Missense mutants inactivate guanosine triphosphate cyclohydrolase I in hereditary progressive dystonia

Hereditary progressive dystonia (HPD) with marked diurnal fluctuation is ca used by mutant guanosine triphosphate (GTP) cyclohydrolase I (GCH). The cli nical presentation of dominant HPD varies considerably. We proposed the hyp othesis that a relative increase of mutant GCH capable of inhibiting normal GCH is responsible for heterogeneous phenotypic manifestations. In a Japan ese family with a novel G90V mutation, an affected heterozygote had a highe r mutant/normal mRNA ratio than an unaffected heterozygote. Co-expression a nalysis showed that mutant enzyme (GCH-G90V) inactivated the normal enzyme in the COS cells. Similarly, GCH-G203R showed the dominant negative effects . These results supported our proposed hypothesis. (C) 2000 Elsevier Scienc e B.V. All lights reserved.