Examples of highly reproducible biomarkers that to some degree are used in clinical practice for diagnosis of neurodegenerative diseases include CSF Aβ42, the Aβ42/40 ratio, total-tau (T-tau) and phosphorylated tau (P-tau) for AD diagnosis4, and real-time quaking-induced conversion (RT-QuIC) assays on CSF for CJD5–7. The gene discussed is MAPT; the disease is Alzheimer disease.