Nat. Genet. 40, 789–793 (2008); published online 25 May 2008; corrected after print 26 June 2008

In the version of this article initially published, Figure 3a–d and Supplementary Figure 2a–c show 16-OH PGE2, not 15-OH PGE2. The errors have been corrected in the HTML and PDF versions of the article.