Genetic breakthrough: identification of a disorder causing intellectual disability | News

Scientists have discovered the genetic root of a disorder that causes intellectual disability, which they say affects up to one in 20,000 young people. And they hope their discovery will lead to a new diagnosis that can help answers to families.

People with the condition have a host of problems, including short stature, small heads, seizures and low muscle mass, said researchers who published their findings Friday in the journal Nature Medicine.

“We were struck by how common this disorder was” compared to other rare diseases linked to a single gene, said Ernest Turro of the Icahn School of Medicine at Mount Sinai, lead author of the study.

Syndromes like these can go unnoticed because the traits are sometimes so subtle that doctors can't recognize them just by looking at patients, said Dr. Charles Billington, a pediatric geneticist at the University of Minnesota who has not participated in the study.

“We certainly didn’t necessarily have a name for it,” he said. “We are learning more about these syndromes that we only recognize once we see the cause.”

The researchers said the mutations occurred in a small “non-coding” gene, meaning it does not provide instructions for making proteins. So far, all but nine of the nearly 1,500 genes known to be linked to intellectual disability in general are protein-coding genes. Until now, most large genetic studies have used sequencing technology that typically leaves out genes that don't code for proteins.

This study used more comprehensive 'whole genome' sequencing data from 77,539 people enrolled in the UK's 100,000 Genomes Project, including 5,529 with intellectual disabilities. The rare mutations researchers found in the gene, called RNU4-2, were strongly associated with the risk of developing intellectual disability.

The discovery “opens the door to diagnostics” for thousands of families, said study author Andrew Mumford, research director of the genomic medicine service at NHS South West England.

More research is needed, Mumford said. How the mutation causes the disease remains unclear and there is no treatment. But Billington said labs should be able to offer testing for this disease relatively quickly. And researchers said families should be able to come together and support each other — and know they're not alone.

“It can be incredibly comforting,” Mumford said.