Clinical features and classification of the human dystonias

Dystonia is characterized by sustained muscle contractions causing twisting and repetitive movements and postures, which are often precipitated by action. Dystonia may be limited to a single muscle group, such as spasm of a vocal cord adductor, or it may affect entire body regions, as in generalized dystonia involving the legs, the trunk, and the arms. Dystonia may be due to a myriad of genetic etiologies or may be secondary to various toxic causes. However, Human Genome Organization/ Genome Database (HUGO/GDB) designation lists a very diverse group of dystonias in chronologic order by year of discovery and does not account for the majority of dystonias; therefore, this chapter focuses on the proposed clinical classification and discusses where the HUGO/GDB designations are integrated into this schema. As a framework for understanding animal models of dystonia, the chapter briefly discusses the epidemiology and pathology of the human dystonias and then more thoroughly review the clinical features of the major forms of primary dystonias and dystonia-plus syndromes. Greater understanding of and better treatments for dystonia is possible through the study of relevant animal models and the use of additional biochemical, neuropyschiatric, molecular genetic, and neuroimaging tools.