AFF1 and leukemia: Although MLL fuses with a variety of partners, most MLL fusion-mediated leukemia cases are caused by the fusions with the AF4 family (e.g., AF4 also known as AFF1, AF5Q31 also known as AFF4) and ENL family (e.g., ENL also known as MLLT1, AF9 also known as MLLT3) (Meyer et al., 2018).