Whispering dysphonia in an Australian family (DYT4): a clinical and genetic reappraisal

Progressive dystonia

Progressive dystonias are a clinically and genetically heterogeneous group of movement disorders. In the primary forms, dystonia is the only sign of the disease, and the cause is either unknown or genetic. In the secondary forms, dystonia is usually only one of several disease manifestations and the cause may be genetic or due to other insults. Monogenic defects have been found to underlie many forms of dystonia syndromes, which are designated DYT1-20. Dystonias with known genes include DYT1 and DYT6 dystonia, presenting as isolated torsion dystonia, as well as DYT5 (dopa-responsive dystonia), DYT11 (myoclonus-dystonia), and DYT12 (rapid-onset dystonia-parkinsonism), where dystonia occurs in conjunction with other types of movement disorders. All of these conditions follow an autosomal dominant mode of inheritance, usually develop in childhood or early adolescence, and show an initially progressive course with stabilization in early adulthood. In secondary dystonias, there are often atypical features and additional neurological signs, such as prominent tongue and perioral involvement, pyramidal signs, ataxia, oculomotor abnormalities, or cognitive disturbances. Acquired brain lesions typically affect the putamen, thalamus, or globus pallidus and cause contralateral hemidystonia. Dystonia can be part of the clinical syndrome in many heredodegenerative disorders, or may be drug-induced or psychogenic.

The genetics of dystonias

Dystonia has been defined as a syndrome of involuntary, sustained muscle contractions affecting one or more sites of the body, frequently causing twisting and repetitive movements or abnormal postures. Dystonia is also a clinical sign that can be the presenting or prominent manifestation of many neurodegenerative and neurometabolic disorders. Etiological categories include primary dystonia, secondary dystonia, heredodegenerative diseases with dystonia, and dystonia plus. Primary dystonia includes syndromes in which dystonia is the sole phenotypic manifestation with the exception that tremor can be present as well. Most primary dystonia begins in adults, and approximately 10% of probands report one or more affected family members. Many cases of childhood- and adolescent-onset dystonia are due to mutations in TOR1A and THAP1. Mutations in THAP1 and CIZ1 have been associated with sporadic and familial adult-onset dystonia. Although significant recent progress had been made in defining the genetic basis for most of the dystonia-plus and heredodegenerative diseases with dystonia, a major gap remains in understanding the genetic etiologies for most cases of adult-onset primary dystonia. Common themes in the cellular biology of dystonia include G1/S cell cycle control, monoaminergic neurotransmission, mitochondrial dysfunction, and the neuronal stress response.