Nat. Genet. 45, 639–647 (2013); published online 21 April 2013; corrected after print 28 June 2013

In the version of this article initially published, the label “– Tub” in Figure 3d was placed incorrectly. The label should appear adjacent to the lower bracketed panels rather than adjacent to the bottom portion of the upper bracketed panels. The error has been corrected in the HTML and PDF versions of the article.