AFF1 and acute lymphoblastic leukemia: However, up to 80% of infant ALL patients younger than 1 year and most patients with ALL linked to treatment with DNA topoisomerase II inhibitors carry such rearrangements.[3] So far, MLL has been found to be involved in >100 different translocations in ALL, and >60 translocation partner genes have been molecularly characterized.[4]AFF1 (also known as AF4) is the most common partner gene, and MLL-AFF1 fusion occurs in 46% of infant acute ALL patients.