None approved for ASO; preclinical research stage
Fragile X syndrome is the most common inherited cause of intellectual disability and the most common known single-gene cause of autism spectrum disorder. It is caused by a CGG trinucleotide repeat expansion in the 5′ untranslated region of the FMR1 gene on the X chromosome. Normal individuals have 5–44 CGG repeats; the full mutation has over 200 repeats, which triggers hypermethylation of the FMR1 promoter and transcriptional silencing of the gene. The result is absence of FMRP (Fragile X Messenger Ribonucleoprotein), a protein essential for synaptic plasticity and normal neuronal development.
Fragile X syndrome presents with mild to moderate intellectual disability, developmental delays, anxiety, attention problems, and sometimes autism spectrum behaviors. Physical features can include a long face, prominent ears, and macroorchidism (enlarged testicles) in post-pubertal males. The condition affects males more severely than females because males have only one X chromosome. Females, with two X chromosomes, typically have one functional FMR1 allele and generally present with milder symptoms.
The disease mechanism in Fragile X is gene silencing through epigenetic modification. The CGG repeat expansion triggers DNA methylation and heterochromatin formation at the FMR1 promoter, shutting down transcription. Unlike Huntington’s disease or myotonic dystrophy, where the repeat expansion produces a toxic RNA or protein, the Fragile X repeat simply silences the gene. The FMR1 coding sequence downstream of the repeat is intact — if the epigenetic silencing could be reversed, the gene could produce functional FMRP.
This makes Fragile X syndrome a potential target for ASO-mediated gene reactivation. Preclinical research has explored ASOs designed to target the expanded CGG repeat or the regulatory elements that maintain silencing, with the goal of disrupting the heterochromatin structure and allowing transcription to resume. Studies in cell culture models have shown that targeting the FMR1 mRNA or the CGG repeat region with ASOs can partially restore FMRP expression.
The challenges for ASO therapy in Fragile X include CNS delivery (FMRP is primarily needed in the brain), the extent of epigenetic silencing (which involves multiple layers of chromatin modification), and the need for sustained treatment to maintain gene reactivation. Intrathecal delivery, similar to what is used for Spinraza and Tofersen, is a potential route.
Pequliar designs ASO candidates for Fragile X syndrome, targeting the CGG repeat region or associated regulatory elements to promote FMR1 gene reactivation. The platform scores candidates for binding affinity, structural accessibility, and off-target safety, providing synthesis-ready sequences for preclinical research and evaluation. Given the complexity of epigenetic silencing in Fragile X, experimental validation is essential to assess the degree of reactivation achievable.
Describe your mutation and get ranked, synthesis-ready ASO candidates in minutes. $399 per design.
Start a designPequliar is a computational research tool for informational purposes only. All sequences are computationally predicted candidates that have not been experimentally validated. Pequliar does not prescribe, recommend, or administer any compound. Independent validation by qualified professionals is required.