research on which areas matter. "Basically five regions really stand out now," he says.

These include areas of chromosome 7, 15, 16, 17 and Neurexin 1.

The team estimates ''there are 130-234 CNV regions that could be linked with autism," he says.

The researchers also found that the long arm of chromosome 7, a region associated with Williams syndrome, a genetic disorder in which people are highly social and overly friendly with strangers, may also be associated with autism.

"For a long time it has been known if you have a deletion there, it causes Williams syndrome," Sanders says.

They found the children with autism were more likely to have duplications in this region.

So it appears having a duplication may make you less social -- one of the characteristics of autism.