DNA Scans Help Pinpoint Causes of Mental Retardation

Sequencing the genomes of 100 individuals with mental retardation with no known cause yielded genetic answers for 16 of them, a study found, suggesting the technique may help diagnose and aid in treatment.

While more than 400 genetic mutations are known to cause intellectual disability, they are responsible for less than half of the cases, said Han Brunner, a study author and head of human genetics at Radboud University Nijmegen Medical Centre in the Netherlands. The research is published today in the New England Journal of Medicine.

The study shows how gene sequencing can improve diagnosis in patients with mental disabilities, many of whom never learn the cause. Knowing the genetic origin can help patients and families understand the prognoses and may lead to specific treatment options, the authors said in the study.

“Half of the children and adults with intellectual disability never have an explanation of why they are retarded -- that’s a big problem,” leading many parents on a quest to numerous doctors looking for answers, Brunner said in a telephone interview. “This is what people call the diagnostic odyssey, and people can put that to rest,” by using genetic sequencing, he said.

Researchers scanned the DNA of children with mental retardation, defined as having an IQ of less than 50, as well as their parents, and looked for differences. While all children have some mutations, few lead to intellectual disability, Brunner said. Once the culprits are known, it can help direct some therapies or dietary changes.

“We had two cases where the type of mutation would suggest that you might try a treatment for a metabolic disorder, and another with epilepsy,” he said.

Diet Effect

For instance, patients with a mutation in the PDHA1 gene would benefit from a ketogenic diet, which is high in fat, and those with SCN2A mutation should avoid sodium-channel blockers to better control their epileptic episodes and improve cognitive function, according to the study.

The research, funded in part by the European Union, demonstrates how the quickening pace of gene sequencing technology may lead to wider use in the clinic to help patients, said Heather Mefford, assistant professor of pediatrics at the University of Washington in Seattle.

The technology used in the study is called exome sequencing and looks at the 1 percent of the DNA containing genes that create proteins. The researchers used equipment from Carlsbad, California-based Life Technologies Corp. to perform the sequencing.

“Previously, you might test one or two genes. Or more recently, a panel of genes,” Mefford, who wrote an accompanying editorial to the study, said in a telephone interview. That approach could take weeks or months and not lead to any answers, she said. “This test allows us to look at all the genes at once.”

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