Genes Linked to Retardation Not Inherited, Radboud University Study

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.