Mutations in THAP1 underlie a substantial proportion of early-onset primary dystonia in non-DYT1 families. The clinical features that are characteristic of affected individuals who have mutations in THAP1 include limb and cranial muscle involvement, and speech is often affected.

Dystonia is a movement disorder with many presentations and diverse causes. A systematic approach to dystonia helps to ensure that patients with this disorder receive optimum care. This Review begins with a summary of the clinical features of dystonia, followed by a discussion of other disorders to be considered and excluded before assigning the diagnosis of dystonia. Next, we emphasise the importance of classifying dystonia along several dimensions, and we explain how doing so aids in narrowing the differential diagnosis.