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Background: Intracerebral hemorrhage (ICH) is the most devastating adverse outcome for patients on anticoagulants. Clinical risk scores that quantify bleeding risk can guide decision-making in situations when indication or duration for anticoagulation is uncertain. We investigated whether integration of a genetic risk score into an existing risk factor–based CRS could improve risk stratification for anticoagulation-related ICH. Methods: We constructed 153 genetic risk scores from genome-wide association data of 1545 ICH cases and 1481 controls and validated them in 431 ICH cases and 431 matched controls from the population-based UK Biobank. The score that explained the largest variance in ICH risk was selected and tested for prediction of incident ICH in an independent cohort of 5530 anticoagulant users. A CRS for major anticoagulation-related hemorrhage, based on 8/9 components of the HAS-BLED score, was compared with a combined clinical and genetic risk score incorporating an additional point for high genetic risk for ICH. Results: Among anticoagulated individuals, 94 ICH occurred over a mean follow-up of 11.9 years. Compared with the lowest genetic risk score tertile, being in the highest tertile was associated with a two-fold increased risk for incident ICH (hazard ratio, 2.08 [95% CI, 1.22–3.56]). Although the CRS predicted incident ICH with a hazard ratio of 1.24 per 1-point increase (95% CI [1.01–1.53]), adding a point for high genetic ICH risk led to a stronger association (hazard ratio of 1.33 per 1-point increase [95% CI, 1.11–1.59]) with improved risk stratification (C index 0.57 versus 0.53) and maintained calibration (integrated calibration index 0.001 for both). The new clinical and genetic risk score showed 19% improvement in high-risk classification among individuals with ICH and a net reclassification improvement of 0.10. Conclusions: Among anticoagulant users, a prediction score incorporating genomic information is superior to a clinical risk score alone for ICH risk stratification and could serve in clinical decision-making.

ObjectiveGenome-wide association studies have identified1q22as a susceptibility locus for cerebral small vessel diseases (CSVDs), including non-lobar intracerebral hemorrhage (ICH) and lacunar stroke. In the present study we performed targeted high-depth sequencing of1q22in ICH cases and controls to further characterize this locus and prioritize potential causal mechanisms, which remain unknown.Methods95,000 base pairs spanning1q22, includingSEMA4A, SLC25A44andPMF1/PMF1-BGLAPwere sequenced in 1,055 spontaneous ICH cases (534 lobar and 521 non-lobar) and 1,078 controls. Firth regression and RIFT analysis were used to analyze common and rare variants, respectively. Chromatin interaction analyses were performed using Hi-C, ChIP-Seq and ChIA-PET databases. Multivariable Mendelian randomization (MVMR) assessed whether alterations in gene-specific expression relative to regionally co-expressed genes at1q22could be causally related to ICH risk.ResultsCommon and rare variant analyses prioritized variants inSEMA4A5’-UTR andPMF1intronic regions, overlapping with active promoter and enhancer regions based on ENCODE annotation. Hi-C data analysis determined that1q22is spatially organized in a single chromatin loop and that the genes therein belong to the same Topologically Associating Domain. ChIP-Seq and ChIA-PET data analysis highlighted the presence of long-range interactions between theSEMA4A-promoter andPMF1-enhancer regions prioritized by association testing. MVMR analyses demonstrated thatPMF1overexpression could be causally related to non-lobar ICH risk.InterpretationAltered promoter-enhancer interactions leading toPMF1overexpression, potentially dysregulating polyamine catabolism, could explain demonstrated associations with non-lobar ICH risk at1q22, offering a potential new target for prevention of ICH and CSVD.

IntroductionWhile stroke education is a hallmark of clinical care in primary stroke centers, the educational attainment of patients is rarely considered. The objective of this study is to determine whether educational attainment, in addition to traditional risk factors, is associated with intracerebral hemorrhage (ICH) severity and functional outcomes.MethodsSubjects were enrolled in a prospectively ascertained cohort of patients with primary ICH from 1994 until 2020 at the Massachusetts General Hospital Neurosciences Intensive Care Unit. Data on social determinants of health (SDOH), past medical history for ICH risk factors, and ICH severity were obtained on admission. The primary outcome was stroke severity, calculated using the ICH score. The secondary outcome was 12-month modified Rankin Score (mRS).ResultsOf 2,539 patients eligible for analyses, 1,744 (69%) presented with mild ICH (ICH Score < 3) and 795 (31%) presented with severe ICH (ICH score ≥3). In a multivariable logistic regression analysis controlling for age, income, and a pre-stroke diagnosis of coronary artery disease, only educational attainment was associated with stroke severity, with patients with high school-only education more likely to present with a severe ICH compared to college diplomates (odds ratio 2.37, 95% CI 1.77, 3.19).Additionally, those with high school-only education were less likely to recover to a good functional outcome (mRSDiscussionPre-stroke educational attainment is an independent predictor of ICH severity and subsequent functional outcomes at 12-month post-stroke. Given the association with recovery, tailoring inpatient stroke education to level of educational attainment may serve to reduce the disparity in outcomes after hemorrhagic stroke. Educational attainment may act as both a social and a biological determinant, and could represent a modifiable risk factor for ICH survivors.

Valproate is a candidate for ischemic stroke prevention due to its anti-atherosclerotic effects in vivo. Although valproate use is associated with decreased ischemic stroke risk in observational studies, confounding by indication precludes causal conclusions. To overcome this limitation, we applied Mendelian randomization to determine whether genetic variants that influence seizure response among valproate users associate with ischemic stroke. We derived a genetic score for valproate response using genome-wide association data of seizure response after valproate intake from the Epilepsy Pharmacogenomics Consortium. We then tested this score among valproate users of the UK Biobank for association with incident and recurrent ischemic stroke using Cox proportional hazard models. Among 2,150 valproate users (mean 56 years, 54% females), 82 ischemic strokes occurred over a mean 12-year follow-up. Higher valproate response genetic score was associated with higher serum valproate levels (+5.78 mcg/ml per one SD, 95% CI [3.45, 8.11]). After adjusting for age and sex, higher valproate response genetic score was associated with lower ischemic stroke risk (HR per one SD 0.73, [0.58, 0.91]) with a halving of absolute risk in the highest compared to the lowest score tertile (4.8% vs 2.5%, p-trend=0.027). Among 194 valproate users with prevalent stroke at baseline, a higher valproate response genetic score was associated with lower recurrent ischemic stroke risk (HR per one SD 0.53, [0.32, 0.86]) with reduced absolute risk in the highest compared to the lowest score tertile (3/51, 5.9% vs. 13/71, 18.3%, p-trend=0.026). The valproate response genetic score was not associated with ischemic stroke among the 427,997 valproate non-users (p=0.61), suggesting minimal pleiotropy. In an independent cohort of 1,241 valproate users of the Mass General Brigham Biobank with 99 ischemic stroke events over 6.5 years follow-up, we replicated our observed associations between the valproate response genetic score and ischemic stroke (HR per one SD 0.77, 95% CI: [0.61, 0.97]). These results demonstrate that a genetically predicted favorable seizure response to valproate is associated with higher serum valproate levels and reduced ischemic stroke risk among valproate users, providing causal support for valproate effectiveness in ischemic stroke prevention. The strongest effect was found for recurrent ischemic stroke, suggesting potential dual-use benefits of valproate for post-stroke epilepsy. Clinical trials will be required in order to identify populations that may benefit most from valproate for stroke prevention.

BackgroundIntracerebral hemorrhage (ICH) is the most devastating adverse outcome for patients on anticoagulants. Clinical risk scores (CRS) that quantify bleeding risk can guide decision making in situations when indication or duration for anticoagulation is uncertain. We investigated whether integration of a genetic risk score (GRS) into an existing risk factor-based CRS could improve risk stratification for anticoagulation-related ICH.MethodsWe constructed 153 GRS from genome-wide association data of 1,545 ICH cases and 1,481 controls and validated them in 431 ICH cases and 431 matched controls from the population-based UK Biobank. The score that explained the largest variance in ICH risk was selected and tested for prediction of incident ICH in an independent cohort of 5,530 anticoagulant users. A CRS for major anticoagulation-related hemorrhage, based on 8/9 components of the HAS-BLED score, was compared with an enhanced score incorporating an additional point for high genetic risk for ICH (CRS+G).ResultsAmong anticoagulated individuals, 94 ICH occurred over a mean follow-up of 11.9 years. Compared to the lowest GRS tertile, being in the highest tertile was associated with a two-fold increased risk for incident ICH (HR: 2.08 [95% CI 1.22, 3.56]). While the CRS predicted incident ICH with a HR of 1.24 per one point increase (95% CI [1.01, 1.53]), adding a point for high genetic ICH risk led to a stronger association (HR of 1.33 per one point increase, 95% CI [1.11, 1.59]) with improved risk stratification (C-index 0.58 vs. 0.53) and maintained calibration (integrated calibration index 0.001 for both). The new score (CRS+G) showed 20% improvement of high-risk classification among individuals with ICH and a net reclassification improvement of 0.10.ConclusionsAmong anticoagulant users, a prediction score incorporating genomic information is superior to a clinical risk score alone for ICH risk stratification and could serve in clinicaldecision making.

Item does not contain fulltext PURPOSE: Hereditary spastic paraplegia type 4 is extremely variable in age at onset; the same variant can cause onset at birth or in the eighth decade. We recently discovered that missense variants in SPAST, which influences microtubule dynamics, are associated with earlier onset and more severe disease than truncating variants, but even within the early and late-onset groups there remained significant differences in onset. Given the rarity of the condition, we adapted an extreme phenotype approach to identify genetic modifiers of onset. METHODS: We performed a genome-wide association study on 134 patients bearing truncating pathogenic variants in SPAST, divided into early- and late-onset groups (aged ≤15 and ≥45 years, respectively). A replication cohort of 419 included patients carrying either truncating or missense variants. Finally, age at onset was analyzed in the merged cohort (N = 553). RESULTS: We found 1 signal associated with earlier age at onset (rs10775533, P = 8.73E-6) in 2 independent cohorts and in the merged cohort (N = 553, Mantel-Cox test, P < .0001). Western blotting in lymphocytes of 20 patients showed that this locus tends to upregulate SARS2 expression in earlier-onset patients. CONCLUSION: SARS2 overexpression lowers the age of onset in hereditary spastic paraplegia type 4. Lowering SARS2 or improving mitochondrial function could thus present viable approaches to therapy.

Introduction: Epidemiologic studies of intracerebral hemorrhage (ICH) have consistently demonstrated variation in incidence, location, comorbidity burden, age-of-onset, and outcome by race and ethnicity, and genetic studies have identified differences in risk mediated by genetic risk factors such as Apolipoprotein E (APOE). We report the design and methods of the largest multi-ethnic genome-wide association study (GWAS) of ICH risk and outcome conducted to date. Methods: The Ethnic/Racial Variations of ICH Genetics (ERICH-GENE) study is an international, multi-center, genetic case-control study of ICH. Cases are individuals with confirmed primary ICH with biosample availability and consent compatible with shareable genome-wide genotyping or previous genotyping. Central neuroimaging phenotype harmonization of case status, hemorrhage location, and imaging characteristics of cerebral small vessel disease including leukoaraiosis, atrophy, microbleeds, intraventricular hemorrhage severity and volume of ICH measurements will be performed. Controls are ICH-free individuals of compatible age and race/ethnicity from existing studies and biorepositories. Results: As of August 2021, 2,002 ICH cases have been collected and genotyped, in addition to 2,558 already-genotyped ICH cases from the multi-ethnic ERICH study. 5,600 total new ICH cases will be genotyped under ERICH-GENE, with planned meta-analyses across existing ICH GWAS datasets and international biobanks totaling >20,000 cases. We are on schedule to meet our genotyping goal within the study period. Non-European ancestry cases are being prioritized for genotyping and ~66% of the previously genotyped ERICH cases are black or Hispanic. From available cases, a total of 10,621 neuroimaging studies have been uploaded for central adjudication to date with 6,278 having undergone harmonization. Conclusions: ERICH-GENE is a large, multi-ethnic, international, centrally harmonized GWAS of ICH risk and outcome that will identify genetic risk factors across diverse populations for biological discovery and population-specific risk stratification.

Statins lower low-density lipoprotein cholesterol and are widely used for the prevention of atherosclerotic cardiovascular disease. Whether statin-induced low-density lipoprotein reduction increases risk of intracerebral haemorrhage has been debated for almost two decades. Here, we explored whether genetically predicted on-statin low-density lipoprotein response is associated with intracerebral haemorrhage risk using Mendelian randomization. Using genomic data from randomized trials, we derived a polygenic score from 35 single nucleotide polymorphisms of on-statin low-density lipoprotein response and tested it in the population-based UK Biobank. We extracted statin drug and dose information from primary care data on a subset of 225 195 UK Biobank participants covering a period of 29 years. We validated the effects of the genetic score on longitudinal low-density lipoprotein measurements with generalized mixed models and explored associations with incident intracerebral haemorrhage using Cox regression analysis. Statins were prescribed at least once to 75 973 (31%) of the study participants (mean 57 years, 55% females). Among statin users, mean low-density lipoprotein decreased by 3.45 mg/dl per year [95% confidence interval (CI): (−3.47, −3.42)] over follow-up. A higher genetic score of statin response [1 standard deviation (SD) increment] was associated with significant additional reductions in low-density lipoprotein levels [−0.05 mg/dl per year, (−0.07, −0.02)], showed concordant lipidomic effects on other lipid traits as statin use and was associated with a lower risk for incident myocardial infarction [hazard ratio per SD increment 0.98 95% CI (0.96, 0.99)] and peripheral artery disease [hazard ratio per SD increment 0.93 95% CI (0.87, 0.99)]. Over a 11-year follow-up period, a higher genetically predicted statin response among statin users was associated with higher intracerebral haemorrhage risk in a model adjusting for statin dose [hazard ratio per SD increment 1.16, 95% CI (1.05, 1.28)]. On the contrary, there was no association with intracerebral haemorrhage risk among statin non-users (P = 0.89). These results provide further support for the hypothesis that statin-induced low-density lipoprotein reduction may be causally associated with intracerebral haemorrhage risk. While the net benefit of statins for preventing vascular disease is well-established, these results provide insights about the personalized response to statin intake and the role of pharmacological low-density lipoprotein lowering in the pathogenesis of intracerebral haemorrhage.

Background and aims: Combining biologically related traits in genome-wide association studies (GWAS) increases the power for genetic discovery. Given the established relationship between lobar intracerebral hemorrhage (ICH) and cerebral amyloid angiopathy (CAA), and between the latter and levels of cerebrospinal fluid amyloid-β 42 (CSF-Aβ42), we leveraged genetic predisposition for lower CSF-Aβ42 levels as a proxy phenotype for CAA to identify new genes associated with lobar ICH. Methods: We used publicly available GWAS data for CSF-Aβ42 levels (n = 3146) and for lobar ICH (n = 2094). First, we evaluated the association between lobar ICH risk and CSF-Aβ42 in lobar ICH patients using a polygenic risk score (PRS) for CSF-Aβ42. Next, we conducted multi-trait analysis of GWAS (MTAG) for pleiotropy analysis of lobar ICH and CSF-Aβ42. MTAG results were further tested using Expression Quantitative Trait Locus and Differential Gene Expression Analyses. Results: CSF-Aβ42 PRS was associated with lobar ICH risk (p = 0.04). MTAG analysis identified a novel association within CDH9 (rs1007589; minor allele frequency = 0.09; MTAG p = 5.4 × 10−8; lobar ICH odds ratio = 1.4 and p = 2.4 × 10−3; CSF-Aβ42 β = −0.03 and p = 4.5 × 10−6). rs1007589 was significantly associated with the expression levels of CDH9 in temporal and occipital cortices, regions known to preferentially accumulate microhemorrhages in CAA. Conclusion: Our pleiotropy analysis suggested a variant possibly implicated with lobar ICH driven by amyloid-related mechanisms in CDH9 and associated with differential expression in brain regions characteristically affected by CAA. CDH9 is one subtype of the cadherin superfamily, which regulates intercellular adhesion, is involved in blood-brain barrier integrity, and is elevated in Alzheimer’s disease patients. Further analyses are warranted to understand the effects of the variant on the pathogenesis of ICH and its clinical significance.

Introduction: Genome-wide association studies (GWAS) have identified genetic associations for many common diseases and traits. However, incorporating genetic information into disease risk prediction has been challenging because any single collection of variants explains a small proportion of risk. We explored whether combining genetic information from related traits could improve our ability to predict ICH. Methods: We constructed an ICH meta-Genetic Risk Score (metaGRS) using 21 polygenic risk scores (PRSs) from GWASs of traits associated with ICH risk: systolic/diastolic blood pressure, pulse pressure, diabetes, hemoglobin A1c, total cholesterol, high/low-density lipoprotein, triglycerides, body mass index, waist-hip ratio, urine albumin-creatinine ratio, kidney disease, eGFR, white matter hyperintensities, small vessel stroke, insomnia, sleep duration, education attainment, alcohol use and smoking. Each PRS contained common, independent variants at p≤5x10 -4 with each trait. PRSs were calculated in 1,867 ICH cases/1,722 controls, using 1,019 cases/928 controls as a training dataset to derive logORs of the PRSs with ICH status, and a validation dataset of 848 cases/794 controls to construct the metaGRS as a weighted average. Results: Patients in higher metaGRS percentiles had higher odds of ICH (Table) , and a one standard deviation increase in metaGRS was associated with odds of ICH (OR 1.42; 95% CI: 1.28-1.57; p=1.6x10 -11 ). Compared to patients in the middle decile of the metaGRS distribution, patients in the top 10% and 5% had increased odds of ICH (OR 1.87; 95% CI: 1.07-3.30; p=0.03, OR 2.72; 95% CI: 1.54-4.92; p=7.4x10 -4 respectively). Conclusions: A metaGRS identified individuals at high risk for ICH with an odds ratio comparable to traditional risk factors, such as hypertension (OR ~1.6). Further studies are needed to investigate the role of incorporating genetic information into clinical care.

Background: Recent reports have emerged linking SARS-CoV-2 infection to neurological diseases including stroke. It is unclear whether cerebrovascular disease and SARS-CoV-2 share a common risk mechanism, or whether the specific host response to SARS-CoV-2 increases the risk of stroke. We sought to investigate whether genes and pathways associated with SARS-CoV-2 infection and its systemic host response are also related to risk of ischemic stroke (IS) and intracerebral hemorrhage (ICH). Methods: We constructed gene-sets involved with SARS-CoV-2 infection risk and host response. Brain-specific datasets (ROSMAP and Braineac) were used to build co-expression networks for 5 target genes ( ACE2 , TMPRSS2 , BEST3 , ISLR2 and ADAM17 ) involved in SARS-CoV-2 infection phase. Host response gene-sets were constructed from SARS-CoV-2 post-infection gene expression networks measured from lung, kidney, and blood, extracted from literature review. Gene-based association testing was performed using VEGAS2 on GWAS summary data, as well as on data generated through S-PrediXcan analysis of primary tissues relevant to ICH/IS/subtypes. Fisher’s exact test was used to examine gene-set enrichment. Results: The SARS-CoV-2 risk-related ISLR2 co-expression gene network was significantly associated with genetic risk of the large artery stroke (LAS) subtype, across tissues in multiple brain regions (3/10, FDR-p ≤ 0.05), as well as in LAS-relevant primary tissues such as aorta and tibial arteries (p ≤ 0.05). Among SARS-CoV-2 host response factors, SARS-CoV-2 expression changes in lung were found to be enriched for all-cause ischemic stroke risk (p = 0.03), while lobar ICH risk showed an enrichment (p = 0.04) for genes expressed during antiviral response in the blood compartment. Conclusion: Gene networks specific to SARS-CoV-2 infection suggest enrichment in pathways related to infection and host response in both IS and ICH, informed by gene expression levels in multiple brain tissues. Collectively, these findings suggest that increases in stroke risk reported in patients with SARS-CoV-2 infection, particularly large artery stroke, may be intrinsic to this viral infection rather than a more generalized response to severe illness.

Spastic ataxias are rare neurogenetic disorders involving spinocerebellar and pyramidal tracts. Many genes are involved. Among them, CAPN1, when mutated, is responsible for a complex inherited form of spastic paraplegia (SPG76). We report the largest published series of 21 novel patients with nine new CAPN1 disease-causing variants and their clinical characteristics from two European university hospitals (Paris and Stockholm). After a formal clinical examination, causative variants were identified by next-generation sequencing and confirmed by Sanger sequencing. CAPN1 variants are a rare cause (~ 1.4%) of young-adult-onset spastic ataxia; however, together with all published cases, they allowed us to better describe the clinical and genetic spectra of this form. Truncating variants are the most frequent, and missense variants lead to earlier age at onset in favor of an additional deleterious effect. Cerebellar ataxia with cerebellar atrophy, dysarthria and lower limb weakness are often associated with spasticity. We also suggest that cognitive impairment and depression should be assessed specifically in the follow-up of SPG76 cases.

Korrektur zu 10.1038/s41436-020-0899-x

International audience; Hereditary spastic paraplegias are heterogeneous neurodegenerative disorders. Understanding of their pathogenicmechanisms remains sparse, and therapeutic options are lacking. We characterized a mouse model lacking the Cyp2u1 gene, lossof which is known to be involved in a complex form of these diseases in humans. We showed that this model partially recapitulated the clinical and biochemical phenotypes of patients. Using electron microscopy, lipidomic, and proteomicstudies, we identified vitamin B2 as a substrate of the CYP2U1 enzyme, as well as coenzyme Q, neopterin, and IFN-α levels asputative biomarkers in mice and fluids obtained from the largest series of CYP2U1-mutated patients reported so far. We alsoconfirmed brain calcifications as a potential biomarker in patients. Our results suggest that CYP2U1 deficiency disruptsmitochondrial function and impacts proper neurodevelopment, which could be prevented by folate supplementation in ourmouse model, followed by a neurodegenerative process altering multiple neuronal and extraneuronal tissues.

International audience; Purpose: Pathogenic variants in STUB1 were initially described in autosomal recessive spinocerebellar ataxia type 16 and dominant cerebellar ataxia with cerebellar cognitive dysfunction (SCA48).Methods: We analyzed a large series of 440 index cerebellar ataxia cases, mostly with dominant inheritance.Results: STUB1 variants were detected in 50 patients. Age at onset and severity were remarkably variable. Cognitive impairment, predominantly frontal syndrome, was observed in 54% of STUB1 variant carriers, including five families with Huntington or frontotemporal dementia disease-like phenotypes associated with ataxia, while no STUB1 variant was found in 115 patients with frontotemporal dementia. We report neuropathological findings of a STUB1 heterozygous patient, showing massive loss of Purkinje cells in the vermis and major loss in the cerebellar hemispheres without atrophy of the pons, hippocampus, or cerebral cortex. This screening of STUB1 variants revealed new features: (1) the majority of patients were women (70%) and (2) "second hits" in AFG3L2, PRKCG, and TBP were detected in three families suggesting synergic effects.Conclusion: Our results reveal an unexpectedly frequent (7%) implication of STUB1 among dominantly inherited cerebellar ataxias, and suggest that the penetrance of STUB1 variants could be modulated by other factors, including sex and variants in other ataxia-related genes.

Pathogenic variants in STUB1 were initially described in autosomal recessive spinocerebellar ataxia type 16 and dominant cerebellar ataxia with cerebellar cognitive dysfunction (SCA48).We analyzed a large series of 440 index cerebellar ataxia cases, mostly with dominant inheritance.STUB1 variants were detected in 50 patients. Age at onset and severity were remarkably variable. Cognitive impairment, predominantly frontal syndrome, was observed in 54% of STUB1 variant carriers, including five families with Huntington or frontotemporal dementia disease-like phenotypes associated with ataxia, while no STUB1 variant was found in 115 patients with frontotemporal dementia. We report neuropathological findings of a STUB1 heterozygous patient, showing massive loss of Purkinje cells in the vermis and major loss in the cerebellar hemispheres without atrophy of the pons, hippocampus, or cerebral cortex. This screening of STUB1 variants revealed new features: (1) the majority of patients were women (70%) and (2) "second hits" in AFG3L2, PRKCG, and TBP were detected in three families suggesting synergic effects.Our results reveal an unexpectedly frequent (7%) implication of STUB1 among dominantly inherited cerebellar ataxias, and suggest that the penetrance of STUB1 variants could be modulated by other factors, including sex and variants in other ataxia-related genes.

This review aims at updating the clinical and genetic aspects of hereditary spastic paraplegias (HSPs) and hereditary cerebellar ataxias (HCAs), focusing on the concept of spastic-ataxia phenotypic spectrum and on newly identified clinical overlaps with other neurological and nonneurological diseases.Next-generation sequencing (NGS) has allowed the discovery of new genes involved in HSPs and HCAs. They include new HCAs genes such as GRM1 (SCA44), FAT2 (SCA45), PLD3 (SCA46), SCYL1 (SCAR21), UBA5 (SCAR24) and XRCC1 (SCAR26) as well as CAPN1 (SPG76) and CPT1C (SPG73) in HSPs. Furthermore, NGS allowed enriching known genes phenotype, reinforcing the overlap between HSPs and HCAs defining the spastic ataxia spectrum. Clear examples are the expanded phenotypes associated with mutations in SPG7, PNPLA6, GBA2, KIF1C, CYP7B1, FA2H, ATP13A2 and many others. Moreover, other genes not previously linked to HCAs and HSPs have been implicated in spastic or ataxic phenotypes.The increase of HSPs and HCAs-related phenotypes and the continuous discovery of genes complicate clinical diagnostic in practice but, at the same time, it helps highlighting common pathological pathways, therefore opening new ways to the development of common therapeutic approaches.

International audience; Hereditary spastic paraplegias (HSPs) are rare neurological disorders caused by progressive distal degeneration of the corticospinal tracts. Among the 79 loci and 65 spastic paraplegia genes (SPGs) involved in HSPs, mutations in SPAST, which encodes spastin, responsible for SPG4, are the most frequent cause of both familial and sporadic HSP. SPG4 is characterized by a clinically pure phenotype associated with restricted involvement of the corticospinal tracts and posterior columns of the spinal cord. It is rarely associated with additional neurological signs. However, both age of onset and severity of the disorder are extremely variable. Such variability is both intra- and inter-familial and may suggest incomplete penetrance, with some patients carrying mutations remaining asymptomatic for their entire life. We analysed a cohort of 842 patients with SPG4-HSP to assess genotype-phenotype correlations. Most patients were French (89%) and had a family history of SPG4-HSP (75%). Age at onset was characterized by a bimodal distribution, with high inter-familial and intra-familial variability, especially concerning first-degree relatives. Penetrance of the disorder was 0.9, complete after 70 years of age. Penetrance was lower in females (0.88 versus 0.94 in males, P = 0.01), despite a more diffuse phenotype with more frequent upper limb involvement. Seventy-seven per cent of pathogenic mutations (missense, frameshift, splice site, nonsense, and deletions) were located in the AAA cassette of spastin, impairing its microtubule-severing activity. A comparison of the missense and truncating mutations revealed a significantly lower age at onset for patients carrying missense mutations than those carrying truncating mutations, explaining the bimodal distribution of the age at onset. The age at onset for patients carrying missense mutations was often before 10 years, sometimes associated with intellectual deficiency. Neuropathological examination of a single case showed degeneration of the spinocerebellar and spinocortical tracts, as well as the posterior columns. However, there were numerous small-diameter processes among unusually large myelinated fibres in the corticospinal tract, suggesting marked regeneration. In conclusion, this large cohort of 842 individuals allowed us to identify a significantly younger age at onset in missense mutation carriers and lower penetrance in females, despite a more severe disorder. Neuropathology in one case showed numerous small fibres suggesting regeneration.

Hereditary spastic paraplegias (HSPs) are a group of rare inherited neurological diseases characterized by extreme heterogeneity in both their clinical manifestations and genetic backgrounds. Based on symptoms, HSPs can be divided into pure forms, presenting with pyramidal signs leading to lower-limb spasticity, and complex forms, when additional neurological or extraneurological symptoms are detected. The clinical diversity of HSPs partially reflects their underlying genetic backgrounds. To date, 76 loci and 58 corresponding genes [spastic paraplegia genes (SPGs)] have been linked to HSPs. The genetic diagnosis is further complicated by the fact that causative mutations of HSP can be inherited through all possible modes of transmission (autosomal-dominant and -recessive, X-linked, maternal), with some genes showing multiple inheritance patterns. The pathogenic mutations of SPGs primarily lead to progressive degeneration of the upper motor neurons (UMNs) comprising corticospinal tracts. However, it is possible to observe lower-limb muscle atrophy and fasciculations on clinical examination that are clear signs of lower motor neuron (LMN) involvement. The purpose of this review is to classify HSPs based on their degree of motor neuron involvement, distinguishing forms in which only UMNs are affected from those involving both UMN and LMN degeneration, and to describe their differential diagnosis from diseases such as amyotrophic lateral sclerosis.