Israeli and NY researchers find evidence autism genetic

For the first time, scientists provide functional evidence that inheriting fewer copies of genes on chromosome #16 leads to autism-like features.

By
October 9, 2011 02:39
3 minute read.
X-ray of a brain

Brain 311 T. (photo credit: Thinkstock/Imagebank)

 
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The neuro-cognitive, developmental disease of autism, whose symptoms appear during the first three years of a child’s life, have for years been thought to involve a number of genes, but there was no concrete proof.

Now a team at Cold Spring Harbor Laboratory (CSHL) in New York, led by an Israeli doing postdoctoral fellowship work on mice, has for the first time provided functional evidence that inheriting fewer copies of genes on chromosome #16 leads to autism-like features.

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Dr. Guy Horev, of the Weizmann Institute of Science in Rehovot, worked at CSHL with Prof. Alea Mills and colleagues on mouse models of autism that they created using chromosome engineering. The study, of which Horev was the first author, has just appeared in Proceedings of the National Academy of Sciences (PNAS).

Autism, or pervasive developmental disorder, is a physical condition connected to abnormal chemistry and biology in the brain and affects the brain’s normal development of social and communication skills. Genes have for years been implicated, as identical twins have a much higher risk than fraternal twins, or siblings, to both have autism.

“Mice with the deletion acted completely differently from normal mice,” said Horev, who is working at Mills’s lab. These mice had a number of behaviors characteristic of autism – hyperactivity, inadequate sleep, difficulty adapting to a new environment and restricted, repetitive behaviors.

“Children normally inherit one copy of a gene from each parent. We had the tools to see whether copy number changes found in kids with autism were causing the syndrome,” added Mills.

In 2007, CSHL Prof. Michael Wigler revealed that some children with autism have a small deletion on chromosome 16, affecting 27 genes in a region of our genomes referred to as 16p11.2.

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The deletion – which causes children to inherit only a single copy of the 27-gene cluster – is one of the most common copy number variations (CNVs) associated with autism.

“The idea that this deletion might be causing autism was exciting,” recalled Mills. “So we asked whether clipping out the same set of genes in mice would have any effect.”

After engineering mice that had a chromosome defect corresponding to the human 16p11.2 deletion found in autism, the researchers analyzed these models for a variety of behaviors, as the clinical features of autism often vary widely from patient to patient, even within the same family. Rodents that had been engineered to carry an extra copy, or duplication, of the 16p11.2 region did not have these characteristics, but instead, had the reciprocal behaviors.

For each behavior, the deletion had a more dire consequence than the duplication, indicating that gene loss was more severe. This might explain why 16p11.2 duplications are detected much more frequently than deletions within the human population, and why patients with 16p11.2 deletions tend to be diagnosed earlier than those with duplications, the team suggested.

The mouse models also revealed a potential link between 16p11.2 deletion and survival, as about half the mice died following birth.

Whether these findings extend to the human population might be answered by future studies that investigate the link between this deletion and unexplained cases of infant death.

The researchers used MRI scans to identify specific regions of the brain that were changed in the autism models, revealing that eight different parts of the brain were affected. Horev and his colleagues are now working to identify which gene or group of genes among the 27 that are located within the deleted region is responsible for the behaviors and brain alterations observed.

They believe their findings on mice will be invaluable for pinpointing the genetic basis of autism and for elucidating how these alterations affect the brain.

Their research could also be used for designing ways to diagnose children with autism before they develop the full-blown syndrome, as well as for designing clinical interventions.

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