Tau is a marker of injury to neuronal axons that is predominantly expressed by neurons and localized within axons where it stabilizes microtubule networks.20 In CM, as in various neurologic disorders including TBI and Alzheimer disease, elevated cerebrospinal fluid (CSF) levels of tau have been associated with persistent NCI.4,21,22 The use of tau as a biomarker of neurologic injury was previously restricted to populations where CSF is accessible, due to its low abundance in blood and lack of sensitive detection tools. Here, MAPT is linked to early-onset autosomal dominant Alzheimer disease.