MAPT and Parkinson disease: The genetic component of PD is also evident from genetic risk factors, derived from candidate gene association studies and genome-wide association studies (GWASs), with SNCA, glucosylceramidase beta (GBA), microtubule-associated protein tau gene (MAPT) and leucine-rich repeat kinase 2 (LRRK2) genes considered as the commonest ones [21,22,23].