To the Editor We read with great interest the article by Kumar and colleagues1 published in JAMA Neurology. They screened 318 patients with different types of dystonia, mainly sporadic, from Germany, Serbia, and Japan for mutations in all 12 exons of GNAL and found 2 putative mutations (c.637G>A and c.1057G>A) in 2 sporadic cases with craniocervical dystonia and cervical dystonia, respectively. The prevalence estimate of GNAL cases according to their figure is 0.62%, which is much lower than originally reported.2 The initial discovery report by Fuchs et al2 reported GNAL mutations in 6 of 39 families screened (approximately 15%). However, in the subsequent study by Vemula et al,3 only 3 GNAL mutations were detected in 760 individuals with familial or sporadic primary dystonia (<0.5%). Furthermore, a number of groups have subsequently screened different cohorts of patients with dystonia for GNAL mutations, yielding conflicting prevalence estimates (Table).
Erro R, Bhatia KP, Hardy J. GNAL Mutations and Dystonia. JAMA Neurol. 2014;71(8):1052-1053. doi:10.1001/jamaneurol.2014.1506