Interestingly, murine models so far have achieved a transient production of KMT2A‐AFF1 proteins but failed to express the phenotype observed in humans.27, 28, 29 Only recently, the development of such models is becoming increasingly closer to clinical phenotypes.30, 31 Therefore, in vitro models have been at the forefront of research into KMT2A‐leukaemia. The gene discussed is AFF1; the disease is leukemia.