Nat. Genet. 45, 314–318 (2013); doi:10.1038/ng.2554; published online 10 February 2013; corrected after print 9 May 2013

In the version of this article initially published, the affiliations of Daniel W.H. Ho were incorrect, and the spelling of Sarayut Janmahasatian in the author list was incorrect. The errors have been corrected in the HTML and PDF versions of this article.