CSF total tau (T‐tau) is a well‐studied biomarker, which is increased in neuronal degeneration (Blennow et al, 2006) and in AD patients already in early clinical stages (Mattsson et al, 2009; Albert et al, 2011; McKhann et al, 2011; Sperling et al, 2011; Dubois et al, 2014). The gene discussed is MAPT; the disease is Alzheimer disease.