THAP1

Primary torsion dystonia (PTD) is characterized by sustained muscle contractions that cause twisting and repetitive movements, where dystonia is the only or predominant clinical feature. The clinical spectrum associated with PTD is remarkably broad. Symptoms may begin at any age and severity ranges from involvement of a single muscle to generalized contractions of the limb, axial, and cranial muscles. When PTD begins in childhood, it often progresses to involve multiple body regions. When PTD begins in adult years, dystonia tends to remain localized with a focal or segmental distribution. The prevalence of PTD has been estimated between 330 per million to 152 per million, the great majority being focal.¹

Seven genes have been mapped for primary dystonia including DYT1, 2, 4, 6, 7, 13, and 17²; however, only 2 of these genes have been identified: TOR1A (DYT1)³ and the recently described THAP1 (DYT6) gene.⁴ A 3-bp (GAG) deletion in the coding region of the TOR1A gene is a major cause of childhood onset, generalized dystonia that usually begins in a limb.³ DYT6 dystonia was described in three Amish-Mennonite families who share a disease haplotype that could be traced to a …