MAPT and Alzheimer disease: However, assessments of Aβ and pathological tau accumulation in the brain using positron emission tomography (PET) scan, the gold standard for ante mortem detection of AD pathology,4 are expensive and not easily accessible, particularly in rural areas and underdeveloped countries, whereas cerebrospinal fluid (CSF) sampling suffers the same drawbacks of PET scan and in addition faces resistance from patients and research participants due to its invasive nature and cultural considerations.