Dopa-responsive dystonia: recent advances and remaining issues to be addressed.

It is evident from this review that there is much that we know and much that we still do not know about DRD. In terms of diagnosis and clinical management, there is general agreement that patients with childhood-onset dystonic symptoms of unknown etiology should be treated initially with levodopa with the later addition, if necessary, of other medications (for example, BH4, 5-hydroxytryptophan). Although the results of molecular genetic and CSF studies are, at this time, unlikely to significantly alter clinical management of the patient, these analyses could be useful in providing information on prognosis (that is, DRD versus progressive neurodegenerative disorders or more severe metabolic disorders). It is also clear that notwithstanding the discovery of GCH1 and hTH mutations responsible for DRD, there remain many important unresolved issues regarding this disorder, including questions of female predominance, phenotypic heterogeneity, and presence of childhood-onset dystonia versus the expected parkinsonism resulting from a striatal DA deficit. We are confident that answers to these interesting questions on DRD will, in addition to providing clarification of the mechanisms of this disorder, provide exciting information relating to the pathogenesis of other types of dystonia as well as PD and to long-standing issues regarding a role of DA and serotonin in normal human brain development.