The discovery was made through DNA research in several families in which only males are afflicted with a mental handicap. In such families, defects appear on the X-chromosome (thus the name X-Linked Mental Retardation). Males have only one version of the X-chromosome. Females have a reserve copy, through which defective information can be masked.
2 - 3% of the population has a mental handicap
Mental handicap occurs in 2 - 3% of the population. The handicap can be attributed to external factors, such as a deficiency in oxygen at birth, or to defects in the DNA. When the cause is genetic (hereditary), exact identification of the defect is crucially important for providing the patient with the proper medical support or for assessing the risk involved for couples with child wish. Recent estimates are that a defect on the X-chromosome is the cause in about 12% of the patients. However, in over half of the XLMR patients, the responsible gene has not yet been identified. This research makes a contribution toward filling this gap in our knowledge.
Source: VIB (the Flanders Institute for Biotechnology)