A number of studies of concordant leukemia have provided evidence to support the sharing of a leukemia initiating clone from one twin to the other (reviewed in 37) An identical DNA rearrangement to the immunoglobulin heavy chain was seen to be shared by B-cell lineage ALL cells from a pair of infant Siamese twin boys who were separated 42 days after birth and both diagnosed with ALL 7 months later. Here, SLC3A2 is linked to acute lymphoblastic leukemia.