Genetic haplotypes at five marker loci that are closely linked to the DYT1 gene on chromosome 9q were determined in 10 Ashkenazi Jewish patients with focal hand dystonia (eight with musician's cramp, two with writer's cramp).
To determine the frequency of this mutation in a larger series of patients, we examined 44 index patients with sporadic or familial (seven patients) writer's cramp for the presence of the DYT1 GAG deletion, including eight patients with segmental dystonia involving at least one upper limb.
Analysis of 83 published series including 5,057 patients indicated significant differences in the mean age at onset of five phenotypes of PTD (mean age at onset; 95% CI): DYT1 dystonia (11.3 years; 10.3 to 12.2), writer's cramp (38.4; 36.9 to 39.9), CD (40.8; 40.3 to 41.3), spasmodic dysphonia (43.0; 42.2 to 43.9), and blepharospasm-oromandibular dystonia (55.7; 55.1 to 56.4).
Hyperekplexia phenotype of glycine receptor alpha1 subunit mutant mice identifies Zn(2+) as an essential endogenous modulator of glycinergic neurotransmission.