Mutations in THAP1 (DYT6) and generalised dystonia with prominent spasmodic dysphonia: a genetic screening study

Background: DYT6 is a primary, early-onset torsion dystonia; however, unlike in DYT1 dystonia, the symptoms of DYT6 dystonia frequently involve the craniocervical region. Recently, two mutations in THAP1, the gene that encodes THAP (thanatos-associated protein) domain-containing apoptosis-associated protein 1 (THAP1), have been identified as a cause of DYT6 dystonia. Methods: We screened THAP1 by sequence analysis and quantitative real-time polymerase chain reaction (PCR) in 160 white patients of European ancestry who had dystonia with an early age at onset (n=64), generalised dystonia (n=35), a positive family history of dystonia (n=56), or facial or laryngeal dystonia. Another 160 patients with dystonia were screened for reported and novel variants in THAP1. 280 neurologically healthy controls were screened for the newly identified and previously reported changes in THAP1 and these and an additional 75 controls were screened for a rare non-coding mutation. Findings: We identified two mutations in THAP1 (388_389delTC and 474delA), respectively, in two (1%) German patients from the 160 patients with dystonia. Both mutation carriers had laryngeal dystonia that started in childhood and both went on to develop generalised dystonia. Thus, two of three patients with early-onset generalised dystonia with orobulbar involvement had mutations in THAP1. One of the identified patients with DYT6 dystonia had two family members with subtle motor signs who also carried the same mutation. A rare substitution in the 5′untranslated region (-236_235GA→TT) was found in 20 of 320 patients and in seven of 355 controls (p=0·0054). Interpretation: Although mutations in THAP1 might have only a minor role in patients with different, but mainly focal, forms of dystonia, they do seem to be associated with early-onset generalised dystonia with spasmodic dysphonia. This combination of symptoms might be a characteristic feature of DYT6 dystonia and could be useful in the differential diagnosis of DYT1, DYT4, DYT12, and DYT17 dystonia. In addition to the identified mutations, a rare non-coding substitution in THAP1 might increase the risk of dystonia. Funding: Deutsche Forschungsgemeinschaft; Volkswagen Foundation; Dystonia Medical Research Foundation; University of Lübeck.