PADI4 and leukemia: Histone citrullination is antagonistic to histone arginine methylation (Cuthbert et al., 2004; Wang et al., 2004), a modification that has established roles in the regulation of haematopoiesis (Kolodziej et al., 2014; Greenblatt et al., 2016) and PADI4 was previously shown to influence gene expression by counteracting arginine methylation in leukaemia cells (Kolodziej et al., 2014).