GCH1 and Dystonia: Nevertheless it has been repeatedly reported, through analysis of brain tissue (Furukawa et al., 2002), CSF (Takahashi et al., 1994) and urine (Leuzzi et al., 2013), that even completely asymptomatic carriers of GCH1 mutations have abnormal metabolism of biopterins and dopamine, although to a lesser extent than DOPA-responsive dystonia cases.