MAPT and Alzheimer disease: Trimethylamine N-oxide (TMAO), a small molecule produced by the metaorganismal metabolism of dietary choline, is also higher in individuals with MCI and AD dementia compared to cognitively-unimpaired individuals, and elevated CSF TMAO is associated with biomarkers of AD pathology (phosphorylated tau and phosphorylated tau/Aβ42) and neuronal degeneration (total tau and neurofilament light chain protein) [41].