ASO Rescue of FMR1 Mis-Splicing in Neurons and Mitigation of Fragile X Molecular Deficits
Joel Richter, PhD
Co-Principal Investigator
Sneha Shah, PhD
Co-Principal Investigator
UMass Chan Medical School
Worcester, MA
2025-2026 Grant Funding: $200,000
Supported through FRAXA’s Curative Therapies Fund
Summary
With previous grants from FRAXA, Dr. Richter's team made a fundamental discovery that redefines Fragile X syndrome. The gene, FMR1, which was thought to be completely silenced in Fragile X syndrome, is actually active in most individuals, producing a version of its RNA which does not function normally. This discovery led the team to the idea of designing antisense oligonucleotides (ASOs) to target this RNA to treat Fragile X syndrome.
This project targets a faulty version of FMR1 RNA (FMR1-217) found in many individuals with Fragile X. Researchers will use antisense oligonucleotides (ASOs) to correct this splicing error and restore production of the missing protein in iPSC-derived neurons and brain organoids.
They’ll also investigate widespread metabolic disruptions seen in human FXS brain tissue and cells — but not in mice — to explore potential biomarkers for treatment response. This work could pave the way for disease-modifying therapies and better tools to track their effectiveness.
The Science
by Sneha Shah, PhD, and Joel Richter, PhD
The leading inherited intellectual disorder is Fragile X syndrome (FXS), which lies on the autism spectrum. FXS is caused by a nucleotide repeat expansion in the FMR1 gene, which induces gene methylation, transcriptional silencing, and loss of the gene product, FMRP. The absence of FMRP causes the many pathological manifestations of Fragile X syndrome.
FMRP is an RNA binding protein that inhibits translation of many proteins by stalling ribosomes on mRNAs. One mRNA bound by FMRP-stalled ribosomes is Setd2 which encodes an epigenetic modifier that in turn indirectly alters pre-mRNA splicing. Based on this, we sequenced and analyzed splicing in white blood cells from 29 individuals with Fragile X syndrome and 13 typically developing individuals, and we found hundreds of statistically significant splicing changes. Surprisingly, FMR1 RNA was expressed in 72% of FXS samples, even in the samples where the gene was fully methylated with no mosaicism. Furthermore, exclusively in the FXS samples, FMR1 RNA itself was mis-spliced to a specific form that included a pseudo-exon. This was also the case in Fragile X syndrome postmortem brain.
We tiled antisense oligonucleotides (ASOs) across the mis-spliced region and found that two of them reduced improper FMR1 splicing, restored proper FMR1 splicing, and most importantly, restored FMRP to normal levels.
With this grant from FRAXA, we will develop human cerebral organoids from Fragile X syndrome individuals. With these organoids, we will investigate FMR1 mis-splicing and ASO restoration of proper splicing and FMRP, and rescue mitochondrial/metabolomic dysregulation. Experiments in this project are essential steps toward possible ASO therapeutics to treat Fragile X syndrome.
The Next Steps
- QurAlis has licensed the Richter lab’s discoveries pointing to ASO treatment for Fragile X.
- QurAlis is now advancing this research with additional preclinical studies to prepare for Fragile X clinical trials.
- QurAlis and Quiver Biosciences, both based in Cambridge, MA, are collaborating to refine this therapeutic approach.
- FRAXA has awarded an additional grant to Quiver Biosciences to accelerate these essential studies.
See also:
Innovative Breakthrough in Fragile X Treatment: The Promise of Antisense Oligonucleotide (ASO) Therapy — Dr. Michael Tranfaglia explains the transformative potential of ASO therapy and how this innovative approach is reshaping Fragile X research.
