Researchers at Brigham and Women's Hospital and Harvard Medical School, in Boston, and the University of Florida College of Medicine, in Gainesville, have recently deciphered how a protein called SMCX previously implicated in mental retardation may contribute to the development of the disease (Tahiliani M et al. Nature. doi:10.1038/nature05823 [published online ahead of print April 29, 2007]).
SMCX modifies histones that package DNA into chromatin to form chromosomes. Specifically, the protein removes trimethyl groups from a particular histone (H3) and represses transcription of certain neuronal genes.
Hampton T. Mental Retardation Clue. JAMA. 2007;297(21):2339. doi:10.1001/jama.297.21.2339-c