SPR and dopa-responsive dystonia: To date, three genes have been convincingly shown to cause DOPA-responsive dystonia: GCH1 (GTP cyclohydrolase 1), TH (tyrosine hydroxylase) and SPR (sepiapterin reductase) (Ichinose et al., 1994; Brautigam et al., 1998; Bonafe et al., 2001).