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Summary Severe intellectual disability is the most common form of mental retardation.
More than half of the cases of severe intellectual disability are the result of random genetic mutations that are not passed down from parents, researchers from Switzerland and Germany report.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 kids worldwide. The new study, which appears online Sept. 27 in The Lancet, suggests that many of the gene variants associated with the condition show up for the first time in the affected children.The majority of patients with severe intellectual disability are due to gene mutations that are not present in the parents, said study author Dr. Anita Rauch, a researcher at the Institute of Medical Genetics in Zurich. In the majority of cases, the recurrence risk within the family is low, which is usually a big relief for the parents and encourages them to have further children.Researchers from the German Mental Retardation Network used a new gene sequencing technique to look for mutations in 51 children with unexplained intellectual disability and their unaffected parents. According to the report, children with intellectual disability carried a significantly higher number of potentially disease-causing genes than those without the disorder. New mutations in 11 known and six new candidate genes were estimated to cause intellectual disability in up to 55 percent of the children, the study authors reported.In the future, Rauch said, identification of subgroups of patients with a certain defect may soon lead to a better understanding of the respective natural course, which may then lead to a better disease management by earlier recognition of accompanying complications. As it stands, children and adults with nonsyndromic mental retardation are treated only with supportive education and supportive treatment of complications such as epilepsy, she added.
