The dystonias comprise a heterogeneous group of movement disorders. In contrast to the frequent sporadic forms, a variety of rare familial forms are caused by genetic mutations with mendelian inheritance. In recent years, significant progress has been made with regard to the identification of genes causing dystonia, and to the molecular pathophysiology underlying dystonic symptoms. Currently, 18 gene loci have been described causing primary dystonia, dystonia-plus syndromes or paroxysmal dystonia. The most frequent form of inherited dystonia, according to current knowledge, is early-onset generalized DYT1 dystonia, caused by a deletion of three basepairs, GAG, in the DYT1 (TOR1A) gene. It is thought that the protein encoded by this gene, torsinA, participates in association of the endoplasmatic reticulum and the nuclear envelope with the cytoskeleton and hereby might influence the reaction of cells to various stresses and/or the development of specific neuronal populations involved in movement control in the brain. Other genes which have only recently been identified include: THAP1, causing adolescent-onset primary dystonia of mixed type (DYT6); ATP1A3, responsible for Rapid-Onset Dystonia-Parkinsonism (RDP, DYT12); PRKRA, causing young-onset dystonia-parkinsonism (DYT16); and SLC2A1, causing paroxysmal exertion-induced dystonia with haemolytic anemia (DYT18). Further, five other loci for primary dystonia (DYT2, DYT4, DYT7, DYT13 and DYT17) have been identified, for which the causative genes remain to be discovered.