Research ArticleFragile X Syndrome

Epigenetic Modification of the FMR1 Gene in Fragile X Syndrome Is Associated with Differential Response to the mGluR5 Antagonist AFQ056

Science Translational Medicine  05 Jan 2011:
Vol. 3, Issue 64, pp. 64ra1
DOI: 10.1126/scitranslmed.3001708

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A Methylation Marker for Fragile X Syndrome

Through the practice of meditation, students of Eastern philosophies are taught to turn down the noise to find the silence within. But for patients suffering from fragile X syndrome, it is the silence within that turns up the noise. In this disorder, a defect in the fragile X mental retardation 1 gene (FMR1) silences its expression, which gives rise to myriad molecular changes, most notably a turning up of signaling through the metabotropic glutamate receptor mGluR5. This noisy signaling pathway contributes to the cognitive deficits and differences that first become apparent in patients during childhood, and currently these symptoms are treatable only with supportive behavioral measures. But in mice and fruit flies that carry the same genetic defects as patients and also show enhanced glutamate receptor signaling and behavioral problems, administration of an mGluR5 antagonist improves the symptoms. Jacquemont et al. have now treated a group of 30 fragile X patients with such an antagonist. Not all subjects showed improvement, but an analysis of those who did revealed that the promoter of the FMR1 gene in drug-responsive patients is fully methylated, a sign that gene expression is completely silenced. This molecular aberration might serve as a signature that defines fragile X patients who could benefit from treatment with mGluR5 antagonists.

In individuals with fragile X syndrome, the FMR1 gene can contain as many as several thousand extra repeats of the triplet base pairs CGG, a distortion that is accompanied by extra methylation at the gene’s promoter and thus impaired transcription. Because the number of triplet repeats differs widely from person to person—and even from generation to generation—there is a broad variation among patients in the structure of the gene and its methylation pattern. So when the authors tested the effects of a newly described mGluR5 inhibitor on fragile X patients, they assayed the methylation status of the FMR1 promoter, as well as running a large battery of behavioral tests designed to detect stereotypic behavior, hyperactivity, and inappropriate speech. In this clinical trial, the mGluR5 antagonist had no effect on the behaviors measured by these primary tests, but administration of the drug did correlate with differences observed in a secondary collection of tests, when the drug-treated patient group was compared with subjects who were given a placebo treatment. In a subsequent exploratory analysis, the authors found that each member of the subgroup of patients who harbored fully methylated FMR1 promoters showed improvement by the primary behavioral measures, exhibiting a boost in performance 19 or 20 days after treatment was started. The patient group with partially methylated promoters showed no such changes.

This correlation between response to treatment and methylation status of the FMR1 promoter provides the basis for a larger study, appropriately designed to test whether methylation can serve as a predictor of a positive antagonist response in a population of patients with fragile X syndrome. It also offers hope that inhibition of the metabotropic glutamate system—believed to underlie many of the characteristic behaviors associated with fragile X—may be accomplished routinely, at least in patients in which the silence within lies in the FMR1 promoter.


  • * These authors contributed equally to this work.

  • Citation: S. Jacquemont, A. Curie, V. des Portes, M. G. Torrioli, E. Berry-Kravis, R. J. Hagerman, F. J. Ramos, K. Cornish, Y. He, C. Paulding, G. Neri, F. Chen, N. Hadjikhani, D. Martinet, J. Meyer, J. S. Beckmann, K. Delange, A. Brun, G. Bussy, F. Gasparini, T. Hilse, A. Floesser, J. Branson, G. Bilbe, D. Johns, B. Gomez-Mancilla, Epigenetic Modification of the FMR1 Gene in Fragile X Syndrome Is Associated with Differential Response to the mGluR5 Antagonist AFQ056. Sci. Transl. Med. 3, 64ra1 (2011).