A mutation in the RAD51 gene causes congenital mirror movement disorder (CMM), a disease that prevents the hands from moving independently. This gene could enable scientists to better understand the mechanisms underlying manual motor activity.
Congenital mirror movement disorder is a rare disease that is passed from generation to generation. Those affected do not have the ability to perform different gestures at the same time with both hands: When one hand performs a movement, the other hand automatically performs the same movement against the will of the affected person.
In this disease, it is therefore strictly impossible to have a motor activity with two hands like playing the piano. Sometimes these phenomena can be observed in children, but they usually disappear spontaneously before the age of 10, probably due to the maturation of the motor neuron networks. However, in people with this syndrome, the symptoms appear from early childhood and remain unchanged throughout life.
In 2010, researchers in Quebec discovered a gene responsible for the disease by analyzing the genome of members of a large Canadian family. Mutations had been identified in the DCC gene (Deleted in Colorectal Cancer). Following this discovery, the Inserm and CNRS research team, as well as doctors from Paris hospitals, coordinated by Emmanuel Flamand-Roze, therefore searched for mutations in this gene in several members of a French family suffering from the congenital disease of mirror movement: without success. The DCC gene was intact,” explains Emmanuel Flamand-Roze. When we thought we were close to a cure, we had to look for a mutation in another gene,” he adds. His results will be published in the American Journal of Human Genetics.
RAD51, the cause of Congenital Mirror Movement Disorder
Using an approach that combines conventional genetic analysis and what is known as global exome sequencing (a new generation genetic analysis technique that allows the sequencing of all the major parts of the genome), the researchers were able to show that the RAD51 gene is responsible for Congenital mirror movement disorder in a large French family and confirmed this result in a German family suffering from the same disease.
The RAD51 gene was known in the scientific community for its potential role in the development of certain cancers and the phenomenon of resistance to chemotherapy,” explains Emmanuel Flamand-Roze. So we tried to see if it might have another function that could explain the motor symptoms of this disease.
The human motor system is cross-organized, with the left hemisphere of the brain controlling the motor capacities on the right side and vice versa, with a cross-over in the brainstem. By studying the expression of the protein RAD51 during the development of the motor system in rats, the researchers discovered that this gene might be involved in the crossing of the motor pathways connecting the brain with the spinal cord at the brainstem level.
This discovery opens up a completely new field of research to understand the development of the motor system and to better understand the brain mechanisms that control bimanual motor skills. It could shed light on other motor disorders associated with changes in the fine organization of movement, such as dystonia, or on certain genetic disorders of neurological development.