Gene variant puts boys at higher risk of severe autism

May 20th, 2009 - 1:07 pm ICT by IANS  

Washington, May 20 (IANS) The most severe form of autism targets boys four times more often than girls, thanks to a gene variant called CACNA1G.
A variant is a gene that has undergone subtle changes from the normal DNA yet is shared by a significant portion of the population.

If the entire spectrum of autism disorders, such as the milder Asperger syndrome is included, then boys are diagnosed 10 times more often than girls.

Autism is a complex brain disorder that strikes in early childhood. The condition disrupts a child’s ability to communicate and develop social relationships and is often accompanied by acute behavioural challenges.

“This is a strong finding,” said Stanley Nelson, professor of human genetics at the David Geffen School of Medicine at the University of California Los Angeles (UCLA).

“No one has scrutinised the role that CACNA1G plays in autism,” he added.

“We found that a common form of the gene occurs more frequently in the DNA of families that have two or more sons affected by autism, but no affected daughters,” he explained. “Our study may explain why boys are more susceptible to the disorder than girls.”

Nelson and his colleagues zeroed in on a region of Chromosome 17 that previous studies have tied to autism. The research team scoured the DNA of 1,046 members of families with at least two sons affected by autism for common gene variants.

The researchers used tools of the Human Genome Project to scan thousands of variants across all genes in the suspicious region of the chromosome and to pluck out the most common forms.

“We wanted to identify what was happening in this region of Chromosome 17 that boosts autism risk,” said Nelson. “When the same genetic markers kept cropping up in a single region of the DNA, we knew we had uncovered a big clue.”

The researchers traced the genetic markers to CACNA1G, which helps move calcium between the cells. They discovered that the gene has a common variant that appears in the DNA of nearly 40 percent of the population.

“This alternate form of CACNA1G consistently increased the correlation to autism spectrum disorder, suggesting that inheriting the gene may heighten a child’s risk of developing autism,” observed Nelson.

“This variant is a single piece of the puzzle,” he said. “We need a larger sample size to identify all of the genes involved in autism and to solve the whole puzzle of this disease.”

The UCLA team’s next step will be to sequence the gene in people who possess the altered variant in order to identify the exact change that increases autism risk. These subtle variations offer potential markers for the real mutation causing greater susceptibility to the disease.

The Centres for Disease Control and Prevention report that one in 150 American children is diagnosed with an autism spectrum disorder. The diagnosis of autism has expanded tenfold in the last decade, said an UCLA release.

These findings were published in Molecular Psychiatry.

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