KMT2B and Alzheimer disease: Also, PFC neurons depend critically on lysine methyltransferase 2A (KMT2A, also known as MLL1) and mildly on lysine methyltransferase 2B (KMT2B, also known as MLL2) to maintain H3K4me3 levels at a subset of genes with an essential role in cognition and emotion, for example, at the ARC immediate early gene, which is an important mediator of synaptic plasticity and an AD susceptibility gene 280, 281.