Several works showed that BCP MLL-AF4 rearranged leukaemia is characterized by a very low rate of genetic alteration13, 14, 15 and using Sanger sequencing a significant amount of data on the mutational status of RAS genes in infants and paediatric patients with MLL-AF4 leukaemia were previously obtained23, 35, 36, 37. The gene discussed is AFF1; the disease is leukemia.