Further Genetic Causes of Mental Retardation Discovered
| A broken chromosome in a 16-year-old patient gave a group of Heidelberg scientists an important clue |
Here Professor Gudrun Rappold and her team examine the genetic factors of mental disability. One of the patients at the institute is 16-year-old Sabine (name changed by the editorial staff).
Sabine’s development is severely retarded. She cannot speak or take care of herself, has recently become afflicted with epileptic seizures, and her backbone is highly distorted. Chromosome Cleavage Site Discovered
The examination of her DNA gave the researchers decisive clues to the cause of her mental disability. The scientists observed that a part of Sabine’s chromosome 3 had broken off. This fragment had fused with a different chromosome. Geneticists call this type of chromosome defect ‘translocation’.
Professor Rappold and her colleague Volker Endris had a very early suspicion that the chromosome breakage could have something to do with Sabine’s handicap. Mr. Endris thus had a closer look at chromosome 3.
As a result, it could be determined that because of the chromosome breakage, a gene had been destroyed that is located precisely at the site of fracture. This gene contains the blueprint for a protein called MEGAP (MEntal disorder associated GAP protein). The researchers assumed further: if a faulty MEGAP was the cause of Sabine’s mental handicap, this gene could be malfunctioning in other affected persons as well. So they examined other patients. Originally, they limited themselves to people who suffer from the so-called 3p deletion syndrome. These people lack a part of chromosome 3.
The findings confirmed the suspicion. In all twelve patients with 3p deletion syndrome, the MEGAP had been completely lost together with the missing piece of chromosome 3.
In further experiments, the scientists from Heidelberg could prove that MEGAP is very important for the development of the brain and intellectual capacity. Apparently, the gene regulates the connection of nerve cells in the brain.
An understanding of the medical model of mental retardation could be the basis for future therapies.
