Congenital mirror movement disorder
Congenital mirror movement disorder is a rare condition characterized by involuntary, mirrored movements on one side of the body when the opposite side performs an intentional action.
Overview
Congenital mirror movement disorder is a condition in which intentional movements of one side of the body are mirrored by involuntary movements of the other side. For example, when an affected individual makes a fist with the right hand, the left hand makes a similar movement. These movements primarily affect the arms, and the hands and fingers are always involved. This pattern is present from infancy or early childhood and usually persists throughout a person's life.
While the involuntary movements are typically less pronounced than the corresponding voluntary movements, they can cause difficulty with daily activities that require different movements in each hand, such as typing. Prolonged use of the hands may lead to discomfort or pain. In some cases, individuals may also have partial or complete absence (agenesis) of the corpus callosum, the tissue connecting the two halves of the brain.
Causes & Risk Factors
The disorder is caused by variants in at least three genes: DCC, RAD51, and NTN1.
- DCC and NTN1: These genes provide instructions for proteins (netrin-1 receptor and netrin-1) that act like a lock and key to direct the growth of axons in the developing nervous system. When these proteins are impaired, axons do not develop properly, causing movement signals from each half of the brain to be transmitted to both sides of the body.
- RAD51: This gene is involved in DNA repair and the development of nervous system functions that control movement. Impaired RAD51 protein function is thought to disrupt early nervous system development.
In some cases, the cause of the disorder remains unknown.
Inheritance
Congenital mirror movement disorder is most commonly inherited in an autosomal dominant pattern, meaning one copy of the altered gene is sufficient to cause the disorder. Some individuals with the altered gene may never develop the condition, a phenomenon known as reduced penetrance. In very rare cases, the condition may be inherited in an autosomal recessive pattern, requiring two copies of the variant gene.