Myoclonus-dystonia (M-D) is a movement disorder characterized by a combination of rapid, brief muscle contractions (myoclonus) and/or sustained twisting and repetitive movements that result in abnormal postures (dystonia
Myoclonus-dystonia (M-D) is a movement disorder characterized by a combination of rapid, brief muscle contractions (myoclonus) and/or sustained twisting and repetitive movements that result in abnormal postures (dystonia). Onset of myoclonus is usually in the first or second decade of life. The myoclonic jerks typical of M-D are brief, lightning-like movements that most often affect the neck, trunk, and upper limbs with less common involvement of the legs. Dystonia is observed in more than half of affected individuals, but is only rarely seen without myoclonus. Affected individuals can have focal or segmental dystonia, presenting as cervical dystonia and/or writer's cramp. Most affected adults report a dramatic reduction in myoclonus in response to alcohol ingestion. The most prominent non-motor features have been psychiatric problems including depression, anxiety, obsessive-compulsive disorder (OCD), personality disorders, addiction, and panic attacks.
The diagnosis of myoclonus-dystonia is based on clinical findings, family history, absence of other neurologic deficits, and normal neuroimaging studies. In general, all laboratory tests are normal in individuals with M-D. Abnormal liver function tests may be the result of chronic alcohol use.
Myoclonus-dystonia is inherited in an autosomal dominant manner. Mutations in the SGCE gene (7q21) are identified in approximately 30-50% of individuals with familial M-D and 10-15% of simplex cases. Simplex and familial cases without identifiable SGCE mutations have been reported, suggesting locus heterogeneity. Reduced penetrance on maternal transmission of the disease allele has been observed, s