Dystonia is characterized by sustained or intermittent muscle contractions that produce abnormal, often repetitive, postures and movements. Symptoms of dystonia can begin early in childhood until late adulthood, affecting one part of the body (focal), several (multifocal, segmental), or many (generalized). Usually, this last group of generalized dystonias usually consist of progressive and disabling disorders that begin in adolescence, with a known genetic basis. The group of primary focal dystonias almost always occur in adults and usually involve the neck, face or arms, with a smaller number of known genes, although up to 25% usually have a positive family history (Steeves et al., 2012). ). It should be noted that dystonias are diseases with great phenotypic and genotypic heterogeneity, in many cases with incomplete penetrance even within the same family (Albanese et al., 2013).
A prevalence of about 16:100,000 individuals is estimated (Steeves et al., 2012).
Although there are numerous risk factors described through association studies, the diagnostic-genetic approach is aimed at being able to make diagnoses of clinical applicability for the patient.
For this, four phenotypic groups have been established:
- Isolated dystonia (primary, focal or generalized, as main symptom): basic panel of 8 genes, with particular relevance of TOR1A (DYT1), THAP1 (DYT6) and GNAL (DYT25, adult craniocervical dystonia).
- Myoclonic dystonia: specific panel of 2 genes, including SGCE or DYT11, whose yield is up to 50% in familial cases, and the most recently described KCTD17.
- Dystonia–parkinsonism: includes, among others, genes related to dopa-sensitive dystonia or Segawa disease.
- Paroxysmal dystonia in combination with another dyskinesia, which includes the genes PNKD, PRRT2, SLC2A1 and ECHS1 .
All these phenotypes are collected in a general panel for the study of dystonia, indicated for a more exhaustive etiological approach and in complex cases.