Genetics of primary torsion dystonia.

Advances in the genetics of dystonia have further elucidated the pathophysiology of this clinically and etiologically heterogeneous group of movement disorders. Currently, 20 monogenic forms of dystonia, designated by the acronym DYT, are grouped as 1) pure dystonias, 2) dystonia-plus syndromes, and 3) paroxysmal dystonias/dyskinesias. We summarize recently discovered genes and loci, including the 1) detection of two primary dystonia genes (DYT6, DYT16), 2) identification of the DYT17 locus, 3) association of a dystonia/dyskinesia phenotype with a gene previously linked to GLUT1 (glucose transporter of the blood-brain barrier) deficiency syndrome (DYT18), 4) designation of paroxysmal kinesigenic and nonkinesigenic dyskinesia as DYT19 and DYT20, and 5) redefinition of DYT14 as DYT5. Further, we review current knowledge regarding genetic modifiers and susceptibility factors. Because recognizing and diagnosing monogenic dystonias have important implications for patients and their families with regard to counseling, prognosis, and treatment, we highlight clinical "red flags" of individual subtypes and review guidelines for genetic testing.