MAPT and Parkinson disease: In addition to the familial PD-linked genes, several genomic loci have been designated in linkage studies as either being linked or influencing the age of onset of PD, such as microtubule-associated protein tau (MAPT) and ubiquitin carboxyl-terminal esterase L1 (UCHL1) [for review of candidate genes studied today, see (Rosner et al. 2008; Farrer 2006; Wider et al. 2010)].