The Dystonic Brain: Electrophysiological Investigation of Carriers of the DYT1 Gene Mutation

A mutation in the DYT1 gene on chromosome 9q34 is the commonest cause of young-onset primary dystonia. The penetrance of clinical symptoms is low (only 30-40% of gene carriers manifest dystonia), and occurs in an agedependent fashion. Mutation carriers who pass their mid-twenties without developing symptoms almost invariably stay symptom free for life. DYT1 mutation carriers therefore provide a unique model with which to study brain function in primary dystonia, and factors that may protect against development of clinical symptoms in those who are genetically susceptible. This thesis describes the use of electrophysiological techniques to determine 1) if manifesting DYT1 carriers have similar deficits in motor function to nongenetic primary dystonia, and 2) what are the consequences of the DYT1 mutation for motor system physiology in non-manifesting carriers. We found abnormalities of inhibitory motor circuits at cortical and spinal cord levels in manifesting DYT1 subjects. Surprisingly, we found cortical motor abnormalities of a similar nature and severity in non-manifesting DYT1 carriers, despite their lack of symptoms. We subsequently demonstrated abnormal reciprocal inhibition in manifesting DYT1 subjects was partially normalised by 1Hz repetitive transcranial magnetic stimulation (rTMS), but that this same stimulus had no effect on