Importantly, levels of cerebrospinal fluid (CSF) AD biomarkers, including beta-amyloid 1–42 (Aβ42), total tau (t-Tau), and tau phosphorylated at threonine 181 (p-Tau181), remain relatively stable after disease onset, and do not differentiate between mild cognitive impairment due to AD (MCI) and mild AD dementia [4, 5]. The gene discussed is MAPT; the disease is Alzheimer disease.