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Congenital mirror movement disorder (CMM) is a rare disorder characterized by persistent, involuntary movements on one side of the body that mirror intentional movements on the opposite side of the body.[8828][8829][15132] Mirroring movements are common in early stages of life during development, but they typically disappear during childhood when neurologic development of motor pathways is complete. Mirror movements that do not disappear and persist into adulthood are considered abnormal.[15132] In people with CMM, no other neurologic abnormalities are present, distinguishing CMM from other neurologic disorders that cause abnormal mirror movements.[15132] CMM can be caused by mutations in the RAD51 or DCC genes.[8829][15132][15134] In some cases, the cause is unknown, but it is likely that mutations in other, unidentified genes are also responsible for CMM.[8828] The mutations that cause CMM may be inherited from a parent (familial CMM) or may occur for the first time in a person with no family history of CMM (sporadic CMM). Inheritance of familial CMM usually is autosomal dominant but may be autosomal recessive in rare cases.[8828][8829][15132] Not all people who inherit mutations that cause CMM will have the disorder (a phenomenon known as reduced penetrance).[8829] The diagnosis can be made based on the symptoms (a clinical diagnosis) which may be confirmed with genetic testing if a responsible mutation is found.[8829] Management of CMM in childhood may include special accommodations in school (such as allowing extra time to complete work and limiting the amount of handwriting), but it should be made clear to teachers that intellectual disability is not associated with CMM.[8829] To reduce the risk of pain or discomfort in the hands and arms, people with CMM may benefit from limiting complex movements involving both hands and sustained or repetitive hand activity.[8829]
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