Dopa-responsive dystonia: a syndrome of selective nigrostriatal dopaminergic deficiency.

Dopa-responsive dystonia (DRD) is no longer a rare oddity. For the clinician, DRD poses a diagnostic challenge as its clinical presentation can be quite diverse. Marked and sustained response to L-dopa is the most crucial and absolute hallmark in confirming a diagnosis. Absence of degenerative nigral cell loss underlies the remarkable L-dopa response. The broadening spectrum of the clinical presentations, progress in molecular genetics with evidence of incomplete penetrance and phenotypic variability, biochemistry, utility of nuclear imaging in differential diagnosis, and treatment are discussed. I propose the concept of DRD as a syndrome, defined as selective nigrostriatal dopamine deficiency caused by genetic defects in dopamine synthesis without degenerative cell loss. I further propose the term DRD-plus, defined as inherited metabolic disorders which have symptomatic features of DRD, and those features not seen in DRD as well.