About 20 years ago, scientists discovered the gene that causes Huntington’s disease, a fatal neurodegenerative disorder that affects about 30,000 Americans. The mutant form of the gene has many extra DNA repeats in the middle of the gene, but scientists have yet to determine how that extra length produces Huntington’s symptoms. In a new step toward answering that question, MIT biological engineers have found that the protein encoded by this mutant gene alters patterns of chemical modifications of DNA. This type of modification, known as methylation, controls whether genes are turned on or off at any given time. The mutant form of this protein, dubbed “huntingtin,” appears to specifically target genes involved in brain cell function. Disruptions in the expression of these genes could account for the neurodegenerative symptoms seen in Huntington’s disease, including early changes in cognition, says Dr. Ernest Fraenkel, an associate professor of biological engineering at MIT. Dr. Fraenkel’s lab is now investigating the details of how methylation might drive those symptoms, with an eye toward developing potential new treatments. “One could imagine that if we can figure out, in more mechanistic detail, what’s causing these changes in methylation, we might be able to block this process and restore normal levels of transcription early on in the patients,” says Dr. Fraenkel, senior author of a paper describing the findings in this week’s (January 15, 2013) issue of PNAS. Lead author of the paper is Christopher Ng, an MIT graduate student in biological engineering. Other authors are MIT postdoc Ferah Yildirim; recent graduates Yoon Sing Yap, Patricio Velez, and Adam Labadorf; technical assistants Simona Dalin and Bryan Matthews; and Dr. David Housman, the Virginia and D.K. Ludwig Professor of Biology.
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