Recently, many exome sequencing studies have revealed the MLL2 gene as one of the most frequently mutated genes in a variety of human cancers, including follicular lymphoma, diffuse large B-cell lymphoma, renal carcinoma, prostate cancer, bladder carcinoma, gastric carcinoma, breast cancer, lung carcinomas (Dalgliesh et al. 2010; Grasso et al. 2012; Gui et al. 2011; Morin et al. 2011; Pasqualucci et al. 2011; Pleasance et al. 2009; Stephens et al. 2012; Zang et al. 2012), suggesting that MLL2 may play an important role in tumorigenesis in a variety of tumors. The gene discussed is KMT2D; the disease is Familial prostate cancer.