We conducted a large case control study of MAPT variants previously shown to be associated with neurodegenerative disorders (Goris et al., 2007; Skipper et al., 2004; Tobin et al., 2008; Vandrovcova et al., 2009); based on the hypothesis that common variation in the MAPT gene is a major factor responsible for the incomplete penetrance in LHON. The gene discussed is MAPT; the disease is Leber hereditary optic neuropathy.