The three genes under investigation sit at the heart of synaptic plasticity, the molecular machinery that allows connections between neurons to strengthen or weaken with experience. FMR1 mutations cause Fragile X syndrome, an inherited condition affecting roughly 1 in 4,000 males and 1 in 7,000 females, in which a CGG repeat expansion on the X chromosome silences production of the FMRP protein. FMRP is strongly expressed in neurons of the cortex, hippocampus, thalamus, and cerebellum, and its loss disrupts spine formation and pruning, synaptic plasticity, and protein synthesis. SYNGAP1, by contrast, encodes a protein found in the postsynaptic density, and mutations of this gene account for up to 1 percent of all non-syndromic intellectual disability. GRIN2B governs expression of the GluN2B subunit of the NMDA receptor, a molecular gatekeeper of plasticity itself. All three conditions are associated with IQs of 70 or below in affected males, making them among the most consequential monogenic causes of cognitive impairment known.

Yet when scientists have tried to reproduce these human deficits in rodents, the results have been maddeningly inconsistent. Studies of Fmr1 knockout mice have reported everything from modest water maze impairments to no deficits at all, depending on strain, task, and laboratory. Fmr1 knockout rats have fared no more clearly: one study found fewer platform crossings during probe trials but no difference in quadrant occupancy, while another found no impairment whatsoever in reference memory, reversal learning, or delayed matching to place. The picture in SYNGAP1 models is somewhat more consistent in mice, with impairments reported on T-maze alternation, Barnes maze learning, and water maze probe preference — but even here, some studies found deficits only during the first 15 seconds of a probe trial, with mutant and wild-type mice converging over the full 60 seconds. GRIN2B rodent work has been similarly split, with one mouse study showing impairments in long-term potentiation, long-term depression, and maze performance, while another found no water maze deficits despite a 30 to 50 percent reduction in GluN2B expression.

The research team, led by Anuj Vadher and Paul Dudchenko, suspected that part of the problem lay in the testing paradigm itself. In the traditional Morris water maze, rats swim in a pool of opaque water searching for a submerged platform, using visual landmarks scattered around the laboratory room. But which landmarks the animals actually use — a lantern, a poster, a curtain edge — is assumed rather than demonstrated. The team had recently observed that head direction cells, neurons that putatively underpin the rodent’s sense of direction, show significant alterations in Fmr1 knockout rats. A task that taps the animals’ use of directional information might therefore be especially sensitive to deficits in this model. To make the task genuinely informative, they built a variant in which the only visual landmarks available were four specified objects — a lantern, a white board, a hi-vis jacket, and a sombrero hat — hung on black curtains surrounding the pool. Critically, at the start of each day, the landmarks and the platform were rotated together by a pseudorandom angle, dissociating the platform’s location from any uncontrolled cues in the testing room and rendering the specified landmarks the only reliable external guides.

The pilot work also revealed an unexpected behavioral wrinkle. When tested in an open pool, both mutant and wild-type Fmr1 rats developed an annular search strategy, swimming in circles at roughly the correct distance from the pool walls rather than relying on the landmarks. Radial band analysis confirmed that this ring-search preference was statistically significant in both genotypes. Such a strategy requires no landmark learning at all — the animals simply learn the platform’s distance from the walls. To force genuine landmark use, the team added eight transparent acrylic triangular wall inserts to the pool, dividing it into eight alleyways that opened into a central circle. Now the rats could not simply swim in a ring; they had to swim into and out of each alleyway, making the search far more costly and the use of directional information far more apparent.

Across 10 days of training in this directional water maze, all three mutant models learned the task robustly. Fmr1 knockout rats and their wild-type littermates both showed steep decreases in the time needed to find the hidden platform, and in the platform-removal probe trials — in which the platform stayed submerged and held down by magnets for 60 seconds — both groups showed increasing preference for the target octant, the alleyway containing the platform’s direction. By day 4, both genotypes performed significantly above the 12.5 percent chance level. Remarkably, the Fmr1 knockout rats actually showed a small but significant advantage over wild-type animals in acquisition speed, though the authors attribute this to unusually slow wild-type performance on day 3. In the more robust measure of octant bias during probe sessions, there was no difference between the groups at all.

The Syngap1 heterozygous rats told a similar story, with one nuance. Across two cohorts totaling 8 mutant and 11 wild-type animals, both groups learned the platform direction equally well, with no difference in probe trial octant occupancy. Mutant rats did take slightly longer to find the platform during training — a significant overall genotype effect — but this latency difference never translated into a memory deficit when the platform was removed. The Grin2b heterozygous rats, tested with both males and females, were indistinguishable from wild-type littermates in every measure, and both groups showed significant target octant preference as early as day 2, the fastest learning of any model tested. For a gene whose product directly gates NMDA receptor currents — the very substrate of long-term potentiation — the intact performance is perhaps the most surprising result of the study.

The landmark removal probes delivered the study’s most conceptually significant finding. When three of the four trained landmarks were removed, leaving only one, performance remained above chance for almost every group and almost every landmark, with the exception of the Syngap1 rats, whose preference approached but did not reach statistical significance. Crucially, within each session, some individual animals performed at or below chance while others showed more than 80 percent occupancy of the correct octant. This pattern is inconsistent with configural learning, in which animals triangulate the platform using the full geometry of the landmark array — that strategy would have impaired all animals equally when only one cue remained. Instead, it suggests that different rats had learned directional associations with different individual landmarks, and that each animal’s performance depended on which specific cue happened to survive the deletion. The authors liken this to pattern completion, the same process that keeps hippocampal place fields intact when only a subset of trained landmarks is available.

The implications cut both ways. On one hand, the intact landmark learning in all three models — despite mutations that disrupt RNA binding, postsynaptic signaling, and receptor subunit expression — suggests that basic associative processes are spared in these genetic conditions, and that higher-order tasks involving sensory conflict may be needed to reveal the deficits that clearly exist in affected humans. When a single source of information is sufficient to guide performance, inflexibility in integrating other sensory streams may simply never become apparent. On the other hand, the finding that rats may navigate by individual landmarks rather than landmark configurations — at least in a directional water maze — revises a central assumption of spatial learning research that has gone largely untested for decades. For a field that has long treated the water maze as a window into cognitive map formation, the message is sobering: what looks like map-based navigation may sometimes be a collection of simple stimulus-response associations, each animal carrying its own private compass needle pointed at a single familiar object.

Subject of Research: Intact spatial learning in Fmr1–/y, Syngap1+/–, and Grin2b+/– rat models of neurodevelopmental disorders

Article Title: Intact spatial learning in Fmr1–/y, Syngap1+/–, and Grin2b+/– rat models of neurodevelopmental disorders

Article References: Vadher, A., Duszkiewicz, A. J., Wood, E. R., & Dudchenko, P. A. (2026). Intact spatial learning in Fmr1–/y, Syngap1+/–, and Grin2b+/– rat models of neurodevelopmental disorders. Frontiers in Behavioral Neuroscience, 20, Article 1929983. https://doi.org/10.3389/fnbeh.2026.1929983

Image Credits: AI Generated

DOI: 10.3389/fnbeh.2026.1929983

Keywords: Intact, spatial, learning, Fmr1, Syngap1, Grin2b, models, neurodevelopmental, disorders, scientific research

The research team, led by investigators at the Icahn School of Medicine at Mount Sinai and the University of California, Davis, analyzed postmortem prefrontal cortex tissue from 27 men with FXTAS and 29 male controls. All samples came from Brodmann area 9, the same region where the disorder’s molecular damage plays out in life. Female donors were deliberately excluded to avoid the confounding influence of X-chromosome inactivation, given that FMR1 itself resides on the X chromosome. Diagnosis in each FXTAS case was confirmed by the presence of the premutation allele and, in many cases, by the hallmark ubiquitin-positive intranuclear inclusions seen under the microscope after death.

Technically, the work was demanding. The team profiled methylation using two versions of the Illumina MethylationEPIC array, version one covering roughly 850,000 probes and version two roughly 900,000, and merged the datasets by retaining the 718,960 CpG probes common to both platforms. To guard against hidden confounders, from batch effects to differences in postmortem interval, they applied surrogate variable analysis, a statistical framework that estimates unmeasured sources of variation and adjusts for them while protecting disease status from being inadvertently scrubbed out of the data. As a sensitivity check, the entire analysis was repeated with methylation beta values converted to M values; effect sizes and adjusted p values from the two approaches correlated at roughly 0.98 and 0.95, respectively, indicating that the findings were not artifacts of the statistical parameterization.

Using a strict definition that required both a methylation difference greater than 0.10 on the beta scale and a false discovery rate below 0.05, the team identified 98 differentially methylated positions, 48 hypermethylated and 50 hypomethylated, mapping to 70 genes. That number may sound modest against the hundreds of thousands of probes tested, but individual CpG sites are noisy messengers, and the fact that any signal survived the thresholds at all is notable for a rare, late-onset disorder. Moreover, several genes carried multiple, directionally consistent changes, which boosted confidence in those loci.

The genes themselves read like a map of processes that neuroscientists already suspect in FXTAS. CYP2E1, a cytochrome P450 enzyme that is a major enzymatic source of reactive oxygen species in neurons and astrocytes, carried three hypomethylated probes in FXTAS. LINGO1, a negative regulator of myelination and oligodendrocyte differentiation and a known genetic risk factor for essential tremor, was hypomethylated, a finding that resonates with the prominent white matter disease of FXTAS. Hypomethylation also touched the zinc importer SLC39A4 and the cerebellar zinc-finger transcription factor ZIC1, pointing toward altered zinc homeostasis, a theme linked to mitochondrial dysfunction and antioxidant defense in neurodegeneration. Genes governing synaptic function, including ADD2 and SYT3, and chromatin regulators such as RCOR1 and PRDM16 appeared as well.

The single most striking immune-related finding was TRAF3, which contains one of the most statistically significant methylation changes in the entire dataset. TRAF3 acts as a brake on non-canonical NF-κB signaling and type I interferon responses, so hypermethylation at this locus, if it dampens expression, could loosen a critical restraint on inflammatory signaling. The directional pattern among other immune genes was equally intriguing: negative regulators such as TRAF3 and the lectin receptor CLEC1A were hypermethylated, while genes promoting myeloid activation and inflammatory effector function, including RHBDF2/iRhom2, which controls TNF-α shedding, the myeloid transcription factor MEIS1, and the phagocytosis regulator ELMO3, were hypomethylated. Notably, no large methylation changes appeared at the FMR1 locus itself, consistent with the premutation state, in which the promoter remains largely unmethylated unlike the full mutation seen in fragile X syndrome.

Pathway analyses gave biological texture to these gene-level hits, though the authors are careful about their limits. Reactome analysis highlighted themes of inflammatory resolution, including biosynthesis of maresin-like pro-resolving mediators, axonal growth inhibition through RHOA signaling, zinc influx via the SLC39 family, and CYP2E1 metabolism. None of these pathways survived correction for multiple testing, and transcription-factor motif enrichment and protein-protein interaction analyses likewise found no significant higher-order modules, although AP-1/bZIP family motifs, relevant to innate immune responses, ranked nominally at the top in both HOMER and JASPAR sequence analyses. Comparison with published brain methylation signatures of Alzheimer’s, Parkinson’s, and Huntington’s disease found no gene-level overlap, while seven of the FXTAS-associated genes did overlap with differentially expressed genes in an independent mouse model of the disorder.

The proteomic arm of the study delivered the most dramatic result. Using the Olink Inflammation panel, a proximity extension assay capable of quantifying 366 inflammation-related proteins, the team profiled prefrontal cortex from 9 FXTAS cases and 12 controls. Sixty proteins differed significantly between the groups, and 59 of them, essentially all of them, were less abundant in FXTAS. The depleted proteins included chemokines such as CXCL8 and CXCL10, interleukins including IL6, IL15, and IL18, core components of innate immune and NF-κB signaling such as TLR3, IRAK1, IRAK4, and IKBKG/NEMO, the classical complement component C1QA, and microglial receptors like SIGLEC1 and SIGLEC10. The team then showed through a series of technical checks that this near-uniform reduction was not explained by sequencing depth, normalization behavior, or internal control artifacts.

A reduced inflammatory protein signature in a neurodegenerative disease may seem paradoxical, and the authors do not interpret it as the absence of inflammation. Instead, they propose that the combined epigenetic and proteomic findings may reflect a chronically engaged but dysregulated or inadequately resolved immune state, in which the brakes and the accelerators of innate immunity are both malfunctioning. Supporting this view, an independent mass spectrometry proteomic study of FXTAS cortex from the same UC Davis brain repository had already reported reduced abundance of inflammation-associated proteins, and among the 19 proteins measured by both platforms, 13 showed concordant directionality, including IRAK1, IKBKG/NEMO, and PARP1. The picture is also unlikely to be uniform across the brain: elevated IL-12 and TNF-α have previously been reported in the FXTAS cerebellum, hinting at region-specific inflammatory profiles.

The study has important caveats that the authors openly acknowledge. The methylation data come from bulk tissue, so cell-type-specific effects, particularly glial inflammatory responses, cannot be directly resolved. The work is cross-sectional and cannot establish whether methylation changes precede or follow disease onset. The Olink cohort was small, the assay was restricted to inflammation-related proteins, and methylation changes cannot be assumed to map one-to-one onto gene expression or protein abundance, especially since many differentially methylated sites sat outside promoters. Still, the convergence is what makes this study compelling: methylation alterations in immune-regulatory genes such as TRAF3 sit alongside a proteomic signature of coordinated disruption in innate immune and NF-κB pathways, measured with entirely independent technology. As the first genome-wide methylation map of the FXTAS brain, the work reframes a disorder once seen purely as RNA toxicity, and it hands researchers a set of concrete, testable hypotheses linking CGG-repeat biology to oxidative stress, myelination, zinc homeostasis, and an immune system that appears both fired up and strangely depleted in the same tissue.

Subject of Research: Epigenetic and inflammatory molecular alterations in fragile X-associated tremor/ataxia syndrome brain tissue

Article Title: DNA methylation and proteomic profiling of postmortem brain tissue reveals epigenetic dysregulation and inflammatory signaling in fragile X-associated tremor/ataxia syndrome

Article References: Lozano, R., Lin, X., Hagerman, R., Martínez-Cerdeño, V., & Pinto, D. (2026). DNA methylation and proteomic profiling of postmortem brain tissue reveals epigenetic dysregulation and inflammatory signaling in fragile X-associated tremor/ataxia syndrome. Frontiers in Molecular Neuroscience, 19, Article 1932396. https://doi.org/10.3389/fnmol.2026.1932396

Image Credits: AI Generated

DOI: 10.3389/fnmol.2026.1932396

Keywords: FXTAS, FMR1, DNA methylation, epigenetics, NF-κB signaling, neuroinflammation, TRAF3, CYP2E1, LINGO1, proteomics, Olink, neurodegeneration

The study, led by Walter E. Kaufmann of the Department of Human Genetics at Emory University School of Medicine and Paul S. Horn of the Division of Neurology at Cincinnati Children’s Hospital Medical Center, together with the FORWARD Consortium, drew on the pediatric FORWARD database, a multi-site registry and longitudinal clinical database established to study fragile X syndrome across specialty clinics in the United States. The analytical sample comprised 1,072 males and 338 females, an unusually large cohort for a rare genetic disorder, allowing the researchers to examine patterns of co-occurrence with a statistical power that smaller, single-center studies could not achieve.

The team focused on the eight most common behavioral comorbidities identified by clinicians in these specialty fragile X clinics: attention problems, anxiety, hyperactivity, autism spectrum disorder, mood disturbances, irritability and aggression, self-injurious behavior, and sleep problems. Importantly, the researchers treated these as clinician-identified behavioral concerns rather than formal diagnoses, with one exception. Autism spectrum disorder was the only comorbidity defined using explicit DSM-5 criteria, reflecting the particular diagnostic challenges that autism presents in fragile X syndrome, where the social and repetitive features of the syndrome itself can blur the boundary between behavioral phenotype and co-occurring condition.

Across the cohort, attention problems and anxiety emerged as the two most frequent behavioral comorbidities, and, notably, also as the mildest in terms of functional impact. By contrast, the cluster of disruptive behaviors captured under the umbrella of irritability, aggression, agitation, and self-injurious behavior, while less universally present, carried substantially greater weight in terms of impairment. Roughly half of the children affected by any given behavioral comorbidity showed functional impairment from that condition, a proportion that underscores how often these difficulties cross the threshold from trait to clinically meaningful problem in fragile X syndrome.

The most striking finding concerned co-occurrence. Among children with fragile X syndrome, 69 percent were reported to have impairing behavioral comorbidities occurring together, and 39 percent of those children presented with more than two comorbidities simultaneously. Children with multiple co-occurring conditions showed the greatest overall impairment, a dose-response-like pattern suggesting that the cumulative behavioral load, rather than any single diagnosis, is what most powerfully determines how much a child’s daily functioning is compromised. For families and clinicians, this finding reframes fragile X syndrome not as a condition with one dominant behavioral complication but as one in which multiple behavioral challenges frequently compound one another.

To dissect these patterns, the researchers deployed an unusually rich statistical toolkit. Chi-square analyses quantified how frequently pairs of comorbidities appeared together. Polychoric and polyserial correlations, methods designed to estimate the association between ordinal and continuous variables that underlie observed categorical ratings, allowed the team to measure the strength of association between comorbidities while correcting for the fact that co-occurrence is partly driven by simple frequency. Mann-Whitney tests compared behavioral scale scores between groups. This distinction between frequency-driven co-occurrence and genuine statistical association proved crucial: the researchers found that while which comorbidities co-occur is influenced by how common each one is, the strength of the association between any pair was relatively independent of frequency, implying that some pairings reflect shared underlying mechanisms rather than mere arithmetic.

Two of those strong associations stood out because they replicate well-documented patterns in the general, non-fragile X population. The first was the pairing of attention problems with hyperactivity, a combination familiar from attention deficit-hyperactivity disorder in typical development. The second was the coupling of anxiety with mood disturbances, echoing the extensive literature on comorbidity between anxiety and mood disorders in the general psychiatric population. That these canonical pairings also hold in fragile X syndrome suggests that at least some of the architecture of behavioral comorbidity in this genetic condition mirrors the structure seen in the broader population, even though the underlying biology is profoundly different.

The team also examined how standardized behavioral scale scores related to the clinician-identified comorbidities. Scale scores broadly aligned with other severity parameters, lending convergent validity to the clinician-based classification. However, correlations between comorbidities and specific scales tracked the relevance of the behaviors each scale evaluates, rather than behaving as simple proxies for severity. In other words, a given scale correlated most strongly with the comorbidities whose symptom content it directly captures, a finding that helps clinicians interpret behavioral checklist data in fragile X syndrome with appropriate nuance.

Perhaps the most unexpected result of the entire analysis was the discovery that all eight behavioral comorbidities were strongly correlated with the Sensory problems scale. Sensory difficulties, including hyperarousal to sound, touch, and visual stimuli, have been increasingly recognized as central features of fragile X syndrome, with prior work from the FORWARD registry documenting their prevalence and their links to hyperarousal. But the uniformity of the association across such clinically distinct comorbidities, from attention deficits to aggression to sleep disturbance, was not anticipated. The finding raises the possibility that sensory dysregulation functions as a transdiagnostic factor in fragile X syndrome, a common physiological substrate that feeds into or amplifies virtually every major behavioral problem the condition produces. If confirmed by future longitudinal work, this would carry direct therapeutic implications: interventions targeting sensory hypersensitivity and hyperarousal might yield benefits across a wide swath of behavioral comorbidities simultaneously, rather than requiring separate treatments for each condition.

The authors caution that their data are cross-sectional and clinic-based, drawn from children evaluated at specialty fragile X clinics and therefore not necessarily representative of the full population spectrum of the disorder, which includes individuals with milder presentations never referred to specialty care. Even so, the scale of the FORWARD database and the consistency of the findings give the profiles considerable weight. The research team suggests that the reported profiles of impairing behavioral comorbidities could assist clinicians in the early identification of behavioral symptoms in children with fragile X syndrome and in refining the management of those symptoms, and, they add, perhaps in other neurodevelopmental disorders as well, where multi-comorbidity burdens are similarly common and similarly under-characterized. The study was supported by cooperative agreements and a contract funded by the Centers for Disease Control and Prevention, and de-identified data from the FORWARD project are available under the project’s data sharing plan and CDC policies, opening the door for further analyses of how these behavioral trajectories unfold over time.

Subject of Research: Behavioral comorbidities and their co-occurrence patterns in children with fragile X syndrome

Article Title: Profile of Behavioral Comorbidities in Children With Fragile X Syndrome

Article References: Kaufmann, W. E., Horn, P. S., FORWARD Consortium, Berry-Kravis, E., Velinov, M., Talboy, A. L., Sherman, S. L., Kaufmann, W. E., Schuster, M., Tartaglia, N., Filipink, R. A., Budimirovic, D. B., Barbouth, D., Lightbody, A., Reiss, A., Delahunty, C. M., Hagerman, R. J., Hessl, D., Erickson, C. A., … Morris, S. M. (2026). Profile of Behavioral Comorbidities in Children With Fragile X Syndrome. Journal of Autism and Developmental Disorders. https://doi.org/10.1007/s10803-026-07525-8

Image Credits: AI Generated

DOI: 10.1007/s10803-026-07525-8

Keywords: fragile X syndrome, behavioral comorbidities, anxiety, attention problems, autism spectrum disorder, sensory problems, FORWARD registry, intellectual disability, hyperactivity, self-injurious behavior, neurodevelopmental disorders, FMR1