Gain of function mutations in HAT enzymes have been identified in different types of cancer and could in turn lead to increased histone acetylation.62 Furthermore, hyperacetylation of H4 is partly caused by loss of function of HDAC1 in chronic myeloid leukaemia.63 Thus, H4 hyperacetylation may be a result and not a cause of cancer development. This evidence concerns the gene HDAC1 and chronic myelogenous leukemia, BCR-ABL1 positive.