LETM1 and Wolf-Hirschhorn syndrome: A region spanning ~165 kilobases in chromosome 4 represents the region deleted in WHS patients, comprising LETM1, MSX1, a homeobox gene involved in the development of mouth and teeth structures, and WHSC1, a histone H3 lysine methyltransferase that interacts with β-catenin [65,66,67,101].