MAPT and familial Alzheimer disease: The U1 snRNA, that serves as the backbone of the U1 snRNP complex, but not U2, U4, U5, and U6 snRNA, is enriched in familial Alzheimer disease (AD), which is characterized by β-amyloid aggregates and MAPT/tau protein hyperphosphorylation, as well as mitochondrial dysfunction and defective mitophagy (reviewed in12).