Nature Genet. 41, 1341–1344 (2009)

Transplanted bone marrow cells commonly attack the recipient's cells, even though key proteins on the surface of the donor's and recipient's cells match. To find out what might be the cause of this 'graft-versus-host disease', Steven McCarroll of Harvard Medical School in Boston, Massachusetts, and his colleagues analysed gene deletions in the genomes of 1,345 pairs of patients and immune-matched siblings from whom bone-marrow transplants were made.

They found that the immune attack was more likely to occur when the donor — but not the recipient — had deletions in both copies of the gene UGT2B17. The donor's immune cells seem to respond to the gene's protein as 'foreign' in the recipient.