Given that the majority of prior studies used primary or immortalized MLL1F cell lines representing late stage tumorigenesis, our investigation explored the consequences of a homozygous point mutation causing the loss of histone methyltransferase activity in MLL1 within human-induced pluripotent stem (iPS) cells, an attractive model for understanding mechanisms of cancer initiation (51). The gene discussed is PRDM9; the disease is cancer.