The genetic basis of early-onset hereditary ataxia in Iran: results of a national registry of a heterogeneous population.

BACKGROUND: To investigate the genetics of early-onset progressive cerebellar ataxia in Iran, we conducted a study at the Children's Medical Center (CMC), the primary referral center for pediatric disorders in the country, over a three-year period from 2019 to 2022. In this report, we provide the initial findings from the national registry. METHODS: We selected all early-onset patients with an autosomal recessive mode of inheritance to assess their phenotype, paraclinical tests, and genotypes. The clinical data encompassed clinical features, the Scale for the Assessment and Rating of Ataxia (SARA) scores, Magnetic Resonance Imaging (MRI) results, Electrodiagnostic exams (EDX), and biomarker features. Our genetic investigations included single-gene testing, Whole Exome Sequencing (WES), and Whole Genome Sequencing (WGS). RESULTS: Our study enrolled 162 patients from various geographic regions of our country. Among our subpopulations, we identified known and novel pathogenic variants in 42 genes in 97 families. The overall genetic diagnostic rate was 59.9%. Notably, we observed PLA2G6, ATM, SACS, and SCA variants in 19, 14, 12, and 10 families, respectively. Remarkably, more than 59% of the cases were attributed to pathogenic variants in these genes. CONCLUSIONS: Iran, being at the crossroad of the Middle East, exhibits a highly diverse genetic etiology for autosomal recessive hereditary ataxia. In light of this heterogeneity, the development of preventive strategies and targeted molecular therapeutics becomes crucial. A national guideline for the diagnosis and management of patients with these conditions could significantly aid in advancing healthcare approaches and improving patient outcomes.

[Recent clinical advances in hereditary spinocerebellar degeneration].

Spinocerebellar degeneration (SCD) is a neurodegenerative disorder characterized by cerebellar ataxia and other multisystem manifestations, such as Parkinsonism and pyramidal tract symptoms. No effective treatment is available for SCD. Approximately one-third of the cases of SCD are inherited, and the remaining two-third are sporadic, including multiple system atrophy. This article provides an overview of hereditary SCD, its clinical features, recent treatment advances, biomarkers, role of genomic medicine, and future treatment prospects.

The FGF14 GAA repeat expansion in Greek patients with late-onset cerebellar ataxia and an overview of the SCA27B phenotype across populations.

A pathogenic GAA repeat expansion in the first intron of the fibroblast growth factor 14 gene (FGF14) has been recently identified as the cause of spinocerebellar ataxia 27B (SCA27B). We herein screened 160 Greek index cases with late-onset cerebellar ataxia (LOCA) for FGF14 repeat expansions using a combination of long-range PCR and bidirectional repeat-primed PCRs. We identified 19 index cases (12%) carrying a pathogenic FGF14 GAA expansion, a diagnostic yield higher than that of previously screened repeat-expansion ataxias in Greek LOCA patients. The age at onset of SCA27B patients was 60.5 ± 12.3 years (range, 34-80). Episodic onset (37%), downbeat nystagmus (32%) and vertigo (26%) were significantly more frequent in FGF14 expansion-positive cases compared to expansion-negative cases. Beyond typical cerebellar signs, SCA27B patients often displayed hyperreflexia (47%) and reduced vibration sense in the lower extremities (42%). The frequency and phenotypic profile of SCA27B in Greek patients was similar to most other previously studied populations. We conclude that FGF14 GAA repeat expansions are the commonest known genetic cause of LOCA in the Greek population and recommend prioritizing testing for FGF14 expansions in the diagnostic algorithm of patients with LOCA.

A Review of Ocular Movement Abnormalities in Hereditary Cerebellar Ataxias.

Cerebellar ataxias are a wide heterogeneous group of disorders that may present with fine motor deficits as well as gait and balance disturbances that have a significant influence on everyday activities. To review the ocular movements in cerebellar ataxias in order to improve the clinical knowledge of cerebellar ataxias and related subtypes. English papers published from January 1990 to May 2022 were selected by searching PubMed services. The main search keywords were ocular motor, oculomotor, eye movement, eye motility, and ocular motility, along with each ataxia subtype. The eligible papers were analyzed for clinical presentation, involved mutations, the underlying pathology, and ocular movement alterations. Forty-three subtypes of spinocerebellar ataxias and a number of autosomal dominant and autosomal recessive ataxias were discussed in terms of pathology, clinical manifestations, involved mutations, and with a focus on the ocular abnormalities. A flowchart has been made using ocular movement manifestations to differentiate different ataxia subtypes. And underlying pathology of each subtype is reviewed in form of illustrated models to reach a better understanding of each disorder.

Prevalence of repeat expansions causing autosomal dominant spinocerebellar ataxias in Hokkaido, the northernmost island of Japan.

In Japan, approximately 30% of spinocerebellar degeneration (SCD) is hereditary, and more than 90% of hereditary SCD is autosomal dominant SCD (AD-SCD). We have previously reported the types of AD-SCD in Hokkaido, twice. In this study, we investigated the status of AD-SCD mainly due to repeat expansions, covering the period since the last report. We performed genetic analysis for 312 patients with a clinical diagnosis of SCD, except for multiple system atrophy at medical institutions in Hokkaido between January 2007 and December 2020. The median age at the time of analysis was 58 (1-86) years. Pathogenic variants causing AD-SCD due to repeat expansion were found in 61.5% (192 cases). Spinocerebellar ataxia (SCA) 6 was the most common type in 25.3% (79 cases), followed by Machado-Joseph disease (MJD)/SCA3 in 13.8% (43), SCA1 in 6.4% (20), SCA2 in 5.1% (16), SCA31 in 4.8% (15), dentatorubral-pallidoluysian atrophy in 4.8% (15), SCA7 in 0.6% (2), and SCA8 in 0.6% (2). SCA17, 27B, 36, and 37 were not found. Compared to previous reports, this study found a higher prevalence of SCA6 and a lower prevalence of MJD/SCA3. An increasing number of cases identified by genetic testing, including cases with no apparent family history, accurately revealed the distribution of disease types in Hokkaido.

Spinocerebellar ataxia type 11 (SCA11): TTBK2 variants, functions and associated disease mechanisms.

Spinocerebellar ataxia type 11 (SCA11) is a rare type of autosomal dominant cerebellar ataxia, mainly characterized by progressive cerebellar ataxia, abnormal eye signs and dysarthria. SCA11 is caused by variants in TTBK2, which encodes tau tubulin kinase 2 (TTBK2) protein. Only a few families with SCA11 were described to date, all harbouring small deletions or insertions that result in frameshifts and truncated TTBK2 proteins. In addition, TTBK2 missense variants were also reported but they were either benign or still needed functional validation to ascertain their pathogenic potential in SCA11. The mechanisms behind cerebellar neurodegeneration mediated by TTBK2 pathogenic alleles are not clearly established. There is only one neuropathological report and a few functional studies in cell or animal models published to date. Moreover, it is still unclear whether the disease is caused by TTBK2 haploinsufficiency of by a dominant negative effect of TTBK2 truncated forms on the normal allele. Some studies point to a lack of kinase activity and mislocalization of mutated TTBK2, while others reported a disruption of normal TTBK2 function caused by SCA11 alleles, particularly during ciliogenesis. Although TTBK2 has a proven function in cilia formation, the phenotype caused by heterozygous TTBK2 truncating variants are not clearly typical of ciliopathies. Thus, other cellular mechanisms may explain the phenotype seen in SCA11. Neurotoxicity caused by impaired TTBK2 kinase activity against known neuronal targets, such as tau, TDP-43, neurotransmitter receptors or transporters, may contribute to neurodegeneration in SCA11.

Exonic trinucleotide repeat expansions in ZFHX3 cause spinocerebellar ataxia type 4: A poly-glycine disease.

Autosomal-dominant ataxia with sensory and autonomic neuropathy is a highly specific combined phenotype that we described in two Swedish kindreds in 2014; its genetic cause had remained unknown. Here, we report the discovery of exonic GGC trinucleotide repeat expansions, encoding poly-glycine, in zinc finger homeobox 3 (ZFHX3) in these families. The expansions were identified in whole-genome datasets within genomic segments that all affected family members shared. Non-expanded alleles carried one or more interruptions within the repeat. We also found ZFHX3 repeat expansions in three additional families, all from the region of Skåne in southern Sweden. Individuals with expanded repeats developed balance and gait disturbances at 15 to 60 years of age and had sensory neuropathy and slow saccades. Anticipation was observed in all families and correlated with different repeat lengths determined through long-read sequencing in two family members. The most severely affected individuals had marked autonomic dysfunction, with severe orthostatism as the most disabling clinical feature. Neuropathology revealed p62-positive intracytoplasmic and intranuclear inclusions in neurons of the central and enteric nervous system, as well as alpha-synuclein positivity. ZFHX3 is located within the 16q22 locus, to which spinocerebellar ataxia type 4 (SCA4) repeatedly had been mapped; the clinical phenotype in our families corresponded well with the unique phenotype described in SCA4, and the original SCA4 kindred originated from Sweden. ZFHX3 has known functions in neuronal development and differentiation n both the central and peripheral nervous system. Our findings demonstrate that SCA4 is caused by repeat expansions in ZFHX3.

Clinical variability associated with intronic FGF14 GAA repeat expansion in Japan.

BACKGROUND AND OBJECTIVES: The GAA repeat expansion within the fibroblast growth factor 14 (FGF14) gene has been found to be associated with late-onset cerebellar ataxia. This study aimed to investigate the genetic causes of cerebellar ataxia in patients in Japan. METHODS: We collected a case series of 940 index patients who presented with chronic cerebellar ataxia and remained genetically undiagnosed after our preliminary genetic screening. To investigate the FGF14 repeat locus, we employed an integrated diagnostic strategy that involved fluorescence amplicon length analysis polymerase chain reaction (PCR), repeat-primed PCR, and long-read sequencing. RESULTS: Pathogenic FGF14 GAA repeat expansions were detected in 12 patients from 11 unrelated families. The median size of the pathogenic GAA repeat was 309 repeats (range: 270-316 repeats). In these patients, the mean age of onset was 66.9 ± 9.6 years, with episodic symptoms observed in 56% of patients and parkinsonism in 30% of patients. We also detected FGF14 repeat expansions in a patient with a phenotype of multiple system atrophy, including cerebellar ataxia, parkinsonism, autonomic ataxia, and bilateral vocal cord paralysis. Brain magnetic resonance imaging (MRI) showed normal to mild cerebellar atrophy, and a follow-up study conducted after a mean period of 6 years did not reveal any significant progression. DISCUSSION: This study highlights the importance of FGF14 GAA repeat analysis in patients with late-onset cerebellar ataxia, particularly when they exhibit episodic symptoms, or their brain MRI shows no apparent cerebellar atrophy. Our findings contribute to a better understanding of the clinical variability of GAA-FGF14-related diseases.

A Novel Pathogenic Variant in the SCA25-Related Gene Expanding the Etiology of Early-Onset and Progressive Cerebellar Ataxia in Childhood.

Spinocerebellar ataxias (SCAs) are heterogeneous autosomal dominant progressive ataxic disorders. SCA25 has been linked to PNPT1 pathogenic variants. Although pediatric onset is not unusual, to date only one patient with onset in the first years of life has been reported. This study presents an additional case, wherein symptoms emerged during the toddler phase, accompanied by the identification of a novel PNPT1 variant. The child was seen at 3 years because of frequent falls. Neurological examination revealed cerebellar signs and psychomotor delay. Brain MRI showed cerebellar atrophy (CA), cerebellar cortex, and dentate nuclei hyperintensities. Metabolic and genetic testing was inconclusive. At follow-up (age 6), the child had clinically and radiologically worsened; electroneurography (ENG) revealed axonal sensory neuropathy. Screening of genes associated with ataxias and mitochondrial disease identified a novel, heterozygous variant in PNPT1, which was probably pathogenic. This variant was also detected in the proband's mother and maternal grandmother, both asymptomatic, which aligns with the previously documented incomplete penetrance of heterozygous PNPT1 variants. Our study confirms that SCA25 can have onset in early childhood and characterizes natural history in pediatric cases: progressive cerebellar ataxia with sensory neuropathy, which manifests during the course of the disease. We report for the first time cerebellar gray matter hyperintensities, suggesting that SCA25 should be included in the differential diagnosis of cerebellar ataxias associated with such brain imaging features. In summary, SCA25 should be considered in the diagnostic workup of early onset pediatric progressive ataxias. Additionally, we confirm an incomplete penetrance and highly variable expressivity of PNPT1-associated SCA25.

A Novel c.3636-4 A>G Mutation in the CCDC88C Plays a Causative Role in Familial Spinocerebellar Ataxia.

INTRODUCTION: Spinocerebellar ataxia (SCA) is an autosomal dominant genetic disease characterized by cerebellar neurological deficits. Specifically, its primary clinical manifestation is ataxia accompanied by peripheral nerve damage. A total of 48 causative genes of SCA have been identified. This study aimed to identify causative genes of autosomal dominant SCA in a four-generation Chinese kindred comprising eight affected individuals. METHODS: Genomic DNA samples were extracted from the pedigree members, and genomic whole-exome sequencing was performed, followed by bidirectional Sanger sequencing, and minigene assays to identify mutation sites. RESULTS: A novel pathogenic heterozygous mutation in the splice region of the coiled-coil domain containing the 88C (CCDC88C) gene (NM_001080414:c.3636-4 A>G) was identified in four affected members. The minigene assay results indicated that this mutation leads to the insertion of CAG bases (c.3636-1_3636-3 insCAG). CONCLUSION: CCDC88C gene mutation leads to SCA40 (OMIM:616053), which is a rare subtype of SCA without symptoms during childhood. Our findings further demonstrated the role of the CCDC88C gene in SCA and indicated that the c.3636-4 A>G (NM_001080414) variant of CCDC88C is causative for a later-onset phenotype of SCA40. Our findings enrich the mutation spectrum of CCDC88C gene and provide a theoretical basis for the genetic counseling of SCA40.

Pure cerebellar ataxia due to bi-allelic PRDX3 variants including recurring p.Asp202Asn.

Bi-allelic variants in peroxiredoxin 3 (PRDX3) have only recently been associated with autosomal recessive spinocerebellar ataxia characterized by early onset slowly progressive cerebellar ataxia, variably associated with hyperkinetic and hypokinetic features, accompanied by cerebellar atrophy and occasional olivary and brainstem involvement. Herein, we describe a further simplex case carrying a reported PRDX3 variant as well as two additional cases with novel variants. We report the first Brazilian patient with SCAR32, replicating the pathogenic status of a known variant. All presented cases from the Brazilian and Indian populations expand the phenotypic spectrum of the disease by displaying prominent neuroradiological findings. SCAR32, although rare, should be included in the differential diagnosis of sporadic or recessive childhood and adolescent-onset pure and complex cerebellar ataxia.

Coexistence of multiple sclerosis and spinocerebellar ataxia type-8.

Cerebellar dysfunction is likely to cause severe and treatment-resistant disability in multiple sclerosis (MS). Certain spinocerebellar ataxia (SCA)-related alleles can increase MS susceptibility, and channel polymorphisms can impact disability measures. Following an index patient with the coexistence of MS and SCA Type-8 (SCA8) in the MS clinic, an institutional engine search for MS and hereditary ataxia coexistence was conducted but did not reveal any other cases. This extremely rare coexistence of MS and SCA8 in our index patient may be incidental; however, a yet-to-be-identified contribution of coexistent hereditary ataxia(s) to the susceptibility of a prominent progressive ataxia MS phenotype cannot be ruled out.

Natural History and Phenotypic Spectrum of GAA-FGF14 Sporadic Late-Onset Cerebellar Ataxia (SCA27B).

BACKGROUND: Heterozygous GAA expansions in the FGF14 gene have been related to autosomal dominant cerebellar ataxia (SCA27B-MIM:620174). Whether they represent a common cause of sporadic late-onset cerebellar ataxia (SLOCA) remains to be established. OBJECTIVES: To estimate the prevalence, characterize the phenotypic spectrum, identify discriminative features, and model longitudinal progression of SCA27B in a prospective cohort of SLOCA patients. METHODS: FGF14 expansions screening combined with longitudinal deep-phenotyping in a prospective cohort of 118 SLOCA patients (onset >40 years of age, no family history of cerebellar ataxia) without a definite diagnosis. RESULTS: Prevalence of SCA27B was 12.7% (15/118). Higher age of onset, higher Spinocerebellar Degeneration Functional Score, presence of vertigo, diplopia, nystagmus, orthostatic hypotension absence, and sensorimotor neuropathy were significantly associated with SCA27B. Ataxia progression was ≈0.4 points per year on the Scale for Assessment and Rating of Ataxia. CONCLUSIONS: FGF14 expansion is a major cause of SLOCA. Our natural history data will inform future FGF14 clinical trials. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

An E280K Missense Variant in KCND3/Kv4.3-Case Report and Functional Characterization.

A five-year-old girl presented with headache attacks, clumsiness, and a history of transient gait disturbances. She and her father, mother, twin sister, and brother underwent neurological evaluation, neuroimaging, and exome sequencing covering 357 genes associated with movement disorders. Sequencing revealed the new variant KCND3 c.838G>A, p.E280K in the father and sisters, but not in the mother and brother. KCND3 encodes voltage-gated potassium channel D3 (Kv4.3) and mutations have been associated with spinocerebellar ataxia type 19/22 (SCA19/22) and cardiac arrhythmias. SCA19/22 is characterized by ataxia, Parkinsonism, peripheral neuropathy, and sometimes, intellectual disability. Neuroimaging, EEG, and ECG were unremarkable. Mild developmental delay with impaired fluid reasoning was observed in both sisters, but not in the brother. None of the family members demonstrated ataxia or parkinsonism. In Xenopus oocyte electrophysiology experiments, E280K was associated with a rightward shift in the Kv4.3 voltage-activation relationship of 11 mV for WT/E280K and +17 mV for E280K/E280K relative to WT/WT. Steady-state inactivation was similarly right-shifted. Maximal peak current amplitudes were similar for WT/WT, WT/E280K, and E280K/E280K. Our data indicate that Kv4.3 E280K affects channel activation and inactivation and is associated with developmental delay. However, E280K appears to be relatively benign considering it does not result in overt ataxia.

Spinocerebellar ataxia type 8 presents as progressive supranuclear palsy.

Spinocerebellar ataxia type 8 is a progressive neurodegenerative disease induced by expansion of CTA/CTG repeats in an untranslated region of the ATXN8/ATXN8OS gene. We report an elderly female patient presenting with rigidity, bradykinesia, ataxia and oculomotor defect at the disease onset age of 65 years old without family history, and hummingbird sign in cranial MRI, initially diagnosed as progressive supranuclear palsy (PSP). But genetic test showed that one allele of ATXN8OS gene had more than 131 CTA/CTG repeats which was a full penetrance mutant. It's possible that this is a case of PSP with an ATXN8OS gene mutation that doesn't contribute to the phenotype. Whether the ATXN8OS gene CTA/CTG repeats cause PSP phenotype needs further investigation with larger samples and pathological findings.

Spinocerebellar ataxia type 11 (SCA11): An update.

Spinocerebellar ataxias, also called autosomal dominant cerebellar ataxias, are a group of neurological genetic diseases characterised by chronic, progressive cerebellar ataxia. The clinical hallmark of spinocerebellar ataxia is the loss of balance and coordination, accompanied by slurred speech. Spinocerebellar ataxia type 11 is a rare subtype of spinocerebellar ataxia caused by mutations in the tau tubulin kinase 2 gene. Patients with spinocerebellar ataxia are clinically characterised by slowly progressive cerebellar ataxia, trunk and limb ataxia, and eye movement abnormalities with occasional pyramidal features. Peripheral neuropathy and dystonia are rare. According to the literature, only nine families affected with spinocerebellar ataxia have been reported worldwide. Herein, a series of spinocerebellar ataxia cases are discussed in detail to determine the potential research direction of this dysfunction, including its epidemiology, clinical features, genetic characteristics, diagnosis and differential diagnosis, pathogenic mechanisms, treatment, prognosis, follow-up, genetic counselling and future perspectives, and to improve the overall understanding of spinocerebellar ataxia among clinicians, researchers and patients.

Phenotypic and genetic aspects of hereditary ataxia in dogs.

Hereditary ataxias are a large group of neurodegenerative diseases that have cerebellar or spinocerebellar dysfunction as core feature, occurring as an isolated sign or as part of a syndrome. Based on neuropathology, this group of diseases has so far been classified into cerebellar cortical degenerations, spinocerebellar degenerations, cerebellar ataxias without substantial neurodegeneration, canine multiple system degeneration, and episodic ataxia. Several new hereditary ataxia syndromes are described, but most of these diseases have similar clinical signs and unspecific diagnostic findings, wherefore achieving a definitive diagnosis in these dogs is challenging. Eighteen new genetic variants associated with these diseases have been discovered in the last decade, allowing clinicians to reach a definitive diagnosis for most of these conditions, and allowing breeding schemes to adapt to prevent breeding of affected puppies. This review summarizes the current knowledge about hereditary ataxias in dogs, and proposes to add a "multifocal degenerations with predominant (spino)cerebellar component" category regrouping canine multiple system degeneration, new hereditary ataxia syndromes that do not fit in 1 of the previous categories, as well as specific neuroaxonal dystrophies and lysosomal storage diseases that cause major (spino)cerebellar dysfunction.

Gene Suppression Therapies in Hereditary Cerebellar Ataxias: A Systematic Review of Animal Studies.

INTRODUCTION: Hereditary cerebellar ataxias (HCAs) are a heterogenous group of neurodegenerative disorders associated with severe disability. Treatment options are limited and overall restricted to symptomatic approaches, leading to poor prognoses. In recent years, there has been extensive research on gene suppression therapies (GSTs) as a new hope for disease-modifying strategies. In this article, we aim to perform a review of in vivo studies investigating the efficacy and safety profile of GSTs in HCAs. METHODS: A structured PubMed® search on GSTs in HCAs from January 1993 up to October 2020 was performed. Inclusion and exclusion criteria were defined, and the selection process was conducted accordingly. The screening process was independently carried out by two authors and was initially based on title and abstract, followed by full-text reading. The risk-of-bias assessment was performed with SYRCLE's tool. A data extraction sheet was created to collect relevant information from each selected article. RESULTS: The initial search yielded 262 papers, of which 239 were excluded. An additional article was obtained following reference scrutiny, resulting in a total of 24 articles for final analysis. Most studies were not clear on the tools used to assess bias. In SCA1, SCA2, MJD/SCA3 and SCA7, RNA interference (iRNA) and antisense oligonucleotide (ASO) therapies proved to be well tolerated and effective in suppressing mutant proteins, improving neuropathological features and the motor phenotype. In SCA6, the phenotype was improved, but no investigation of adverse effects was performed. In FRDA, only the suppression efficacy of the electroporation of the clustered regularly interspaced short palindromic repeats associated with Cas9 enzyme system (CRISPR-Cas9) system was tested and confirmed. CONCLUSION: The literature reviewed suggests that GSTs are well tolerated and effective in suppressing the targeted proteins, improving neuropathological features and the motor phenotype in vivo. Nonetheless, there is no guarantee that these results are free of bias. Moreover, further investigation is still needed to clarify the GST effect on HCAs such as FRDA, SCA6 and SCA2.

Spinocerebellar Ataxia in a Hungarian Female Patient with a Novel Variant of Unknown Significance in the CCDC88C Gene.

Spinocerebellar ataxia (SCA) 40 is an extremely rare subtype of the phenotypically and genetically diverse autosomal dominant ataxias caused by mutations of the CCDC88C gene. Most reported cases of SCA40 are characterized by late-onset cerebellar ataxia and variable extrapyramidal features; however, there is a report of a patient with early-onset spastic paraparesis as well. Here, we describe a novel missense CCDC88C mutation (p.R203W) in the hook domain of the DAPLE protein encoded by the CCDC88C gene that was identified in a female patient who developed late-onset ataxia, dysmetria and intention tremor. To explore the molecular consequences of the newly identified and previously described CCDC88C mutations, we carried out in vitro functional tests. The CCDC88C alleles were expressed in HEK293 cells, and the impact of the mutant DAPLE protein variants on JNK pathway activation and apoptosis was assessed. Our results revealed only a small-scale activation of the JNK pathway by mutant DAPLE proteins; however, increased JNK1 phosphorylation could not be detected. Additionally, none of the examined mutations triggered proapoptotic effect. In conclusion, we identified a novel mutation of the CCDC88C gene from a patient with spinocerebellar ataxia. Our results are not in accord with previous observations and do not support the primary role of the CCDC88C mutations in induction of JNK pathway activation in ataxia. Therefore, we propose that CCDC88C mutations may exert their effects through different and possibly in much broader, yet unexplored, biological processes.

Functional genomics provide key insights to improve the diagnostic yield of hereditary ataxia.

Improvements in functional genomic annotation have led to a critical mass of neurogenetic discoveries. This is exemplified in hereditary ataxia, a heterogeneous group of disorders characterised by incoordination from cerebellar dysfunction. Associated pathogenic variants in more than 300 genes have been described, leading to a detailed genetic classification partitioned by age-of-onset. Despite these advances, up to 75% of patients with ataxia remain molecularly undiagnosed even following whole genome sequencing, as exemplified in the 100 000 Genomes Project. This study aimed to understand whether we can improve our knowledge of the genetic architecture of hereditary ataxia by leveraging functional genomic annotations, and as a result, generate insights and strategies that raise the diagnostic yield. To achieve these aims, we used publicly-available multi-omics data to generate 294 genic features, capturing information relating to a gene's structure, genetic variation, tissue-specific, cell-type-specific and temporal expression, as well as protein products of a gene. We studied these features across genes typically causing childhood-onset, adult-onset or both types of disease first individually, then collectively. This led to the generation of testable hypotheses which we investigated using whole genome sequencing data from up to 2182 individuals presenting with ataxia and 6658 non-neurological probands recruited in the 100 000 Genomes Project. Using this approach, we demonstrated a high short tandem repeat (STR) density within childhood-onset genes suggesting that we may be missing pathogenic repeat expansions within this cohort. This was verified in both childhood- and adult-onset ataxia patients from the 100 000 Genomes Project who were unexpectedly found to have a trend for higher repeat sizes even at naturally-occurring STRs within known ataxia genes, implying a role for STRs in pathogenesis. Using unsupervised analysis, we found significant similarities in genomic annotation across the gene panels, which suggested adult- and childhood-onset patients should be screened using a common diagnostic gene set. We tested this within the 100 000 Genomes Project by assessing the burden of pathogenic variants among childhood-onset genes in adult-onset patients and vice versa. This demonstrated a significantly higher burden of rare, potentially pathogenic variants in conventional childhood-onset genes among individuals with adult-onset ataxia. Our analysis has implications for the current clinical practice in genetic testing for hereditary ataxia. We suggest that the diagnostic rate for hereditary ataxia could be increased by removing the age-of-onset partition, and through a modified screening for repeat expansions in naturally-occurring STRs within known ataxia-associated genes, in effect treating these regions as candidate pathogenic loci.