Nonmotor Symptoms in Dopa-Responsive Dystonia

Background: Dopa-responsive dystonia (DRD) is a rare inherited dystonia, caused by an autosomal dominantly inherited defect in the gene GCH1 that encodes guanosine triphosphate cyclohydrolase 1. It catalyzes the first and rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin, which is the essential co-factor for aromatic amino acid hydroxylases. Mutation results in the typical scenario of a young-onset lower-limb dystonia with diurnal fluctuations, concurrent or subsequent development of parkinsonism and excellent response to levodopa. Given the myriad functions of tetrahydrobiopterin, it is reasonable that other systems, apart from motor, would also be impaired. So far, non-motor symptoms have been overlooked and very few and often contrasting data are currently available on the matter. Methods: Here by searching the Medline database for publications between 1971 to March 2015, we render an in-depth analysis of all published data on non-motor symptoms in DRD. Results: Depression and subtle sleep quality impairment have been reported among the different cohorts, while current data do not support any alterations of the cardiologic and autonomic systems. However, there is debate about the occurrence of sleep-related movement disorders and cognitive function. Non-motor symptoms are instead frequently reported among the clinical spectrum of other neurotransmitter disorders which may sometimes mimic DRD phenotype, ie, DRD plus diseases. Conclusions: Further studies in larger and treatment-naive cohorts are needed to better elucidate the extend of non-motor symptoms in DRD and also to consider treatment for these.