Nat. Med.; 10.1038/nm.3646; corrected online 31 October 2014

In the version of this article initially published online, affiliation 12 was missing for Roland Rad, Roland M. Schmid and Dieter Saur. The list should have read: “Roland Rad1,5,12,13, Roland M Schmid1,12,13 & Dieter Saur1,12,13.” The error has been corrected for the print, PDF and HTML versions of this article.