Intellectual Disability Is Caused by Spontaneous Mutation

Congenital intellectual disability, which is not associated with a known disease syndrome, is often – so the results of exome ­sequencing – caused by spontaneous mutations in the genome of those affected. Since the mutations are thus not inherited, there is low risk of recurrence in another pregnancy.

Severe congenital intellectual disability, which is not associated with a known disease syndrome such as Down syndrome, is caused to a high percentage by new mutations in the genome of the child and is not inherited from the parents to the child. This is the result of a study by researchers from the Institute of Human Genetics, Helmholtz Zentrum München, which they carried out together with partners from the network ‘Mental Retardation’ in the National Genome Research network (NGFN) and with researchers from the Universities of Erlangen, Essen and Zurich.

To this end, the scientists studied the genomes of 51 patients who were affected by congenital intellectual disability and the genomes of their parents. Tim Strom and Thomas Meitinger of the Institute of Human Genetics carried out exome sequencing for the mutation analyses in which selectively the DNA segment was investigated that encodes proteins and other functional products. In comparison to a control group, they identified in the genomes of the patients a significantly higher number of point mutations and small insertions and/or deletions.In particular, the number of mutations leading to significant damage of the respective protein was increased.

The mutations were found in many different genes, and only in a few genes did the researchers find new mutations in more than one person. The authors of the study
conclude that a large proportion of severe congenital intellectual disability is probably caused by new mutations. With the aid of exome sequencing, intellectual disability will be able to be diagnosed much faster and more easily.

The scientists assume that in the future, the method will become a standard procedure. The good news for the affected parents is that in future pregnancies there is only a slight risk of having a child with an intellectual disability.

Intellectual disability (ID) affects about two percent of the ­population. Although most cases have an underlying genetic cause, to date only a few genetic defects have been identified.