By Denise Mann WEDNESDAY, Oct. 3 (HealthDay News) -- 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. The new findings, which appear in
the Oct. 3 online issue of the New England Journal of Medicine,
dovetail with a similar study published last week in The Lancet.
In the latest study, researchers Joep de Ligt and colleagues at
Radboud University, in the Netherlands, 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 t