Washington, July 11 : An international team of researchers has identified six genes that, when mutated, contribute to autism with the help of Middle Eastern families.
Up till now, the hunt for gene mutations that contribute to autism has proceeded slowly, largely because autism encompasses a spectrum of diseases.
But with the latest study, Howard Hughes Medical Institute investigator Christopher Walsh, in collaboration with scientists and physicians in the United States, Turkey, Saudi Arabia, Pakistan, and Kuwait, have pinpointed autism genes using a new strategy.
By focusing on large families in which both parents share a recent ancestor, Walsh and his colleagues were able to hone in on rare mutations that had remained elusive in previous studies.
Autistic children share three key traits: they're slow to develop language, they are poor at social interactions, and they repeat stereotyped behavior over and over. But that's where the similarities end; some forms of autism are subtle, whereas others devastate every aspect of functioning.
This variation is evidence of the wide variety of genes that can contribute to the disorder, Walsh says, and makes finding those genes difficult.
"At the moment, we understand the genetic causes of 15 to 20 percent of autism. The remaining 80 percent remain unexplained," Walsh said.
In the study, Walsh collaborated with researchers from the Middle East, where families are typically larger. The average of six children per family-versus two or three in the United States and Europe-makes it much easier to compare genes within a family.
Walsh and his colleagues took another step to make finding autism genes easier: they specifically targeted families in which the mother and father shared a recent ancestor.
The researchers studied 88 such families, from eight countries: Jordan, Saudi Arabia, Kuwait, Oman, Pakistan, Qatar, Turkey, and the United Arab Emirates.
In five of those families, they found that large segments of individuals' genomes were missing. While family members who retained one functional copy of these segments did not have autism, those with both copies missing had the disorder.
Many of these deletions inactivated genes involved in learning, Walsh said.
Specifically, they help nerve cells carry out the physical changes to their synapses that underlie learning and the formation of new memories.
Walsh said that in a developmental disorder like autism, that was an important find.
The study has been published in the journal Science.