Fragile X syndrome (FXS), the leading genetic cause of intellectual disability, arises from FMR1 gene silencing and the subsequent loss of the RNA-binding protein FMRP. N6-methyladenosine (m6A) is a prevalent mRNA modification essential for post-transcriptional regulation. FMRP binds and regulates the stability of m6A-containing transcripts. However, how FMRP deficiency impacts transcriptome-wide m6A modifications in FXS remains unknown. To address this, we generated cortical neurons from induced pluripotent stem cells (iPSCs) derived from healthy individuals and FXS patients. Electrophysiology recordings revealed synaptic and neuronal network defects in FXS iPSC-derived neurons. Transcriptome-wide analysis revealed striking m6A hypermethylation predominantly affecting synapse-associated transcripts. Mechanistically, we demonstrated that FMRP deficiency drives the aberrant translational upregulation of core m6A writers, a causal relationship definitively validated using CGG-corrected isogenic control lines. Targeted genetic knockdown of the m6A writer METTL3 successfully rescued synaptic phenotypes in FXS neurons, whereas its overexpression in control neurons phenocopied these synaptic defects, confirming the causal role of m6A dysregulation in FXS pathology. Notably, pharmacological intervention with the METTL3 inhibitor STM-2457 normalized methylation on synapse-associated transcripts and restored synaptic transmission in FXS neurons. Together, our findings uncover an FMRP-dependent epitranscriptomic mechanism contributing to FXS pathogenesis and suggest a promising avenue for m6A-targeted therapies.
Fragile X Syndrome (FXS) is the most common inherited form of intellectual disability. It is caused by a trinucleotide expansion in the 5' UTR of the Fragile X messenger ribonucleoprotein 1 (FMR1) gene leading to loss of expression of Fragile X messenger ribonucleoprotein (FMRP). There is currently no cure for FXS. We developed an FMR1 gene therapy based on an adeno-associated viral vector designed with strong translational potential for future clinical testing. The viral vector was tested in Fmr1 knockout mice using two translationally relevant delivery routes and ages corresponding to in utero, toddler, and adolescent ages in humans. Functional studies showed that the FMR1 gene therapy improved select translational FXS phenotypes spanning three critical domains: sensory hyperexcitability, adaptation to change, and altered brain activity. Expression after intracerebroventricular injection was most prominent in the forebrain, whereas intravenous delivery predominantly led to expression across midbrain and brainstem, suggesting that a dual route may be needed to achieve full brain coverage. Biodistribution analyses further suggested that FMRP expression must be titrated carefully for optimal rescue. In summary, we show that FMR1 gene therapy using delivery routes and vehicles approved for clinical use improves core phenotypes in a mouse model for FXS.
Richard K Lacher, Kari Henson, Lindsay N Wathen et al.· Gene Therapy· 0 citations
Findings link a population-enriched missense variant to disrupted chromatin regulation, genome stability, and neurodevelopmental timing, bridging human genetic risk with cellular pathophysiology.
R. Lease, Rediet T. Oshone, Yumna Ahmed et al.· Research Square· 0 citations
The discovery of a family with six affected members carrying a heterozygous loss- of-function variant in INTS6 highlights the critical role of INTS6 in transcriptional regulation of human neurodevelopment and reinforces its association with NDDs.
Nelli Jalkanen, K. Trontti, Antto J. Norppa et al.· bioRxiv· 0 citations
Schizophrenia (SCZ) is a genetically complex neuropsychiatric disorder in which rare loss-of-function mutations in the histone methyltransferase SETD1A confer substantial risk. Although SETD1A haploinsufficiency had been linked to morphological, synaptic and behavioral abnormalities in the prefrontal cortex, whether and how SETD1A coordinates transcriptional and functional programs across different brain regions remains unknown. Here, we delineate the brain region-specific effects of SETD1A-associated dysfunction using conditional Setd1a knockout mice. We find that the dorsal striatum (dStr) and mediodorsal thalamus (MD) exhibit distinct transcriptomic and neuronal alterations to those in the PFC, and show transcriptomic enrichment for other SCZ risk genes. Loss of Setd1a in the dStr or MD drives selective vulnerability in key behavioral assays, suggesting important roles for these brain regions in the etiology of SCZ. By screening 6 existing H3K4 demethylase inhibitors, we identify the LSD1 (KDM1A) inhibitor TAK-418 as a potent modulator capable of restoring H3K4me3 levels and gene expression, as well as rescuing synaptic and SCZ-like behavioral phenotypes in the Setd1a+/− mice. Thus, our work provides a mechanistic link between high-penetrance SETD1A variants and region-specific brain dysfunction, establishing a framework for connecting rare loss-of-function variation in chromatin regulators to multidimensional neuropsychiatric phenotypes.
ASXL3 patient truncations in neurodevelopmental condition Bainbridge-Ropers syndrome are shown to mediates gain-of-function (GOF) by escaping nonsense-mediated decay and Cullin 4-dependent degradation, resulting in aberrant protein accumulation, widespread transcriptional dysregulation, and altered chromatin accessibility.
Y. Nakamura, T. Nguyen, N. Mor et al.· medRxiv· 0 citations