**2. Classification of dystonias**

If defining dystonia is difficult and controversial, classifying the various forms of dystonias is a much more complex task, primarily because the term dystonia can mean not only a disease but also a symptom that can be part of many disorders with a wide range of causes. In an attempt to clarify the term, three "surnames" for dystonia were proposed: "symptom", "movement" and "disorder". A patient may complain of dystonia if, for example, he has a twisted neck. The patient has a dystonia symptom (dystoniaSx). On examination, the signs of dystonia may be confirmed. This patient then has a dystonia movement (dystoniaMov). Finally, dystonia as a disorder (dystoniaDx) requires a clinicopathologic understanding of the etiology of the disease, i.e., whether it is genetic, late-onset, post-traumatic, or has other etiologies [18]. These new definitions led to the replacement of the 1998 dystonia classification [3] by a new one in 2013. The dystonias are now subdivided according to whether they are the result of pathological changes or structural damage, have acquired causes or are hereditary. If there is no clearly defined etiology, the dystonia can be classified as idiopathic familial or idiopathic sporadic [3].

Recent years have seen significant progress being made in our understanding of the genetics of dystonias as new loci and genes have been identified. For generalized dystonias, the genetic mechanisms are better understood, while for focal dystonias, the genes and genetic suscepti‐ bility to the disorder are not yet well identified. Hereditary dystonias (dystoniaDx) are clinically and genetically heterogeneous. The known genetic forms include all monogenic inheritance patterns (autosomal recessive, autosomal dominant, and X-linked). Table 1 shows the heredi‐ tary dystonias grouped according to their similarities. They are divided according to their clinical features (axis I) and etiology (axis II) in line with the new 2013 classification.
