Mirror movements 1 is a condition wherein intentional movements made by one side of the body are involuntarily mirrored by the contralateral side. It primarily affects the upper limbs, particularly the hands and fingers. Patients also suffer from pain or cramping during repetitive manual activities. Neurological anomalies include abnormal corticospinal tract decussation, absence of hippocampal commissure, and in some cases, agenesis of the corpus callosum.
The condition has an onset in infancy or early childhood and often persists throughout life. While the movements do not decrease over time, the disorder does not affect a person’s lifespan. The severity of movement varies between individuals, even within families. It is a rare disorder, suspected to affect less than 1 individual in a million live births.
The diagnosis of MRMV1 is confirmed based on clinical findings and molecular analysis of the Deleted in Colorectal Carcinoma (DCC) gene. Treatment is mainly focused on occupational therapy and adjusting the affected individual’s environment to fit their needs. Patients are also advised to refrain from activities that require complex bilateral movement or sustained manual activity.
Mirror movements 1 is an autosomal dominant condition with incomplete penetrance. It is caused by mutations in the DCC gene, which encodes a transmembrane receptor for netrin-1, a chemoattractant for axons. DCC thus plays a role in axon guidance and lateralization during the development of the nervous system. It also functions as a tumor suppressor by inducing cell apoptosis in the absence of its ligand. At least 11 heterozygous mutations in the DCC gene have been implicated in mirror movements 1, including missense variants, deletions and premature terminations.
Monies et al. (2017) outlined the findings of 1000 diagnostic panels and exomes carried out at a next generation sequencing lab in Saudi Arabia. One patient, a 29-year-old female, suffered from slowly progressive adult-onset ataxia. She did not have any cognitive dysfunction and a nerve conduction study was indicative of sensory neuropathy. She also reported a family history of this phenotype. Using a multigene panel for neurological disorders, a heterozygous mutation (c.1423C>T, p.R475X) was identified in exon 9 of the patient’s DCC gene, associated with Mirror Movements 1. Given the atypical presentation of the patient, this case helped in the phenotypic expansion of the disorder.