Nature Genetics 39, 933–934 (2007); published online 27 July 2007; corrected after print 30 October 2007

In the version of this article initially published, the second author (Jens Hansen) should have been listed as an equal contributor with the first author. The last two authors (Harald von Melchner and Patricia Ruiz Noppinger) should have been listed as corresponding authors. The error has been corrected in the HTML and PDF versions of the article.