Cervical Dystonia

Causes/Genetics

In most cases, the exact cause of CD is usually not known. The condition appears sporadically, in the absence of a documented family history of the disease. In about 10% to 15% of cases, more than one family member may be affected. Several families have been described with autosomal dominant, adult-onset, primary dystonia that is focal in distribution, affecting the neck region. This form of the condition has been called "familial torticollis." In one German kindred, the autosomal dominant disorder was mapped to chromosome 18p. This genetic location or locus has been designated as DYT7. However, other kindreds with familial torticollis have been excluded from the DYT7 as well as the DYT1 regions and the responsible gene location has not yet been identified.

In most patients, the role of heredity in primary adult-onset focal/segmental dystonia remains unknown. Some researchers suggest that heredity may be a factor in the development of these dystonias, based upon several findings, such as the following:

• In addition to the kindreds discussed above, familial cases of primary adult-onset focal dystonia have been reported, including cervical dystonia.
• In one study, 25 of 40 non-Jewish individuals with a focal dystonia such as cervical dystonia or writer's cramp had relatives with symptoms of dystonia.
• According to multiple large studies of primary adult-onset focal dystonia, 2% to 15% of patients have had relatives with signs of focal or segmental (but not generalized) dystonia.

Based upon these and other findings, some researchers suggest that primary adult-onset focal dystonias may commonly be transmitted as an autosomal dominant trait with reduced penetrance and variable expressivity. In addition, some investigators speculate that adult-onset primary focal dystonias may represent a localized manifestation of primary generalized dystonia, with the final anatomical distribution reflecting patient age and specific site of onset. Possible support for this theory includes the fact that primary generalized dystonia often begins as a focal dystonia. In addition, primary focal and generalized dystonias are both characterized by effective sensory tricks and both respond similarly to certain medications.

Dystonia that begins in the neck or cranial region rarely results from mutations of the DYT1 gene, indicating that most focal dystonias that do not begin in a limb are probably distinct from primary generalized dystonia. Therefore, whether primary focal and generalized dystonias may be variations of the same disorders or are truly distinct disease entities remains unclear.

Some studies also suggest that focal dystonia may be precipitated by trauma or overuse of the affected region of the body. For example, some researchers theorize that prior trauma may play some role in triggering disease onset in patients who carry a mutated DYT1 gene for DYT1 dystonia. In addition, several studies have suggested a possible association of focal dystonias with prior peripheral trauma. For example, researchers have reported that trauma occurred three to six months prior to symptom onset in approximately 5% to 12% of patients with cervical dystonia.

In some cases, the relationship between trauma and the onset of dystonia is clear when dystonia follows brain injury or severe peripheral trauma. However, in many patients, the relationship is less clear and trauma alone probably would not be sufficient for the development of dystonia. Rather, some research suggests that trauma may play some role in triggering dystonia in those with previously, very mild, undetectable cases-or in patients with an existing, potentially genetic, susceptibility to the disorder. Further research is necessary to determine the various underlying genetic, environmental, or other underlying mechanisms that may play a role in causing the focal dystonias, including cervical dystonia.