PRDM9 and Wolf-Hirschhorn syndrome: Interestingly, another histone methyltransferase, WHSC1 (also known as MMSET/NSD2), was recurrently mutated in T-ALL and, although in a small number of patients, mutually exclusive within MLL2. WHSC1, associated with the so called Wolf-Hirschhorn syndrome[51], was only very recently found to be mutated in pediatric ALL, particularly in t(12;21) ETV6-RUNX1 ALL[45,46], as well as in mantle cell lymphoma[42].