The two most consistently identified susceptibility genes for sporadic PD are the α-synuclein (SNCA) and microtubule-associated protein tau (MAPT) genes [10, 11] which play independent, but not joint, effects on the risk of developing PD [12, 13], although there are significant differences in the variants associated with PD between Asian and Caucasian populations [14]. This evidence concerns the gene SNCA and Parkinson disease.