Reactivation of FMR1 gene expression is a promising strategy for fragile X syndrome therapy


Fragile X syndrome (FXS) is the most common form of intellectual disability and autism spectrum disorder and is caused by CGG repeat expansion in the promoter region of the FMR1 gene, which encodes fragile X mental retardation protein. This event leads to gene silencing and the loss of gene products through DNA methylation and chromatin remodeling. Due to the pathogenesis of FXS, targeted, symptomatic, and etiological approaches have been developed for its treatment. Despite their rapid development, symptomatic and targeted treatment approaches have numerous limitations; etiological approaches have the greatest potential because they affect the main causes of transcriptional silencing. In this review, we consider three potential etiological therapeutic methods that affect the reactivation of FMR1 gene expression: treatment with inhibitors of chromatin-modifying enzymes, the use of noncoding RNAs and the application of gene therapy. Inhibitors of chromatin-modifying enzymes are not clinically applicable because of their low reactivity and high cytotoxicity, and noncoding RNAs are currently only under study. Thus, we discuss gene therapy as the most promising approach for treating FXS in the near future.

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Fig. 1: Therapeutic agents used for FMR1 gene reactivation.


  1. 1.

    Hagerman RJ, Berry-Kravis E, Hazlett HC, Bailey DB, Moine H, Kooy RF, et al. Fragile X syndrome. Nat Rev Dis Primers. 2017;3:17065.

    PubMed  Google Scholar 

  2. 2.

    Haenfler JM, Skariah G, Rodriguez CM, Monteiro da Rocha A, Parent JM, Smith GD, et al. Targeted reactivation of FMR1 transcription in fragile X syndrome embryonic stem cells. Front Mol Neurosci. 2018;11:1–17.

    Google Scholar 

  3. 3.

    Maddalena A, Richards CS, McGinniss MJ, Brothman A, Desnick RJ, Grier RE, et al. Technical standards and guidelines for fragile X: the first of a series of disease-specific supplements to the standards and guidelines for clinical genetics laboratories of the American College of Medical Genetics. Genet Med. 2001;3:200–5.

    CAS  PubMed  PubMed Central  Google Scholar 

  4. 4.

    Jiraanont P, Kumar M, Tang HT, Espinal G, Hagerman PJ, Hagerman RJ, et al. Size and methylation mosaicism in males with fragile X syndrome. Expert Rev Mol Diagn. 2017;17:1023–32.

    CAS  PubMed  PubMed Central  Google Scholar 

  5. 5.

    Luo SY, Wu LQ, Duan RH. Molecular medicine of fragile X syndrome: based on known molecular mechanisms. World J Pediatr. 2016;12:19–27.

    CAS  PubMed  Google Scholar 

  6. 6.

    Tabolacci E, Palumbo F, Nobile V, Neri G. Transcriptional reactivation of the FMR1 gene. A possible approach to the treatment of the fragile X syndrome. Genes. 2016;7:1–16.

    Google Scholar 

  7. 7.

    Holoch D, Moazed D. RNA-mediated epigenetic regulation of gene expression. Nat Rev Genet. 2015;16:71–84.

    CAS  PubMed  PubMed Central  Google Scholar 

  8. 8.

    Xie N, Gong H, Suhl JA, Chopra P, Wang T, Warren ST. Reactivation of FMR1 by CRISPR/Cas9-mediated deletion of the expanded CGG-repeat of the fragile X chromosome. PLoS One. 2016;11:1–12.

    Google Scholar 

  9. 9.

    Park CY, Halevy T, Lee DR, Sung JJ, Lee JS, Yanuka O, et al. Reversion of FMR1 methylation and silencing by editing the triplet repeats in fragile X iPSC-derived neurons. Cell Rep. 2015;13:234–41.

    CAS  PubMed  Google Scholar 

  10. 10.

    Howes OD, Group EPF, Rogdaki M, Findon JL, Wichers RH, Charman T, et al. Autism spectrum disorder: consensus guidelines on assessment, treatment and research from the British Association for Psychopharmacology. J Psychopharmacol. 2018;32:3–29.

    PubMed  Google Scholar 

  11. 11.

    Huber KM, Gallagher SM, Warren ST, Bear MF. Altered synaptic plasticity in a mouse model of fragile X mental retardation. Proc Natl Acad Sci. 2002;99:7746–50.

    CAS  PubMed  Google Scholar 

  12. 12.

    Sabanov V, Braat S, D’Andrea L, Willemsen R, Zeidler S, Rooms L, et al. Impaired GABAergic inhibition in the hippocampus of Fmr1 knockout mice. Neuropharmacology. 2017;116:71–81.

    CAS  PubMed  Google Scholar 

  13. 13.

    Braat S, D’Hulst C, Heulens I, de Rubeis S, Mientjes E, Nelson DL, et al. The GABAA receptor is an FMRP target with therapeutic potential in fragile X syndrome. Cell Cycle. 2015;14:2985–95.

    CAS  PubMed  PubMed Central  Google Scholar 

  14. 14.

    Zerbi V, Markicevic M, Gasparini F, Schroeter A, Rudin M, Wenderoth N. Inhibiting mGluR5 activity by AFQ056/Mavoglurant rescues circuit-specific functional connectivity in Fmr1 knockout mice. Neuroimage. 2019;191:392–402.

    CAS  PubMed  Google Scholar 

  15. 15.

    Cogram P, Deacon RMJ, Warner-Schmidt JL, von Schimmelmann MJ, Abrahams BS, During MJ. Gaboxadol normalizes behavioral abnormalities in a mouse model of fragile X syndrome. Front Behav Neurosci. 2019;13:1–9.

    Google Scholar 

  16. 16.

    Saldarriaga W, Tassone F, González-Teshima LY, Forero-Forero JV, Ayala-Zapata SHR. Fragile X syndrome. Colomb Med. 2014;45:190–8.

    PubMed  PubMed Central  Google Scholar 

  17. 17.

    Pietrobono R. Quantitative analysis of DNA demethylation and transcriptional reactivation of the FMR1 gene in fragile X cells treated with 5-azadeoxycytidine. Nucleic Acids Res. 2002;30:3278–85.

    CAS  PubMed  PubMed Central  Google Scholar 

  18. 18.

    Tabolacci E, Mancano G, Lanni S, Palumbo F, Goracci M, Ferrè F, et al. Genome-wide methylation analysis demonstrates that 5-aza-2-deoxycytidine treatment does not cause random DNA demethylation in fragile X syndrome cells. Epigenetics Chromatin. 2016;9:1–15.

    Google Scholar 

  19. 19.

    Christman JK. 5-azacytidine and 5-aza-2′-deoxycytidine as inhibitors of DNA methylation: mechanistic studies and their implications for cancer therapy. Oncogene. 2002;21:5483–95.

    CAS  PubMed  Google Scholar 

  20. 20.

    Vershkov D, Fainstein N, Suissa S, Golan-Lev T, Ben-Hur T, Benvenisty N. FMR1 reactivating treatments in Fragile X iPSC-derived neural progenitors in vitro and in vivo. Cell Rep. 2019;26:2531–9.e4.

    CAS  PubMed  Google Scholar 

  21. 21.

    Chiurazzi P, Pomponi MG, Pietrobono R, Bakker CE, Neri G, Oostra BA. Synergistic effect of histone hyperacetylation and DNA demethylation in the reactivation of the FMR1 gene. Hum Mol Genet. 1999;8:2317–23.

    CAS  PubMed  Google Scholar 

  22. 22.

    Dolskiy AA, Pustylnyak VO, Yarushkin AA, Lemskaya NA, Yudkin DV. Inhibitors of histone deacetylases are weak activators of the FMR1 gene in fragile X syndrome cell lines. Biomed Res Int. 2017;2017:1–6.

    Google Scholar 

  23. 23.

    Lozano R, Azarang A, Wilaisakditipakorn T, Hagerman RJ. Fragile X syndrome: a review of clinical management. Intractable Rare Dis Res. 2016;5:145–57.

    PubMed  PubMed Central  Google Scholar 

  24. 24.

    Liu T, Wan RP, Tang LJ, Liu SJ, Li HJ, Zhao QH, et al. A microRNA profile in Fmr1 knockout mice reveals microRNA expression alterations with possible roles in fragile X syndrome. Mol Neurobiol. 2015;51:1053–63.

    CAS  PubMed  Google Scholar 

  25. 25.

    Edbauer D, Neilson JR, Foster KA, Wang C-F, Seeburg DP, Batterton MN, et al. Regulation of synaptic structure and function by FMRP-associated microRNAs miR-125b and miR-132. Neuron. 2010;65:373–84.

    CAS  PubMed  PubMed Central  Google Scholar 

  26. 26.

    DeMarco B, Stefanovic S, Williams A, Moss KR, Anderson BR, Bassell GJ, et al. FMRP—G-quadruplex mRNA—miR-125a interactions: implications for miR-125a mediated translation regulation of PSD-95 mRNA. PLoS ONE. 2019;14:1–24.

    Google Scholar 

  27. 27.

    Jin P, Alisch RS, Warren ST. RNA and microRNAs in fragile X mental retardation. Nat Cell Biol. 2004;6:1048–53.

    CAS  PubMed  Google Scholar 

  28. 28.

    Suhl JA, Muddashetty RS, Anderson BR, Ifrim MF, Visootsak J, Bassell GJ, et al. A 3′ untranslated region variant in FMR1 eliminates neuronal activity-dependent translation of FMRP by disrupting binding of the RNA-binding protein HuR. Proc Natl Acad Sci. 2015;112:E6553–61.

    CAS  PubMed  Google Scholar 

  29. 29.

    Lin S. MicroRNAs and Fragile X Syndrome. In: Santulli G, editor. MicroRNA: Medical Evidence. From Molecular Biology to Clinical Practice. 1st ed. Switzerland: Springer International Publishing; 2015. p. 107–21.

  30. 30.

    Wang C, Ge L, Wu J, Wang X, Yuan L. MiR-219 represses expression of dFMR1 in Drosophila melanogaster. Life Sci. 2019;218:31–7.

    CAS  PubMed  Google Scholar 

  31. 31.

    Han P, Chang CP. Long non-coding RNA and chromatin remodeling. RNA Biol. 2015;12:1094–8.

    PubMed  PubMed Central  Google Scholar 

  32. 32.

    Pastori C, Peschansky VJ, Barbouth D, Mehta A, Silva JP, Wahlestedt C. Comprehensive analysis of the transcriptional landscape of the human FMR1 gene reveals two new long noncoding RNAs differentially expressed in Fragile X syndrome and Fragile X-associated tremor/ataxia syndrome. Hum Genet. 2014;133:59–67.

    CAS  PubMed  Google Scholar 

  33. 33.

    Rupaimoole R, Slack FJ. MicroRNA therapeutics: towards a new era for the management of cancer and other diseases. Nat Rev Drug Discov. 2017;16:203–21.

    CAS  PubMed  Google Scholar 

  34. 34.

    Hoy SM. Onasemnogene abeparvovec: first global approval. Drugs. 2019;79:1255–62.

    CAS  PubMed  Google Scholar 

  35. 35.

    Gantois I, Bakker C, Reyniers E, Willemsen R, DHooge R, De Deyn P, et al. Restoring the phenotype of fragile X syndrome: insight from the mouse model. Curr Mol Med. 2001;1:447–55.

    CAS  PubMed  Google Scholar 

  36. 36.

    Musumeci SA, Calabrese G, Bonaccorso CM, D’Antoni S, Brouwer JR, Bakker CE, et al. Audiogenic seizure susceptibility is reduced in fragile X knockout mice after introduction of FMR1 transgenes. Exp Neurol. 2007;203:233–40.

    CAS  PubMed  Google Scholar 

  37. 37.

    Peier AM, McIlwain KL, Kenneson A, Warren ST, Paylor R, Nelson DL. (Over)correction of FMR1 deficiency with YAC transgenics: behavioral and physical features. Hum Mol Genet. 2000;9:1145–59.

    CAS  PubMed  Google Scholar 

  38. 38.

    Zeier Z, Kumar A, Bodhinathan K, Feller JA, Foster TC, Bloom DC. Fragile X mental retardation protein replacement restores hippocampal synaptic function in a mouse model of fragile X syndrome. Gene Ther. 2009;16:1122–9.

    CAS  PubMed  PubMed Central  Google Scholar 

  39. 39.

    Gholizadeh S, Arsenault J, Xuan IC, Pacey LK, Hampson DR. Reduced phenotypic severity following adeno-associated virus-mediated Fmr1 gene delivery in fragile X mice. Neuropsychopharmacology. 2014;39:3100–11.

    CAS  PubMed  PubMed Central  Google Scholar 

  40. 40.

    Arsenault J, Gholizadeh S, Niibori Y, Pacey LK, Halder SK, Koxhioni E, et al. FMRP expression levels in mouse central nervous system neurons determine behavioral phenotype. Hum Gene Ther. 2016;27:982–96.

    CAS  PubMed  PubMed Central  Google Scholar 

  41. 41.

    Liu XS, Wu H, Krzisch M, Wu X, Graef J, Muffat J, et al. Rescue of fragile X syndrome neurons by DNA methylation editing of the FMR1 gene. Cell. 2018;172:979–92.e6.

    CAS  PubMed  PubMed Central  Google Scholar 

  42. 42.

    Lee B, Lee K, Panda S, Gonzales-Rojas R, Chong A, Bugay V, et al. Nanoparticle delivery of CRISPR into the brain rescues a mouse model of fragile X syndrome from exaggerated repetitive behaviours. Nat Biomed Eng. 2018;2:497–507.

    CAS  PubMed  PubMed Central  Google Scholar 

  43. 43.

    Foss DV, Wilson RC. Emerging strategies for genome editing in the brain. Trends Mol Med. 2018;24:822–4.

    CAS  PubMed  Google Scholar 

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The reported study was funded by the Russian Foundation for Basic Research (RFBR) under research project 18-29-07033.

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Correspondence to Dmitry V. Yudkin.

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Shitik, E.M., Velmiskina, A.A., Dolskiy, A.A. et al. Reactivation of FMR1 gene expression is a promising strategy for fragile X syndrome therapy. Gene Ther 27, 247–253 (2020).

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