We thank Melih Acar, Hillary Andrews, Vafa Bayat, Lee Grimes, Haluk Lacin, Clayton Morrison, Elaine Seto, Hiroshi Tsuda, Koen Venken, and Huda Zoghbi for comments on the manuscript and Cheng-Ting Chien and Lee Grimes for sharing unpublished data.
H.J.-N. is supported by NIH Medical Genetics Research Fellowship Program grant T32-GMO7526. This work was supported by a grant from NASA. H.J.-N. is an associate and H.J.B. is an investigator of the Howard Hughes Medical Institute.