MAPT and Parkinson disease: MAPT encodes 6 isoforms of tau, a microtubule-associated protein largely seen in the cytoplasm and axons (Wang and Mandelkow 2016); in addition to being a key player in AD pathogenesis, variants at the MAPT locus represent the second most commonly associated risk factor for PD by GWAS analysis (after changes at the SNCA locus) (Edwards et al. 2010).