Nat Genet. 47, 555–559 (2015); published online 6 April 2015; corrected after print 14 August 2015
In the version of this article initially published, the authors neglected to acknowledge one of the funding sources for their study. The acknowledgements should have recognized support from Chinese NSF grant 91231120 in addition to the other funding sources listed. The error has been corrected in the HTML and PDF versions of the article.