In bone marrow transplantation of hematopoietic stem cells (HSCT), slight variations and mismatch of the histocompatability leucocyte antigens (HLA) can lead to a serious and life-threatening complications known as graft-versus-host disease (GVHD/the donor's immune cells attack the tissues of the host). In the November 22nd online edition of Nature Genetics, S. A. McCarroll et al. from Massachusetts General Hospital reported in a letter that their study results show that homozygous deletion of the gene, UGT2B17, in the donor's cells increased the risk of GVHD in the recipient. The study was based on analyzing common gene deletions in three HSCT cohorts of 1,345 HLA-identical sibling donor-recipient pairs). Mismatching due to deletion of UGT2B17 had a greater risk of acute GVHD (odds ratio=2.5 with a 95% confidence interval of 1.4-4.6). The authors concluded that human structural variation in which proteins other than HLA are targeted by the immune system as another "potential mechanism in diseases of alloimmunity."