Researchers have linked mutations in a specific gene to what appears to be a distinct subtype of autism. Their findings, published in Cell, represent an important first step in individualizing diagnosis and treatment of autism spectrum disorder (ASD).
Past research has implicated hundreds of gene mutations as increasing the risk that a child will develop autism. Most of these gene changes increase autism risk only slightly. A few almost always lead to autism but as part of a larger syndrome – such as Fragile X and Angelman’s – with autism as just one symptom.
As such, the new findings may represent the first clear-cut case of a gene specific to an autism subtype.
"This will be a game changer in the way scientists are researching autism," says lead author Raphael Bernier, clinical director of the Autism Center at Seattle Children's Hospital. Researchers at 13 institutions were part of Dr. Bernier’s team.
In their study of 6,176 individuals with ASD, the researchers found 15 who had a mutation in the CHD8 gene. All 15 shared distinctive physical characteristics and health issues. They looked strikingly similar, with broad foreheads and wide-set eyes. They also shared a history of gastrointestinal problems (severe constipation) and disturbed sleep. Sleep problems and constipation are common but not universal among individuals with autism.
The researchers did not find the mutation in tests of nearly 9,000 individuals not affected by autism. When functioning properly, CHD8 regulates the structure of DNA. How its disruption results in autism is not yet understood.
The mutation likely affects less than 1 percent of those with autism. So its importance lies in being the first to be linked to what may be a specific subtype of autism. Autism is currently diagnosed almost entirely by observation of behavior – without regard to what’s causing the disorder in a particular individual.
Autism researchers have long suspected that there is not one autism, but rather many autisms – each with its own underlying biology. Increasingly, genetic research is aimed at understanding these underlying mechanisms and developing individualized treatments based on the findings.
Further insights from zebrafish
In the new study, the researchers further investigated the Cdh8 gene by blocking its expression in zebrafish embryos. The fish developed unusually large eyes, and their digestive system took much longer to empty. The lining of their guts also had around half the normal amount of nerve cells.