3-M syndrome, a primordial growth disorder, is associated with mutations in CUL7 and OBSL1. Exome sequencing now identifies mutations in CCDC8 as a cause of 3-M syndrome. CCDC8 is a widely expressed gene that is transcriptionally associated to CUL7 and OBSL1, and coimmunoprecipitation indicates a physical interaction between CCDC8 and OBSL1 but not CUL7.We propose that CUL7, OBSL1, and CCDC8 are members of a pathway controlling mammalian growth. © 2011 by The American Society of Human Genetics. All rights reserved.