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Hereditary ataxias, especially when presenting sporadically in adulthood, present a particular diagnostic challenge owing to their great clinical and genetic heterogeneity. Currently, up to 75% of such patients remain without a genetic diagnosis. In an era of emerging disease‐modifying gene‐stratified therapies, the identification of causative alleles has become increasingly important. Over the past few years, the implementation of advanced bioinformatics tools and long‐read sequencing has allowed the identification of a number of novel repeat expansion disorders, such as the recently described spinocerebellar ataxia 27B (SCA27B) caused by a (GAA)•(TTC) repeat expansion in intron 1 of the fibroblast growth factor 14 (FGF14) gene. SCA27B is rapidly gaining recognition as one of the most common forms of adult‐onset hereditary ataxia, with several studies showing that it accounts for a substantial number (9–61%) of previously undiagnosed cases from different cohorts. First natural history studies and multiple reports have already outlined the progression and core phenotype of this novel disease, which consists of a late‐onset slowly progressive pan‐cerebellar syndrome that is frequently associated with cerebellar oculomotor signs, such as downbeat nystagmus, and episodic symptoms. Furthermore, preliminary studies in patients with SCA27B have shown promising symptomatic benefits of 4‐aminopyridine, an already marketed drug. This review describes the current knowledge of the genetic and molecular basis, epidemiology, clinical features and prospective treatment strategies in SCA27B. Spinocerebellar ataxia 27B is caused by a (GAA)•(TTC) repeat expansion in intron 1 of FGF14 and is a common cause of adult‐onset ataxia, accounting for 9–61% of previously undiagnosed cases in different ethnically diverse cohorts. The core phenotype consists of a late‐onset slowly progressive pan‐cerebellar syndrome with frequent oculomotor signs. Episodic symptoms, visual disturbances and downbeat nystagmus are commonly observed in patients with SCA27B. 4‐Aminopyridine is a promising symptomatic treatment.

Objectives The cause of downbeat nystagmus (DBN) remains unknown in a substantial number of patients (“idiopathic”), although intronic GAA expansions in FGF14 have recently been shown to account for almost 50% of yet idiopathic cases. Here, we hypothesized that biallelic RFC1 expansions may also represent a recurrent cause of DBN syndrome. Methods We genotyped the RFC1 repeat and performed in-depth phenotyping in 203 patients with DBN, including 65 patients with idiopathic DBN, 102 patients carrying an FGF14 GAA expansion, and 36 patients with presumed secondary DBN. Results Biallelic RFC1 AAGGG expansions were identified in 15/65 patients with idiopathic DBN (23%). None of the 102 GAA- FGF14 -positive patients, but 2/36 (6%) of patients with presumed secondary DBN carried biallelic RFC1 expansions. The DBN syndrome in RFC1 -positive patients was characterized by additional cerebellar impairment in 100% (15/15), bilateral vestibulopathy (BVP) in 100% (15/15), and polyneuropathy in 80% (12/15) of cases. Compared to GAA- FGF14 -positive and genetically unexplained patients, RFC1 -positive patients had significantly more frequent neuropathic features on examination and BVP. Furthermore, vestibular function, as measured by the video head impulse test, was significantly more impaired in RFC1 -positive patients. Discussion Biallelic RFC1 expansions are a common monogenic cause of DBN syndrome.

Background Whether spinocerebellar ataxia 27B (SCA27B) may present as a cerebellar multiple system atrophy (MSA-C) mimic remains undetermined. Objectives To assess the prevalence of FGF14 (GAA) ≥250 expansions in patients with MSA-C, to compare SCA27B and MSA-C clinical presentation and natural history. Methods FGF14 expansion screening combined with longitudinal deep-phenotyping in a prospective cohort of 195 patients with sporadic late-onset cerebellar ataxia. Results After a mean disease duration of 6.4 years, 111 patients were not meeting criteria for MSA-C while 24 and 60 patients had a final diagnosis of possible and probable MSA-C, respectively. 16 patients carried an FGF14 (GAA) ≥250 expansion in the group not meeting MSA-C criteria (14.4%), 3 patients in the possible MSA-C group (12.5%), but none among probable MSA-C cases. SCA27B patients were evolving more slowly than probable MSA-C patients. Conclusions FGF14 (GAA) ≥250 expansion may account for MSA look-alike cases and should be screened among slow progressors.

Background Autosomal-dominant spinocerebellar ataxia (ADCA) due to intronic GAA repeat expansion in FGF14 (SCA27B) is a recent, relatively common form of late-onset ataxia. Objective Here, we aimed to: (1) investigate the relative frequency of SCA27B in different clinically defined disease subgroups with late-onset ataxia collected among 16 tertiary Italian centers; (2) characterize phenotype and diagnostic findings of patients with SCA27B; (3) compare the Italian cohort with other cohorts reported in recent studies. Methods We screened 396 clinically diagnosed late-onset cerebellar ataxias of unknown cause, subdivided in sporadic cerebellar ataxia, ADCA, and multisystem atrophy cerebellar type. We identified 72 new genetically defined subjects with SCA27B. Then, we analyzed the clinical, neurophysiological, and imaging features of 64 symptomatic cases. Results In our cohort, the prevalence of SCA27B was 13.4% (53/396) with as high as 38.5% (22/57) in ADCA. The median age of onset of SCA27B patients was 62 years. All symptomatic individuals showed evidence of impaired balance and gait; cerebellar ocular motor signs were also frequent. Episodic manifestations at onset occurred in 31% of patients. Extrapyramidal features (17%) and cognitive impairment (25%) were also reported. Brain magnetic resonance imaging showed cerebellar atrophy in most cases (78%). Pseudo-longitudinal assessments indicated slow progression of ataxia and minimal functional impairment. Conclusion Patients with SCA27B in Italy present as an adult-onset, slowly progressive cerebellar ataxia with predominant axial involvement and frequent cerebellar ocular motor signs. The high consistency of clinical features in SCA27B cohorts in multiple populations paves the way toward large-scale, multicenter studies.

Clustering of voltage-gated sodium channels (VGSCs) within the neuronal axon initial segment (AIS) is critical for efficient action potential initiation. Although initially inserted into both somatodendritic and axonal membranes, VGSCs are concentrated within the axon through mechanisms that include preferential axonal targeting and selective somatodendritic endocytosis. How the endocytic machinery specifically targets somatic VGSCs is unknown. Here, using knockdown strategies, we show that noncanonical FGF13 binds directly to VGSCs in hippocampal neurons to limit their somatodendritic surface expression, although exerting little effect on VGSCs within the AIS. In contrast, homologous FGF14, which is highly concentrated in the proximal axon, binds directly to VGSCs to promote their axonal localization. Single-point mutations in FGF13 or FGF14 abrogating VGSC interaction in vitro cannot support these specific functions in neurons. Thus, our data showhow the concerted actions of FGF13 and FGF14 regulate the polarized localization of VGSCs that supports efficient action potential initiation.

Background This study aimed to investigate the prevalence, characteristics, and determinants of peripheral neuropathy in a large cohort of patients affected by spinocerebellar ataxia type 27B (SCA27B), a late‐onset cerebellar ataxia caused by heterozygous GAA repeat expansions in the first intron of the FGF14 gene. Methods A retrospective, multicenter study in which medical records of SCA27B patients diagnosed between January 2023 and July 2024 in 21 French ataxia/neurogenetic centers were reviewed. Those who had undergone electrodiagnostic study were included. Results Among 332 SCA27B patients, 170 had undergone an electrodiagnostic study and were included. Forty‐two (25%) were diagnosed with neuropathy: 16 with length‐dependent axonal sensorimotor neuropathy, 24 with length‐dependent axonal sensory neuropathy, one with sensory, and one with motor neuronopathy. Neuropathy was associated with male sex, older age at electrodiagnostic study, and risk factors for neuropathy but not with GAA expansion sizes. Patients with neuropathy had more severe disability at the last visit (median SARA score 12 vs. 8, p = 0.0024). Conclusions The prevalence of neuropathy in SCA27B patients was similar to that reported in the elderly general population. Neuropathies were predominantly non‐specific length‐dependent axonal neuropathies, primarily driven by aging and known risk factors rather than the underlying genetic abnormality.

Background Spinocerebellar ataxia 27B is the most common genetic late onset cerebellar ataxia (LOCA). However, it commonly overlaps with other genetic LOCA as with the cerebellar form of multiple system atrophy (MSA-C). Objectives To pinpoint which clinical signs and symptoms best discriminate between FGF14  + from FGF14  − patients at symptoms’ onset. Methods Twenty SCA27B (≥ 250 GAA repeat expansion) patients were retrospectively matched by gender and age at disease onset with 20 negative FGF14 (−) LOCA patients and with 20 MSA-C patients. Clinical features were ranked based on their contribution towards distinguishing between the groups (feature importance ranking). Results SCA27B patients had significantly higher rates of episodic symptoms, cerebellar oculomotor signs, dysdiadochokinesia, and alcohol intolerance than LOCA- FGF14  − ataxia patients. The lack of autonomic symptoms and MRI signs in SCA27B patients were the most discriminating features from MSA-C. An AUC of 0.87 was obtained if using the “top 3 clinical features model” (episodic symptoms, cerebellar oculomotor signs and dysdiadochokinesia) to distinguish SCAB27 from LCOA FGF14  − . Regarding MRI findings, no significant differences were found between SCA27B and FGF14  − patients, while a positive hot cross buns sign and the presence of brainstem atrophy were key distinguishing features between SCA27B from MSA-C patients ( p  < 0.005). Conclusion Our pilot case–control study contributes to the identification of early clinical symptoms to differentiate SCA27B to LOCA patients including FGF14 - and MSA-C ones. From a feature perspective, while clinical features are crucial, identifying surrogate biomarkers—such as ocular or gait parameters—could aid in the early diagnosis and follow-up of SCA27B patients.

Background and Purpose Multiple system atrophy (MSA) is a progressive, adult‐onset neurodegenerative disorder clinically characterized by combinations of autonomic failure, parkinsonism, cerebellar ataxia and pyramidal signs. Although a few genetic factors have been reported to contribute to the disease, its mutational profiles have not been systemically studied. Methods To address the genetic profiles of clinically diagnosed MSA patients, exome sequencing and triplet repeat detection was conducted in 205 MSA patients, including one familial case. The pathogenicity of variants was determined according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines. Results In the familial patient, a novel heterozygous COQ2 pathogenic variant (p.Ala351Thr) was identified in the MSA pedigree. In the sporadic patients, 29 pathogenic variants were revealed in 21 genes, and the PARK7 p.Ala104Thr variant was significantly associated with MSA (p = 0.0018). Moreover, burden tests demonstrated that the pathogenic variants were enriched in cerebellar ataxia‐related genes in patients. Furthermore, repeat expansion analyses revealed that two patients carried the pathogenic CAG repeat expansion in the CACNA1A gene (SCA6), one patient carried the (ACAGG)exp/(ACAGG)exp expansion in RFC1 and one carried the GAA‐pure expansion in FGF14 gene. Conclusion In conclusion, a novel COQ2 pathogenic variant was identified in a familial MSA patient, and repeat expansions in CACNA1A, RFC1 and FGF14 gene were detected in four sporadic patients. Moreover, a PARK7 variant and the burden of pathogenic variants in cerebellar ataxia‐related genes were associated with MSA.

We identified that Fibroblast Growth Factor 14 (FGF14) was preferentially methylated in colorectal cancer (CRC). In this study, we aimed to investigate the epigenetic regulation, biological function and molecular mechanism of FGF14 in CRC. The expression of FGF14 in CRC cell lines, normal human colon epithelial cell line, CRC tissues and paired adjacent normal tissues was detected by PCR and Western blot. The biological function of FGF14 in CRC was interrogated by cell viability assay, colony formation, flow cytometry, cell invasion and migration assay, as well as study. We found FGF14 was downregulated or silenced in all (10/10) CRC cell lines, while it was expressed in normal colonic tissues and normal human colon epithelial cell line. The expression of FGF14 was lower in primary CRCs as compared to their adjacent normal tissues. Significant higher methylation of FGF14 was observed in CRCs than that in normal tissues based on the data from TCGA database. The loss of FGF14 gene expression was restored by treatment with DNA methyltransferase inhibitor 5-Aza. Re-expression of FGF14 in CRC cell lines inhibited cell viability and colony formation, and induced cell apoptosis. FGF14 induced mitochondrial apoptosis and inhibited PI3K/AKT/mTOR pathway. In xenograft mouse model, overexpression of FGF14 significantly reduced tumor growth ( <0.001). In conclusion, FGF14 is a novel tumor suppressor, which suppresses cell proliferation and induces cell apoptosis mediating PI3K/AKT/mTOR pathway.

BackgroundThe ethnic diversity of India provides a unique opportunity to study the history of the origin of mutations of genetic disorders. Spinocerebellar ataxia type 27B (SCA27B), a recently identified dominantly inherited cerebellar disorder is caused by GAA-repeat expansions in intron 1 of Fibroblast Growth Factor 14 (FGF14). Predominantly reported in the European population, we aimed to screen this mutation and study the founder haplotype of SCA27B in Indian ataxia patients.MethodsWe have undertaken screening of GAA repeats in a large Indian cohort of ~ 1400 uncharacterised ataxia patients and kindreds and long-read sequencing-based GAA repeat length assessment. High throughput genotyping-based haplotype analysis was also performed. We utilized ~ 1000 Indian genomes to study the GAA at-risk expansion alleles.FindingsWe report a high frequency of 1.83% (n = 23) of SCA27B in the uncharacterized Indian ataxia cohort. We observed several biallelic GAA expansion mutations (n = 5) with younger disease onset. We observed a risk haplotype (AATCCGTGG) flanking the FGF14-GAA locus over a 74 kb region in linkage disequilibrium. We further studied the frequency of this risk haplotype across diverse geographical population groups. The highest prevalence of the risk haplotype was observed in the European population (29.9%) followed by Indians (21.5%). The observed risk haplotype has existed through ~ 1100 generations (~ 22,000 years), assuming a correlated genealogy.InterpretationThis study provides valuable insights into SCA27B and its Upper Paleolithic origin in the Indian subcontinent. The high occurrence of biallelic expansion is probably relevant to the endogamous nature of the Indian population.