H6PD and Parkinson disease: The potential of NADPH to prevent nigral neurodegeneration in PD was demonstrated in pioneering experiments on transgenic expression of the G6PDH in dopaminergic neurons of the substantia nigra; such an increase in activity led to neuroprotection in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD [43].