Over 79 different fusion partners of MLL1 have been identified and molecularly characterized; the most common fusion partners are AF4 (AFF1), AF9 (MLLT3), AF10 (MLLT10) and ENL (MLLT1) corresponding to t(4;11), t(9;11), t(10;11) and t(11;19) translocations respectively and together accounting for almost 80% of all MLL-r leukemias [12]. The gene discussed is AFF1; the disease is leukemia.