MAPT and Alzheimer disease: Moreover, the CSF Aβ42 biomarker, most commonly combined with total tau protein as a ratio, can identify AD pathology long before dementia by distinguishing CH people with normal versus abnormal CSF biomarkers of AD: CH participants with normal Aβ42/Tau (CH-NAT) versus CH participants with abnormal or pathological Aβ42/Tau (CH-PAT; Fagan et al., 2007).