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Tracy Hampton, PhD

JAMA. 2007;297:2339.

	Since this article does not have an abstract, we have provided the first 130 words of the full text and any section headings.

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.

The gene encoding SMCX is frequently mutated in X-linked mental retardation, in which defects in genes on the X chromosome are inherited. Therefore, the investigators hypothesize that mutations in SMCX may contribute to disease by impairing regulation of neuronal genes.