Now regarding specific genetic variations linking drug abuse and PD, although PD has been described as a prototypical sporadic disease, advancement in molecular genetic studies has revealed this neurodegenerative disorder as a genetic disorder [44], with the traditional model of PD being SNCA-centric, although the microtubule-associated protein tau (MAPT) gene locus has come out to be also a risk factor for PD [45]. Here, MAPT is linked to Parkinson disease.