Mutations in DYT1 -: Extension of the phenotypic and mutational spectrum

Background: Most cases of early-onset primary torsion dystonia (PTD) are caused by the same three-base pair (bp) (GAG) deletion in the DYT1 gene. Exon rearrangements are a common mutation type in other genes and have not yet been tested for in DYT1. Several lines of evidence suggest a relationship of the DYT1 gene with Parkinson disease (PD). Objective: To investigate the frequency and type of DYT1 mutations and explore the associated phenotypes in a mixed movement disorders patient cohort and in controls. Methods: The authors screened 197 patients with dystonia (generalized: n=5; focal/segmental: n=126; myoclonus-dystonia: n=34; neuroleptic-induced: n=32), 435 with PD, and 42 with various other movement disorders, along with 812 healthy controls, for small deletions in exon 5 of DYT1 and tested for exon rearrangements by quantitative, duplex PCR in 51 GAG deletion-negative dystonia cases. Results: The GAG deletion was detected in five patients: three with early-onset PTD, one with generalized jerky or clonic dystonia, and one with generalized dystonia and additional features (developmental delay, pyramidal syndrome). A novel out-of-frame four-bp deletion (934_937delAGAG) in exon 5 of the DYT1 gene was found in a putatively healthy blood donor. No exon rearrangements were identified in DYT1. Conclusions: In this mixed patient sample, the GAG deletion was rare and in two out of five cases associated with an unusual phenotype. In addition, a novel DYT1 truncating mutation of unknown clinical relevance was found in a putatively unaffected individual. DYT1 exon rearrangements, however, do not seem to be associated with PTD.