SNP Shot: Genomic Insights

Myoclonus-dystonia is a movement disorder primarily affecting the neck, torso, and arms. It is characterized by quick, involuntary muscle jerks or twitches known as myoclonus. Approximately half of those affected also develop dystonia, which involves involuntary muscle contractions that lead to abnormal postures. In myoclonus-dystonia, dystonia commonly affects the hands, resulting in writer's cramp, or the neck, causing torticollis (head turning).

The movement issues typically begin in childhood or early adolescence with the onset of myoclonus. In most instances, these movement problems remain stable throughout life. Some adults find that alcohol consumption temporarily reduces myoclonus, which may lead to self-medication and, consequently, alcohol use disorder.

Individuals with myoclonus-dystonia are at an increased risk of developing psychological disorders such as depression, anxiety, panic attacks, and obsessive-compulsive disorder (OCD).

Inheritance:

When the genetic cause of myoclonus-dystonia is known, it follows an autosomal dominant inheritance pattern. This means that only one copy of the mutated gene is necessary in each cell to cause the condition. When the underlying cause is unknown, the inheritance pattern is unclear. If the condition is caused by mutations in the SGCE gene, it is only expressed when the mutation is inherited from the father.

Typically, individuals inherit one copy of each gene from each parent. While both copies of most genes are active in all cells, a small number of genes have only one active copy. For some, the active copy is the one inherited from the father (paternal copy), and for others, it's the copy inherited from the mother (maternal copy). This difference in gene activation based on parental origin is known as genomic imprinting.

Because only the paternal copy of the SGCE gene is normally active, myoclonus-dystonia occurs when the paternal copy of the SGCE gene is mutated. Mutations in the maternal copy usually do not cause health issues. Rarely, individuals who inherit an SGCE gene mutation from their mothers will show symptoms of myoclonus-dystonia. It is not fully understood why the normally inactive gene copy becomes active in these rare cases.

Mutations in other genes associated with myoclonus-dystonia are not subject to imprinting, and thus, mutations causing the condition can be inherited from either parent.