Clinical heterogeneity of dopa-responsive dystonia: PET observations

Parkinsonism without dystonia has been reported in several older members of families with DRD. This raises the question whether such patients represent a variant in the clinical picture of DRD, or a separate disease, IP. We employed 6-FD PET to study the nigrostriatal dopaminergic function in a woman with typical DRD and two of her relatives with late-onset parkinsonism. These two had an excellent and prolonged therapeutic response to small doses of L-DOPA, without complications. We found that the dystonic patient and the women with "benign" parkinsonism had normal striatal 6-FD uptake. In conjunction with other clinical evidence, our PET study indicates that the biochemical lesion in these members may be "proximal" to dopa decarboxylase, as is suggested in DRD patients. We conclude that the adult-onset parkinsonism in DRD families is due to the same pathophysiological mechanism as the childhood-onset dystonia in the disease. DRD may display substantial clinical heterogeneity depending on the age of onset.