Interestingly, the protectiveactivity of GDNF in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model ofparkinsonism requires the presence of TGF-β [27], suggesting thatstrategies aimed at enhancing the endogenous production of both GDNF andTGF-β may be particularly successful in slowing the progression ofParkinson's disease. This evidence concerns the gene GDNF and glycogen storage disease VI.