Genes Linked to Retardation Not Inherited
Testing found new mutations only in people with the condition, not their parents.
New research adds to a growing body of evidence suggesting that severe intellectual disability is caused by random genetic mutations that are not passed down from parents.
Severe intellectual disability, also known as nonsyndromic mental retardation, is the most common form of mental retardation. Children or adults with the condition have no physical abnormalities, but have IQs of less than 50. It affects up to 2 percent of children worldwide.
In the latest study, researchers used a sophisticated type of gene screen called exome sequencing on 100 people with severe intellectual disabilities and their unaffected parents.
The investigators found that there were gene mutations in the patients' DNA samples, but they were new ones that were not passed down from their parents. All in all, they identified 79 genetic mutations in 53 patients, many of which had never been seen before. They confirmed their findings in another group of 765 people with intellectual disability.
The new technology allows researchers to dig deeper into genes. This removes the idea of looking at a candidate gene or region and opens it up to look at everything. We are going from a 10,000-foot view to street-level view and we are seeing gene changes that we have never seen before.
The new findings may help pave the way for screening tests or new therapies that target these genes. These screens would be something that we could potentially do in early pregnancy, but we are a long way from that.
These are exciting times in medical genetics, and exome sequencing is revolutionizing the field. The new study shows how the technology can be used successfully in a diagnostic setting for patients with severe intellectual disability.
Recent research suggesting that risk of intellectual disability is not passed down from parents should be largely reassuring.
These new gene screens do identify a host of mutations, and the challenge is trying to determine which ones play a causative role and which ones don't.
Source: U.S. Dept. of Health & Human Services
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