Cerebrospinal fluid sampling is used to exclude inflammatory, infective, and malignancy related causes of dementia and is typically recommended in individuals with rapid cognitive decline, unusual or neurological presentations, or cognitive impairment at less than 55 years of age.28 More recently there has been a focus on developing cerebrospinal fluid based markers, such as β amyloid and tau, for changes in Alzheimer’s disease that can predate the onset of the dementia, the so called prodromal phase of Alzheimer’s disease. Here, MAPT is linked to early-onset autosomal dominant Alzheimer disease.