GCH1 and dystonia 5: Suzuki and colleagues74) have found substantial loss of GTPCH protein in phytohemagglutinin-stimulated mononuclear blood cells from GTPCH-deficient DRD patients (with a frameshift or missense GCH1 mutation) and have indicated that reduction of the amount of GTPCH protein, which is independent of the GCH1 mutation type, contributes to the mechanism of dominant inheritance.