Dystonia, Focal, Task-Specific

Description

Focal dystonia, the most common form of dystonia, is often task-specific and referred to as FTSD. Specific learned motor tasks, such as writing or playing a musical instrument, can trigger muscle spasms and interfere with performance while other actions are unaffected. FTSD has a frequency of 1 in 3,400 in the general population but increases to 1 in 200 among musicians (Pullman and Hristova, 2005).

Clinical Features

Schmidt et al. (2006) reported 3 unrelated families in which the proband presented with musician's dystonia: 1 pianist and 2 guitarists. All probands had 2 or 3 family members with other forms of focal dystonia, mainly writer's cramp and 1 case of 'handicraft' dystonia while threading needles. Inheritance in all families was consistent with autosomal dominant. All but 1 affected individuals had onset of dystonia in the third or fourth decade. Two affected family members were professional musicians, but had only writer's cramp and no musician's dystonia. Conversely, 1 of the probands had both musician's dystonia and writer's cramp. The disorder was triggered by increased practice in about half of the affected individuals. All had an upper limb dystonia, and none carried common DYT1 mutations (TOR1A; 605204). Schmidt et al. (2006) concluded that musician's dystonia is not necessarily a sporadic condition and that there is a genetic contribution to focal task-specific dystonia with phenotypic variability, including musician's dystonia.

Inheritance

Schmidt et al. (2009) gathered information on families of 28 unrelated individuals with musician's dystonia, 14 of whom reported a positive family history of focal dystonia. The age of the probands ranged from 27 to 74 years, and most were German. Twenty-four patients (86%) had upper limb dystonias, and 4 (14%) had embouchure dystonias affecting the mouth. The age at onset of dystonia ranged from 16 to 66 years. Nineteen (20%) of 97 examined relatives were found to have dystonia, including 8 with musician's dystonia, 9 with FTSD, and 2 with other dystonias, and 5 of the 19 affected relatives came from families in which probands had reported negative family history of dystonia. Twenty-seven (62%) of the 47 affected individuals had additional forms of dystonia, and 23 had other more generalized movement disorders. In total, 18 (64%) families were multiplex, with 2 to 4 members having dystonia. Autosomal dominant inheritance was suggested in at least 12 families. The findings suggested that there is a genetic component to musician's dystonia, and that phenotypic variability includes focal task-specific dystonia. None of the affected individuals had a mutation in the DYT1 gene.