Publications by authors named "Alexis Brice"

472 Publications

Propensity for somatic expansion increases over the course of life in Huntington disease.

Elife 2021 May 13;10. Epub 2021 May 13.

Sorbonne Université, Paris Brain Institute (ICM Institut du Cerveau), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France.

Recent work on Huntington disease (HD) suggests that somatic instability of CAG repeat tracts, which can expand into the hundreds in neurons, explains clinical outcomes better than the length of the inherited allele. Here, we measured somatic expansion in blood samples collected from the same 50 HD mutation carriers over a twenty-year period, along with post-mortem tissue from 15 adults and 7 fetal mutation carriers, to examine somatic expansions at different stages of life. Post-mortem brains, as previously reported, had the greatest expansions, but fetal cortex had virtually none. Somatic instability in blood increased with age, despite blood cells being short-lived compared to neurons, and was driven mostly by CAG repeat length, then by age at sampling and by interaction between these two variables. Expansion rates were higher in symptomatic subjects. These data lend support to a previously proposed computational model of somatic instability-driven disease.
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http://dx.doi.org/10.7554/eLife.64674DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8118653PMC
May 2021

Primary Progressive Aphasia Associated With Mutations: New Insights Into the Non-amyloid Logopenic Variant.

Neurology 2021 May 12. Epub 2021 May 12.

Sorbonne Université, Paris Brain Institute - Institut du Cerveau (ICM), Inserm U1127, CNRS UMR 7225, AP-HP - Hôpital Pitié-Salpêtrière, Paris, France.

Objective: To determine relative frequencies and linguistic profiles of primary progressive aphasia (PPA) variants associated with progranulin () mutations, and study their neuroanatomical correlates.

Methods: PPA patients carrying mutations (PPA-) were selected amongst a national prospective research cohort of 1,696 frontotemporal dementia (FTD) patients, including 235 patients with PPA. All PPA patients with amyloid-positive CSF biomarkers were excluded. In this cross-sectional study, speech/language and cognitive profiles were characterized with standardized evaluations, and grey matter (GM) atrophy patterns using voxel-based morphometry. Comparisons were performed with controls, and sporadic PPA patients.

Results: Among the overall population of 235 patients, 45 (19%) carried mutations. We studied 32 of these and showed that logopenic PPA (lvPPA) was the most frequent linguistic variant (13, 41%), followed by non-fluent/agrammatic (nfvPPA: 9, 28%) and mixed forms (8, 25%). Semantic variant was rather rare (2, 6%). LvPPA patients, qualified as non-amyloid-lvPPA, presented canonical logopenic deficit. Seven out of 13 had a pure form, six showed subtle additional linguistic deficits not fitting criteria for mixed PPA, hence labelled as "logopenic-spectrum variant". GM atrophy primarily involved left posterior temporal gyrus, mirroring neuroanatomical changes of amyloid-positive-lvPPA. NfvPPA patients presented agrammatism (89%) rather than apraxia of speech (11%).

Conclusions: This study shows that most frequent PPA variant associated with mutations is non-amyloid lvPPA, preceding nfvPPA and mixed forms, and illustrates that language network may be affected at different levels. testing is indicated for PPA patients, whether familial or sporadic. This finding is important for upcoming gene-specific therapies.
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http://dx.doi.org/10.1212/WNL.0000000000012174DOI Listing
May 2021

Genome-wide survival study identifies a novel synaptic locus and polygenic score for cognitive progression in Parkinson's disease.

Nat Genet 2021 Jun 6;53(6):787-793. Epub 2021 May 6.

Translational Genomics Core of Partners HealthCare Personalized Medicine, Cambridge, MA, USA.

A key driver of patients' well-being and clinical trials for Parkinson's disease (PD) is the course that the disease takes over time (progression and prognosis). To assess how genetic variation influences the progression of PD over time to dementia, a major determinant for quality of life, we performed a longitudinal genome-wide survival study of 11.2 million variants in 3,821 patients with PD over 31,053 visits. We discover RIMS2 as a progression locus and confirm this in a replicate population (hazard ratio (HR) = 4.77, P = 2.78 × 10), identify suggestive evidence for TMEM108 (HR = 2.86, P = 2.09 × 10) and WWOX (HR = 2.12, P = 2.37 × 10) as progression loci, and confirm associations for GBA (HR = 1.93, P = 0.0002) and APOE (HR = 1.48, P = 0.001). Polygenic progression scores exhibit a substantial aggregate association with dementia risk, while polygenic susceptibility scores are not predictive. This study identifies a novel synaptic locus and polygenic score for cognitive disease progression in PD and proposes diverging genetic architectures of progression and susceptibility.
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http://dx.doi.org/10.1038/s41588-021-00847-6DOI Listing
June 2021

Genomewide Association Studies of LRRK2 Modifiers of Parkinson's Disease.

Ann Neurol 2021 Jul 17;90(1):76-88. Epub 2021 May 17.

23andMe, Inc., Sunnyvale, CA.

Objective: The aim of this study was to search for genes/variants that modify the effect of LRRK2 mutations in terms of penetrance and age-at-onset of Parkinson's disease.

Methods: We performed the first genomewide association study of penetrance and age-at-onset of Parkinson's disease in LRRK2 mutation carriers (776 cases and 1,103 non-cases at their last evaluation). Cox proportional hazard models and linear mixed models were used to identify modifiers of penetrance and age-at-onset of LRRK2 mutations, respectively. We also investigated whether a polygenic risk score derived from a published genomewide association study of Parkinson's disease was able to explain variability in penetrance and age-at-onset in LRRK2 mutation carriers.

Results: A variant located in the intronic region of CORO1C on chromosome 12 (rs77395454; p value = 2.5E-08, beta = 1.27, SE = 0.23, risk allele: C) met genomewide significance for the penetrance model. Co-immunoprecipitation analyses of LRRK2 and CORO1C supported an interaction between these 2 proteins. A region on chromosome 3, within a previously reported linkage peak for Parkinson's disease susceptibility, showed suggestive associations in both models (penetrance top variant: p value = 1.1E-07; age-at-onset top variant: p value = 9.3E-07). A polygenic risk score derived from publicly available Parkinson's disease summary statistics was a significant predictor of penetrance, but not of age-at-onset.

Interpretation: This study suggests that variants within or near CORO1C may modify the penetrance of LRRK2 mutations. In addition, common Parkinson's disease associated variants collectively increase the penetrance of LRRK2 mutations. ANN NEUROL 2021;90:82-94.
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http://dx.doi.org/10.1002/ana.26094DOI Listing
July 2021

Investigation of Autosomal Genetic Sex Differences in Parkinson's Disease.

Ann Neurol 2021 Jul 24;90(1):35-42. Epub 2021 May 24.

Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, London, UK.

Objective: Parkinson's disease (PD) is a complex neurodegenerative disorder. Men are on average ~ 1.5 times more likely to develop PD compared to women with European ancestry. Over the years, genomewide association studies (GWAS) have identified numerous genetic risk factors for PD, however, it is unclear whether genetics contribute to disease etiology in a sex-specific manner.

Methods: In an effort to study sex-specific genetic factors associated with PD, we explored 2 large genetic datasets from the International Parkinson's Disease Genomics Consortium and the UK Biobank consisting of 13,020 male PD cases, 7,936 paternal proxy cases, 89,660 male controls, 7,947 female PD cases, 5,473 maternal proxy cases, and 90,662 female controls. We performed GWAS meta-analyses to identify distinct patterns of genetic risk contributing to disease in male versus female PD cases.

Results: In total, 19 genomewide significant regions were identified and no sex-specific effects were observed. A high genetic correlation between the male and female PD GWAS were identified (rg = 0.877) and heritability estimates were identical between male and female PD cases (~ 20%).

Interpretation: We did not detect any significant genetic differences between male or female PD cases. Our study does not support the notion that common genetic variation on the autosomes could explain the difference in prevalence of PD between males and females cases at least when considering the current sample size under study. Further studies are warranted to investigate the genetic architecture of PD explained by X and Y chromosomes and further evaluate environmental effects that could potentially contribute to PD etiology in male versus female patients. ANN NEUROL 2021;90:41-48.
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http://dx.doi.org/10.1002/ana.26090DOI Listing
July 2021

Clinical Variability of -Associated Early-Onset Parkinsonism.

Front Neurol 2021 25;12:648457. Epub 2021 Mar 25.

Sorbonne Université, Institut du Cerveau-Paris Brain Institute-ICM, INSERM, CNRS, Assistance Publique Hôpitaux de Paris, Hôpital Pitié-Salpêtrière, CIC Neurosciences, Paris, France.

Autosomal recessive early-onset parkinsonism is clinically and genetically heterogeneous. Mutations of three genes, , and cause pure phenotypes usually characterized by levodopa-responsive Parkinson's disease. By contrast, mutations of other genes, including , and , cause rarer, more severe diseases with a poor response to levodopa, generally with additional atypical features. We performed data mining on a gene panel or whole-exome sequencing in 460 index cases with early-onset (≤ 40 years) Parkinson's disease, including 57 with autosomal recessive disease and 403 isolated cases. We identified two isolated cases carrying biallelic mutations of (double-heterozygous p.D791fs/p.Y232H and homozygous p. Y832C mutations) and two siblings with the recurrent homozygous p.R258Q mutation. All four variants were absent or rare in the Genome Aggregation Database, were predicted to be deleterious on analysis and were found to be highly conserved between species. The patient with both the previously unknown p.D791fs and p.Y232H mutations presented with dystonia-parkinsonism accompanied by a frontal syndrome and oculomotor disturbances at the age of 39. In addition, two siblings from an Algerian consanguineous family carried the homozygous p.R258Q mutation and presented generalized tonic-clonic seizures during childhood, with severe intellectual disability, followed by progressive parkinsonism during their teens. By contrast, the isolated patient with the homozygous p. Y832C mutation, diagnosed at the age of 20, had typical parkinsonism, with no atypical symptoms and slow disease progression. Our findings expand the mutational spectrum and phenotypic profile of -related parkinsonism.
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http://dx.doi.org/10.3389/fneur.2021.648457DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8027075PMC
March 2021

Plasma neurofilament light chain predicts cerebellar atrophy and clinical progression in spinocerebellar ataxia.

Neurobiol Dis 2021 Jun 23;153:105311. Epub 2021 Feb 23.

Sorbonne Université, ICM (Paris Brain Institute), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France; APHP Department of Genetics, Pitié-Salpêtrière University Hospital, Paris, France. Electronic address:

Neurofilament light chain (NfL) is a marker of brain atrophy and predictor of disease progression in rare diseases such as Huntington Disease, but also in more common neurological disorders such as Alzheimer's disease. The aim of this study was to measure NfL longitudinally in autosomal dominant spinocerebellar ataxias (SCAs) and establish correlation with clinical and imaging parameters. We enrolled 62 pathological expansions carriers (17 SCA1, 13 SCA2, 19 SCA3, and 13 SCA7) and 19 age-matched controls in a prospective biomarker study between 2011 and 2015 and followed for 24 months at the Paris Brain Institute. We performed neurological examination, brain 3 T MRI and plasma NfL measurements using an ultrasensitive single-molecule array at baseline and at the two-year follow-up visit. We evaluated NfL correlations with ages, CAG repeat sizes, clinical scores and volumetric brain MRIs. NfL levels were significantly higher in SCAs than controls at both time points (p < 0.001). Age-adjusted NfL levels were significantly correlated at baseline with clinical scores (p < 0.01). We identified optimal NfL cut-off concentrations to differentiate controls from carriers for each genotype (SCA1 16.87 pg/mL, SCA2, 19.1 pg/mL, SCA3 16.04 pg/mL, SCA7 16.67 pg/mL). For all SCAs, NfL concentration was stable over two years (p = 0.95) despite a clinical progression (p < 0.0001). Clinical progression between baseline and follow-up was associated with higher NfL concentrations at baseline (p = 0.04). Of note, all premanifest carriers with NfL levels close to cut off concentrations had signs of the disease at follow-up. For all SCAs, the higher the observed NfL, the lower the pons volume at baseline (p < 0.01) and follow-up (p = 0.02). Higher NfL levels at baseline in all SCAs predicted a decrease in cerebellar volume (p = 0.03). This result remained significant for SCA2 only among all genotypes (p = 0.02). Overall, plasma NfL levels at baseline in SCA expansion carriers predict cerebellar volume change and clinical score progression. NfL levels might help refine inclusion criteria for clinical trials in carriers with very subtle signs.
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http://dx.doi.org/10.1016/j.nbd.2021.105311DOI Listing
June 2021

Response to Park et al.

Genet Med 2021 Jun 24;23(6):1173-1174. Epub 2021 Feb 24.

Sorbonne Université, Institut du Cerveau-Paris Brain Institute (ICM), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France.

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http://dx.doi.org/10.1038/s41436-021-01105-0DOI Listing
June 2021

Genome sequencing analysis identifies new loci associated with Lewy body dementia and provides insights into its genetic architecture.

Nat Genet 2021 03 15;53(3):294-303. Epub 2021 Feb 15.

Reta Lila Weston Institute, UCL Queen Square Institute of Neurology, University College London, London, UK.

The genetic basis of Lewy body dementia (LBD) is not well understood. Here, we performed whole-genome sequencing in large cohorts of LBD cases and neurologically healthy controls to study the genetic architecture of this understudied form of dementia, and to generate a resource for the scientific community. Genome-wide association analysis identified five independent risk loci, whereas genome-wide gene-aggregation tests implicated mutations in the gene GBA. Genetic risk scores demonstrate that LBD shares risk profiles and pathways with Alzheimer's disease and Parkinson's disease, providing a deeper molecular understanding of the complex genetic architecture of this age-related neurodegenerative condition.
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http://dx.doi.org/10.1038/s41588-021-00785-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7946812PMC
March 2021

Increasing involvement of CAPN1 variants in spastic ataxias and phenotype-genotype correlations.

Neurogenetics 2021 03 23;22(1):71-79. Epub 2021 Jan 23.

Sorbonne Université, Institut du Cerveau - Paris Brain Institute - ICM, Inserm, CNRS, APHP, Hôpital de la Pitié Salpêtrière, DMU Neuroscience 6, Paris, France.

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.
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http://dx.doi.org/10.1007/s10048-020-00633-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7997841PMC
March 2021

Novel Homozygous Missense Mutation in the Gene in a Large Sudanese Family.

Front Neurol 2020 29;11:569996. Epub 2020 Oct 29.

Institut du Cerveau, INSERM, CNRS, Sorbonne Université, Paris, France.

Arginases catalyze the last step in the urea cycle. Hyperargininemia, a rare autosomal-recessive disorder of the urea cycle, presents after the first year of age with regression of milestones and evolves gradually into progressive spastic quadriplegia and cognitive dysfunction. Genetic studies reported various mutations in the gene that resulted in hyperargininemia due to a complete or partial loss of arginase activity. Five patients from an extended highly consanguineous Sudanese family presented with regression of the acquired milestones, spastic quadriplegia, and mental retardation. The disease onset ranged from 1 to 3 years of age. Two patients had epileptic seizures and one patient had stereotypic clapping. Genetic testing using whole-exome sequencing, done for the patients and a healthy parent, confirmed the presence of a homozygous novel missense variant in the gene [GRCh37 (NM_001244438.1): exon 4: g.131902487T>A, c.458T>A, p.(Val153Glu)]. The variant was predicted pathogenic by five algorithms and affected a highly conserved amino acid located in the protein domain ureohydrolase, arginase subgroup. Sanger sequencing of 13 sampled family members revealed complete co-segregation between the variant and the disease distribution in the family in line with an autosomal-recessive mode of inheritance. Biochemical analysis confirmed hyperargininemia in five patients. This study reports the first Sudanese family with mutation. The reported variant is a loss-of-function missense mutation. Its pathogenicity is strongly supported by the clinical phenotype, the computational functional impact prediction, the complete co-segregation with the disease, and the biochemical assessment.
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http://dx.doi.org/10.3389/fneur.2020.569996DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7658625PMC
October 2020

Automated Categorization of Parkinsonian Syndromes Using Magnetic Resonance Imaging in a Clinical Setting.

Mov Disord 2021 02 2;36(2):460-470. Epub 2020 Nov 2.

Paris Brain Institute-ICM, INSERM U 1127, CNRS UMR 7225, Sorbonne Université, UMR S 1127, CNRS UMR 7225, Paris, France.

Background: Machine learning algorithms using magnetic resonance imaging (MRI) data can accurately discriminate parkinsonian syndromes. Validation in patients recruited in routine clinical practice is missing.

Objective: The aim of this study was to assess the accuracy of a machine learning algorithm trained on a research cohort and tested on an independent clinical replication cohort for the categorization of parkinsonian syndromes.

Methods: Three hundred twenty-two subjects, including 94 healthy control subjects, 119 patients with Parkinson's disease (PD), 51 patients with progressive supranuclear palsy (PSP) with Richardson's syndrome, 35 with multiple system atrophy (MSA) of the parkinsonian variant (MSA-P), and 23 with MSA of the cerebellar variant (MSA-C), were recruited. They were divided into a training cohort (n = 179) scanned in a research environment and a replication cohort (n = 143) examined in clinical practice on different MRI systems. Volumes and diffusion tensor imaging (DTI) metrics in 13 brain regions were used as input for a supervised machine learning algorithm. To harmonize data across scanners and reduce scanner-dependent effects, we tested two types of normalizations using patient data or healthy control data.

Results: In the replication cohort, high accuracies were achieved using volumetry in the classification of PD-PSP, PD-MSA-C, PSP-MSA-C, and PD-atypical parkinsonism (balanced accuracies: 0.840-0.983, area under the receiver operating characteristic curves: 0.907-0.995). Performances were lower for the classification of PD-MSA-P, MSA-C-MSA-P (balanced accuracies: 0.765-0.784, area under the receiver operating characteristic curve: 0.839-0.871) and PD-PSP-MSA (balanced accuracies: 0.773). Performance using DTI was improved when normalizing by controls, but remained lower than that using volumetry alone or combined with DTI.

Conclusions: A machine learning approach based on volumetry enabled accurate classification of subjects with early-stage parkinsonism, examined on different MRI systems, as part of their clinical assessment. © 2020 International Parkinson and Movement Disorder Society.
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http://dx.doi.org/10.1002/mds.28348DOI Listing
February 2021

Characterization of Recessive Parkinson Disease in a Large Multicenter Study.

Ann Neurol 2020 10 28;88(4):843-850. Epub 2020 Jul 28.

Behavioral Neurology and Movement Disorders Unit, Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey.

Studies of the phenotype and population distribution of rare genetic forms of parkinsonism are required, now that gene-targeting approaches for Parkinson disease have reached the clinical trial stage. We evaluated the frequencies of PRKN, PINK1, and DJ-1 mutations in a cohort of 1,587 cases. Mutations were found in 14.1% of patients; 27.6% were familial and 8% were isolated. PRKN was the gene most frequently mutated in Caucasians, whereas PINK1 mutations predominated in Arab-Berber individuals. Patients with PRKN mutations had an earlier age at onset, and less asymmetry, levodopa-induced motor complications, dysautonomia, and dementia than those without mutations. ANN NEUROL 2020;88:843-850.
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http://dx.doi.org/10.1002/ana.25787DOI Listing
October 2020

Differences in the Presentation and Progression of Parkinson's Disease by Sex.

Mov Disord 2021 01 1;36(1):106-117. Epub 2020 Oct 1.

Department of Neurology, Nottingham University NHS Trust, Nottingham, UK.

Background: Previous studies reported various symptoms of Parkinson's disease (PD) associated with sex. Some were conflicting or confirmed in only one study.

Objectives: We examined sex associations to PD phenotypes cross-sectionally and longitudinally in large-scale data.

Methods: We tested 40 clinical phenotypes, using longitudinal, clinic-based patient cohorts, consisting of 5946 patients, with a median follow-up of 3.1 years. For continuous outcomes, we used linear regressions at baseline to test sex-associated differences in presentation, and linear mixed-effects models to test sex-associated differences in progression. For binomial outcomes, we used logistic regression models at baseline and Cox regression models for survival analyses. We adjusted for age, disease duration, and medication use. In the secondary analyses, data from 17 719 PD patients and 7588 non-PD participants from an online-only, self-assessment PD cohort were cross-sectionally evaluated to determine whether the sex-associated differences identified in the primary analyses were consistent and unique to PD.

Results: Female PD patients had a higher risk of developing dyskinesia early during the follow-up period, with a slower progression in activities of daily living difficulties, and a lower risk of developing cognitive impairments compared with male patients. The findings in the longitudinal, clinic-based cohorts were mostly consistent with the results of the online-only cohort.

Conclusions: We observed sex-associated contributions to PD heterogeneity. These results highlight the necessity of future research to determine the underlying mechanisms and importance of personalized clinical management. © 2020 International Parkinson and Movement Disorder Society.
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http://dx.doi.org/10.1002/mds.28312DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7883324PMC
January 2021

Isolated parkinsonism is an atypical presentation of GRN and C9orf72 gene mutations.

Parkinsonism Relat Disord 2020 11 15;80:73-81. Epub 2020 Sep 15.

Sorbonne Université, Paris Brain Institute - Institut du Cerveau - ICM, Inserm U1127, CNRS UMR 7225, AP-HP - Hôpital Pitié-Salpêtrière, Paris, France; Centre de Référence des Démences Rares ou Précoces, IM2A, Département de Neurologie, AP-HP - Hôpital Pitié-Salpêtrière, Paris, France; Département de Neurologie, AP-HP - Hôpital Pitié-Salpêtrière, Paris, France; Paris Brain Institute - Institut du Cerveau - ICM, FrontLab, Paris, France. Electronic address:

Introduction: A phenotype of isolated parkinsonism mimicking Idiopathic Parkinson's Disease (IPD) is a rare clinical presentation of GRN and C9orf72 mutations, the major genetic causes of frontotemporal dementia (FTD). It still remains controversial if this association is fortuitous or not, and which clinical clues could reliably suggest a genetic FTD etiology in IPD patients. This study aims to describe the clinical characteristics of FTD mutation carriers presenting with IPD phenotype, provide neuropathological evidence of the mutation's causality, and specifically address their "red flags" according to current IPD criteria.

Methods: Seven GRN and C9orf72 carriers with isolated parkinsonism at onset, and three patients from the literature were included in this study. To allow better delineation of their phenotype, the presence of supportive, exclusion and "red flag" features from MDS criteria were analyzed for each case.

Results: Amongst the ten patients (5 GRN, 5 C9orf72), seven fulfilled probable IPD criteria during all the disease course, while behavioral/language or motoneuron dysfunctions occurred later in three. Disease duration was longer and dopa-responsiveness was more sustained in C9orf72 than in GRN carriers. Subtle motor features, cognitive/behavioral changes, family history of dementia/ALS were suggestive clues for a genetic diagnosis. Importantly, neuropathological examination in one patient revealed typical TDP-43-inclusions without alpha-synucleinopathy, thus demonstrating the causal link between FTD mutations, TDP-43-pathology and PD phenotype.

Conclusion: We showed that, altogether, family history of early-onset dementia/ALS, the presence of cognitive/behavioral dysfunction and subtle motor characteristics are atypical features frequently present in the parkinsonian presentations of GRN and C9orf72 mutations.
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http://dx.doi.org/10.1016/j.parkreldis.2020.09.019DOI Listing
November 2020

Segregation of ATP10B variants in families with autosomal recessive parkinsonism.

Acta Neuropathol 2020 11 5;140(5):783-785. Epub 2020 Sep 5.

Sorbonne Université, Institut du Cerveau-Paris Brain Institute-ICM, Hôpital de la Salpêtrière, Inserm U 1127, CNRS UMR 7225, 75013, Paris, France.

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http://dx.doi.org/10.1007/s00401-020-02219-6DOI Listing
November 2020

Analysis of DNM3 and VAMP4 as genetic modifiers of LRRK2 Parkinson's disease.

Neurobiol Aging 2021 01 13;97:148.e17-148.e24. Epub 2020 Jul 13.

Research Unit U1127 at INSERM, Research Unit UMR 7225 at the French National Centre for Scientific Research (CNRS) Research Unit UMR_1127 at Sorbonne Université, Institutet du Cerveau et de la Moëlle épinière (ICM), Paris, France.

The LRRK2 gene has rare (p.G2019S) and common risk variants for Parkinson's disease (PD). DNM3 has previously been reported as a genetic modifier of the age at onset in PD patients carrying the LRRK2 p.G2019S mutation. We analyzed this effect in a new cohort of LRRK2 p.G2019S heterozygotes (n = 724) and meta-analyzed our data with previously published data (n = 754). VAMP4 is in close proximity to DNM3, and was associated with PD in a recent study, so it is possible that variants in this gene may be important. We also analyzed the effect of VAMP4 rs11578699 on LRRK2 penetrance. Our analysis of DNM3 in previously unpublished data does not show an effect on age at onset in LRRK2 p.G2019S carriers; however, the inter-study heterogeneity may indicate ethnic or population-specific effects of DNM3. There was no evidence for linkage disequilibrium between DNM3 and VAMP4. Analysis of sporadic patients stratified by the risk variant LRRK2 rs10878226 indicates a possible interaction between common variation in LRRK2 and VAMP4 in disease risk.
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http://dx.doi.org/10.1016/j.neurobiolaging.2020.07.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7762821PMC
January 2021

Early cognitive decline after bilateral subthalamic deep brain stimulation in Parkinson's disease patients with GBA mutations.

Parkinsonism Relat Disord 2020 07 9;76:56-62. Epub 2020 Jun 9.

Sorbonne Université, Inserm U1127, CNRS UMR 7225, Institut du Cerveau et de la Moelle épinière, Paris, France; Assistance Publique Hôpitaux de Paris, Hôpital Pitié-Salpêtrière, Département de Neurologie, Clinical Research Center Neurosciences, Paris, France. Electronic address:

Background: Subthalamic nucleus deep brain stimulation (STN-DBS) has demonstrated its efficacy on motor complications in advanced Parkinson's disease (PD) but does not modify disease progression. Genetic forms of PD have been associated with different cognitive progression profiles.

Objective: To assess the effect of PD-related genetic mutations on cognitive outcome after STN-DBS.

Methods: Patients with STN-DBS were screened for LRRK2, GBA, and PRKN mutations at the Pitié-Salpêtrière Hospital between 1997 and 2009. Patients with known monogenetic forms of PD from six other centers were also included. The Mattis Dementia Rating Scale (MDRS) was used to evaluate cognition at baseline and one-year post-surgery. The standardized Unified PD Rating Scale (UPDRS) evaluation On and Off medication/DBS was also administered. A generalized linear model adjusted for sex, ethnicity, age at onset, and disease duration was used to evaluate the effect of genetic factors on MDRS changes.

Results: We analyzed 208 patients (131 males, 77 females, 54.3 ± 8.8 years) including 25 GBA, 18 LRRK2, 22 PRKN, and 143 PD patients without mutations. PRKN patients were younger and had a longer disease duration at baseline. A GBA mutation was the only significant genetic factor associated with MDRS change (β = -2.51, p = 0.009). GBA mutation carriers had a more pronounced post-operative MDRS decline (3.2 ± 5.1) than patients with LRRK2 (0.9 ± 4.8), PRKN (0.5 ± 2.7) or controls (1.4 ± 4.4). The motor response to DBS was similar between groups.

Conclusion: GBA mutations are associated with early cognitive decline following STN-DBS. Neuropsychological assessment and discussions on the benefit/risk ratio of DBS are particularly important for this population.
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http://dx.doi.org/10.1016/j.parkreldis.2020.04.002DOI Listing
July 2020

Genetic and Phenotypic Basis of Autosomal Dominant Parkinson's Disease in a Large Multi-Center Cohort.

Front Neurol 2020 28;11:682. Epub 2020 Jul 28.

Sorbonne Université, Unité Mixte de Recherche (UMR) 1127, Paris, France.

, and are unequivocally associated with autosomal dominant Parkinson's disease (PD). We evaluated the prevalence of , and mutations and associated clinical features in a large French multi-center cohort of PD patients. Demographic and clinical data were collected for 1,805 index cases (592 with autosomal dominant inheritance and 1,213 isolated cases) since 1990. All probands were screened with TaqMan assays for Gly2019Ser. In the absence of this mutation, the coding sequences of the three genes were analyzed by Sanger sequencing and/or next-generation sequencing. The data for the three genes were analyzed according to age at onset, family history, ethnic origin and clinical features. We identified 160 index cases (8.9%) with known pathogenic variants: 138 with pathogenic variants (7.6%), including 136 with the Gly2019Ser mutation, 19 with point mutations or genomic rearrangements (1.1%), and three with the Asp620Asn mutation (0.16%). Mutation frequencies were higher in familial than isolated cases, consistent with autosomal dominant inheritance (12.0 vs. 7.3%; OR 1.7, 95% CI [1.2-2.4], = 0.001). PD patients with variants were more likely to have higher rates of late-onset PD (>50 years; OR 1.5, 95% CI [1.0-2.1], = 0.03), whereas those with mutations tended to have earlier age at onset disease (≤ 50 years, = 0.06). The clinical features of carriers and those without any pathogenic variants in known PD-associated genes were similar. The likelihood of detecting disease-causing mutations was higher in cases compatible with autosomal dominant inheritance.
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http://dx.doi.org/10.3389/fneur.2020.00682DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7399219PMC
July 2020

Exome Sequencing Reveals Signal Transduction Genes Involved in Impulse Control Disorders in Parkinson's Disease.

Front Neurol 2020 21;11:641. Epub 2020 Jul 21.

Sorbonne Université, INSERM UMRS 1127, CNRS UMR 7225, Institut du Cerveau et de la Moelle, ICM, Paris, France.

Impulse control disorders (ICDs) frequently complicate dopamine agonist (DA) therapy in Parkinson's disease (PD). There is growing evidence of a high heritability for ICDs in the general population and in PD. Variants on genes belonging to the reward pathway have been shown to account for part of this heritability. We aimed to identify new pathways associated with ICDs in PD. Thirty-six Parkinsonian patients on DA therapy with ( = 18) and without ICDs ( = 18) matched on age at PD's onset, and gender was selected to represent the most extreme phenotypes of their category. Exome sequencing was performed, and variants with a strong functional impact in brain-expressed genes were selected. Allele frequencies and their distribution in genes and pathways were analyzed with single variant and SKAT-O tests. The 10 most associated variants, genes, and pathways were retained for replication in the Parkinson's progression markers initiative (PPMI) cohort. None of markers tested passed the significance threshold adjusted for multiple comparisons. However, the "Adenylate cyclase activating" pathway, one of the top associated pathways in the discovery data set ( = 1.6 × 10) was replicated in the PPMI cohort and was significantly associated with ICDs in a pooled analysis (combined value 3.3 × 10). Two of the 10 most associated variants belonged to genes implicated in cAMP and ERK signaling (rs34193571 in = 5 × 10; rs1877652 in = 8 × 10) although non-significant after Bonferroni correction. Our results suggest that genes implicated in the signaling pathways linked to G protein-coupled receptors participate to genetic susceptibility to ICDs in PD.
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http://dx.doi.org/10.3389/fneur.2020.00641DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7385236PMC
July 2020

Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment.

Genet Med 2020 11 27;22(11):1851-1862. Epub 2020 Jul 27.

Sorbonne Université, Institut du Cerveau-Paris Brain Institute (ICM), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France.

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.
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http://dx.doi.org/10.1038/s41436-020-0899-xDOI Listing
November 2020

Nonsteroidal Anti-inflammatory Use and LRRK2 Parkinson's Disease Penetrance.

Mov Disord 2020 10 14;35(10):1755-1764. Epub 2020 Jul 14.

Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, New York, USA.

Background: The penetrance of leucine rich repeat kinase 2 (LRRK2) mutations is incomplete and may be influenced by environmental and/or other genetic factors. Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to reduce inflammation and may lower Parkinson's disease (PD) risk, but their role in LRRK2-associated PD is unknown.

Objectives: The objective of this study is to evaluate the association of regular NSAID use and LRRK2-associated PD.

Methods: Symptomatic ("LRRK2-PD") and asymptomatic ("LRRK2-non-PD") participants with LRRK2 G2019S, R1441X, or I2020T variants (definitely pathogenic variant carriers) or G2385R or R1628P variants (risk variant carriers) from 2 international cohorts provided information on regular ibuprofen and/or aspirin use (≥2 pills/week for ≥6 months) prior to the index date (diagnosis date for PD, interview date for non-PD). Multivariate logistic regression was used to evaluate the relationship between regular NSAID use and PD for any NSAID, separately for ibuprofen and aspirin in all carriers and separately in pathogenic and risk variant groups.

Results: A total of 259 LRRK2-PD and 318 LRRK2-non-PD participants were enrolled. Regular NSAID use was associated with reduced odds of PD in the overall cohort (odds ratio [OR], 0.34; 95% confidence interval [CI], 0.21-0.57) and in both pathogenic and risk variant carriers (OR , 0.38; 95% CI, 0.21-0.67 and OR , 0.19; 95% CI, 0.04-0.99). Similar associations were observed for ibuprofen and aspirin separately (OR , 0.19; 95% CI, 0.07-0.50 and OR , 0.51; 95% CI, 0.28-0.91).

Conclusions: Regular NSAID use may be associated with reduced penetrance in LRRK2-associated PD. The LRRK2 protein is involved in inflammatory pathways and appears to be modulated by regular anti-inflammatory use. Longitudinal observational and interventional studies of NSAID exposure and LRRK2-PD are needed to confirm this association. © 2020 International Parkinson and Movement Disorder Society.
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http://dx.doi.org/10.1002/mds.28189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7572560PMC
October 2020

Gene Panel Sequencing Identifies Novel Pathogenic Mutations in Moroccan Patients with Familial Parkinson Disease.

J Mol Neurosci 2021 Jan 16;71(1):142-152. Epub 2020 Jun 16.

Neurology and Neurogenetics, Faculty of Medicine and Pharmacy, Genomics Center of Human Pathologies, University Mohammed V, Rabat, Morocco.

In the past two decades, genetic studies of familial forms of Parkinson's disease (PD) have shown evidence that PD has a significant genetic component. Indeed, 12 genes are strongly involved in PD causality, three of them having dominant inheritance and 9 causing early-onset autosomal recessive forms, including 3 with a typical PD and 6 with an atypical parkinsonism. The aim of this study was to determine the genetic basis of familial PD in Moroccan patients. We selected 18 Moroccan index case with familial forms of PD. Patients were first screened for exon-rearrangements by MLPA kit. They were then analyzed by gene panel next-generation sequencing (NGS). Functional variants with minor allele frequencies < 0.5% in public databases were considered potential candidate variants to PD. In the 18 PD patients with a positive family history that were analyzed, MLPA assays identified PRKN deletions in two patients: a homozygous exon 3-5 deletion and a heterozygous exon 4 deletion. Sixteen rare SNV were identified by NGS, four of them were novel. Seven mutations were categorized as pathogenic, five as likely pathogenic, two to be of uncertain significance, and 3 were predicted to be likely benign but may give a weaker pathogenic effect and could contribute to PD since they were found in late-onset PD patients. Rare or novel mutations that could be related to the disease were identified in 72% of these patients (13/18), including nine with bi-allelic pathogenic/likely pathogenic variants in genes causing recessive PD, particularly PRKN and PINK1. Mutations in genes with dominant inheritance were found in 4/18 patients (22%).
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http://dx.doi.org/10.1007/s12031-020-01635-3DOI Listing
January 2021

Characterization of recessive Parkinson's disease in a large multicenter study.

Ann Neurol 2020 May 30. Epub 2020 May 30.

Behavioural Neurology and Movement Disorders Unit, Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey.

Studies of the phenotype and population distribution of rare genetic forms of parkinsonism are required, now that gene-targeting approaches for Parkinson's disease have reached the clinical trial stage. We evaluated the frequencies of PRKN, PINK1, and DJ-1 mutations in a cohort of 1587 cases. Mutations were found in 14.1% of patients: 27.6% were familial and 8% were isolated. PRKN was the gene most frequently mutated in Caucasians whereas PINK1 mutations predominated in Arab-Berber individuals. Patients with PRKN mutations had an earlier age at onset, and less asymmetry, levodopa-induced motor complications, dysautonomia, and dementia than those without mutations. This article is protected by copyright. All rights reserved.
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http://dx.doi.org/10.1002/ana.25787DOI Listing
May 2020

Plasma progranulin levels for frontotemporal dementia in clinical practice: a 10-year French experience.

Neurobiol Aging 2020 07 21;91:167.e1-167.e9. Epub 2020 Feb 21.

Université Paris-Saclay, CEA, CNRS, Inserm, BioMaps, Orsay, France.

GRN mutations are frequent causes of familial frontotemporal degeneration. Although there is no clear consensual threshold, plasma progranulin levels represent an efficient biomarker for predicting GRN mutations when decreased. We evaluated plasma levels to determine whether it could also predict age at onset, clinical phenotype, or disease progression in 160 GRN carriers. Importantly, progranulin levels were influenced by gender, with lower levels in male than in female patients in our study. Although we found no correlation with age at onset or with clinical phenotype, we confirmed that decreased level predicts GRN mutations, even in presymptomatic carriers more than four decades before disease onset. We also provided first evidence for the stability of levels throughout longitudinal trajectory in carriers, over a 4-year time span. Finally, we confirmed that progranulin levels constitute a reliable, cost-effective marker, suitable as a screening tool in patients with familial frontotemporal degeneration, and more broadly in patients without family history or with atypical presentations who are less likely to be referred for molecular diagnosis.
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http://dx.doi.org/10.1016/j.neurobiolaging.2020.02.014DOI Listing
July 2020

Homozygous GRN mutations: new phenotypes and new insights into pathological and molecular mechanisms.

Brain 2020 01;143(1):303-319

Sorbonne Université, Institut du Cerveau et de la Moelle épinière (ICM), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France.

Homozygous mutations in the progranulin gene (GRN) are associated with neuronal ceroid lipofuscinosis 11 (CLN11), a rare lysosomal-storage disorder characterized by cerebellar ataxia, seizures, retinitis pigmentosa, and cognitive disorders, usually beginning between 13 and 25 years of age. This is a rare condition, previously reported in only four families. In contrast, heterozygous GRN mutations are a major cause of frontotemporal dementia associated with neuronal cytoplasmic TDP-43 inclusions. We identified homozygous GRN mutations in six new patients. The phenotypic spectrum is much broader than previously reported, with two remarkably distinct presentations, depending on the age of onset. A childhood/juvenile form is characterized by classical CLN11 symptoms at an early age at onset. Unexpectedly, other homozygous patients presented a distinct delayed phenotype of frontotemporal dementia and parkinsonism after 50 years; none had epilepsy or cerebellar ataxia. Another major finding of this study is that all GRN mutations may not have the same impact on progranulin protein synthesis. A hypomorphic effect of some mutations is supported by the presence of residual levels of plasma progranulin and low levels of normal transcript detected in one case with a homozygous splice-site mutation and late onset frontotemporal dementia. This is a new critical finding that must be considered in therapeutic trials based on replacement strategies. The first neuropathological study in a homozygous carrier provides new insights into the pathological mechanisms of the disease. Hallmarks of neuronal ceroid lipofuscinosis were present. The absence of TDP-43 cytoplasmic inclusions markedly differs from observations of heterozygous mutations, suggesting a pathological shift between lysosomal and TDP-43 pathologies depending on the mono or bi-allelic status. An intriguing observation was the loss of normal TDP-43 staining in the nucleus of some neurons, which could be the first stage of the TDP-43 pathological process preceding the formation of typical cytoplasmic inclusions. Finally, this study has important implications for genetic counselling and molecular diagnosis. Semi-dominant inheritance of GRN mutations implies that specific genetic counselling should be delivered to children and parents of CLN11 patients, as they are heterozygous carriers with a high risk of developing dementia. More broadly, this study illustrates the fact that genetic variants can lead to different phenotypes according to their mono- or bi-allelic state, which is a challenge for genetic diagnosis.
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http://dx.doi.org/10.1093/brain/awz377DOI Listing
January 2020

Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome.

Tremor Other Hyperkinet Mov (N Y) 2019 22;9. Epub 2019 Nov 22.

INSERM, U 1127, CNRS UMR 7225, Faculté de Médecine de Sorbonne Université, UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Hôpital Pitié-Salpêtrière, 47-83 Boulevard de l'Hôpital, 75013 Paris, FR.

Background: Genes involved in Tourette syndrome (TS) remain largely unknown. We aimed to identify genetic factors contributing to TS in a French cohort of 120 individuals using a combination of hypothesis-driven and exome-sequencing approaches.

Methods: We first sequenced exons of and in the TS cohort and subsequently sequenced the exome of 12 individuals harboring rare variants in these genes to find additional rare variants contributing to the disorder under the hypothesis of oligogenic inheritance. We further screened three candidate genes (, , and ) preferentially expressed in the basal ganglia, and three additional genes involved in neurotensin and opioid signaling (, , and ), and compared variant frequencies in TS patients and 788 matched control individuals. We also investigated the impact of altering the expression of in zebrafish.

Results: Thirteen ultrarare missense variants of and were identified in 12 patients. Exome sequencing in these patients revealed rare possibly deleterious variants in 3,041 genes, 54 of which were preferentially expressed in the basal ganglia. Comparison of variant frequencies altering selected candidate genes in TS and control individuals revealed an excess of potentially disrupting variants in , encoding the opioid kappa receptor, in TS patients. Accordingly, we show that downregulation of the orthologue in zebrafish induces a hyperkinetic phenotype in early development.

Discussion: These results support a heterogeneous and complex genetic etiology of TS, possibly involving rare variants altering the opioid pathway in some individuals, which could represent a novel therapeutic target in this disorder.
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http://dx.doi.org/10.7916/tohm.v0.693DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6878848PMC
September 2020

Age at symptom onset and death and disease duration in genetic frontotemporal dementia: an international retrospective cohort study.

Lancet Neurol 2020 02 3;19(2):145-156. Epub 2019 Dec 3.

Institut du Cerveau et de la Moelle épinière & Centre de Référence des Démences Rares ou précoces, Institut de la Mémoire et de la Maladie d'Alzheimer, Assistance Publique-Hôpitaux de Paris, Hôpital de la Pitié-Salpêtrière, Paris, France.

Background: Frontotemporal dementia is a heterogenous neurodegenerative disorder, with about a third of cases being genetic. Most of this genetic component is accounted for by mutations in GRN, MAPT, and C9orf72. In this study, we aimed to complement previous phenotypic studies by doing an international study of age at symptom onset, age at death, and disease duration in individuals with mutations in GRN, MAPT, and C9orf72.

Methods: In this international, retrospective cohort study, we collected data on age at symptom onset, age at death, and disease duration for patients with pathogenic mutations in the GRN and MAPT genes and pathological expansions in the C9orf72 gene through the Frontotemporal Dementia Prevention Initiative and from published papers. We used mixed effects models to explore differences in age at onset, age at death, and disease duration between genetic groups and individual mutations. We also assessed correlations between the age at onset and at death of each individual and the age at onset and at death of their parents and the mean age at onset and at death of their family members. Lastly, we used mixed effects models to investigate the extent to which variability in age at onset and at death could be accounted for by family membership and the specific mutation carried.

Findings: Data were available from 3403 individuals from 1492 families: 1433 with C9orf72 expansions (755 families), 1179 with GRN mutations (483 families, 130 different mutations), and 791 with MAPT mutations (254 families, 67 different mutations). Mean age at symptom onset and at death was 49·5 years (SD 10·0; onset) and 58·5 years (11·3; death) in the MAPT group, 58·2 years (9·8; onset) and 65·3 years (10·9; death) in the C9orf72 group, and 61·3 years (8·8; onset) and 68·8 years (9·7; death) in the GRN group. Mean disease duration was 6·4 years (SD 4·9) in the C9orf72 group, 7·1 years (3·9) in the GRN group, and 9·3 years (6·4) in the MAPT group. Individual age at onset and at death was significantly correlated with both parental age at onset and at death and with mean family age at onset and at death in all three groups, with a stronger correlation observed in the MAPT group (r=0·45 between individual and parental age at onset, r=0·63 between individual and mean family age at onset, r=0·58 between individual and parental age at death, and r=0·69 between individual and mean family age at death) than in either the C9orf72 group (r=0·32 individual and parental age at onset, r=0·36 individual and mean family age at onset, r=0·38 individual and parental age at death, and r=0·40 individual and mean family age at death) or the GRN group (r=0·22 individual and parental age at onset, r=0·18 individual and mean family age at onset, r=0·22 individual and parental age at death, and r=0·32 individual and mean family age at death). Modelling showed that the variability in age at onset and at death in the MAPT group was explained partly by the specific mutation (48%, 95% CI 35-62, for age at onset; 61%, 47-73, for age at death), and even more by family membership (66%, 56-75, for age at onset; 74%, 65-82, for age at death). In the GRN group, only 2% (0-10) of the variability of age at onset and 9% (3-21) of that of age of death was explained by the specific mutation, whereas 14% (9-22) of the variability of age at onset and 20% (12-30) of that of age at death was explained by family membership. In the C9orf72 group, family membership explained 17% (11-26) of the variability of age at onset and 19% (12-29) of that of age at death.

Interpretation: Our study showed that age at symptom onset and at death of people with genetic frontotemporal dementia is influenced by genetic group and, particularly for MAPT mutations, by the specific mutation carried and by family membership. Although estimation of age at onset will be an important factor in future pre-symptomatic therapeutic trials for all three genetic groups, our study suggests that data from other members of the family will be particularly helpful only for individuals with MAPT mutations. Further work in identifying both genetic and environmental factors that modify phenotype in all groups will be important to improve such estimates.

Funding: UK Medical Research Council, National Institute for Health Research, and Alzheimer's Society.
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http://dx.doi.org/10.1016/S1474-4422(19)30394-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7007771PMC
February 2020

Genetic modifiers of risk and age at onset in GBA associated Parkinson's disease and Lewy body dementia.

Brain 2020 01;143(1):234-248

Institute of Clinical Medicine, Department of Neurology, University of Oulu, Oulu, Finland.

Parkinson's disease is a genetically complex disorder. Multiple genes have been shown to contribute to the risk of Parkinson's disease, and currently 90 independent risk variants have been identified by genome-wide association studies. Thus far, a number of genes (including SNCA, LRRK2, and GBA) have been shown to contain variability across a spectrum of frequency and effect, from rare, highly penetrant variants to common risk alleles with small effect sizes. Variants in GBA, encoding the enzyme glucocerebrosidase, are associated with Lewy body diseases such as Parkinson's disease and Lewy body dementia. These variants, which reduce or abolish enzymatic activity, confer a spectrum of disease risk, from 1.4- to >10-fold. An outstanding question in the field is what other genetic factors that influence GBA-associated risk for disease, and whether these overlap with known Parkinson's disease risk variants. Using multiple, large case-control datasets, totalling 217 165 individuals (22 757 Parkinson's disease cases, 13 431 Parkinson's disease proxy cases, 622 Lewy body dementia cases and 180 355 controls), we identified 1691 Parkinson's disease cases, 81 Lewy body dementia cases, 711 proxy cases and 7624 controls with a GBA variant (p.E326K, p.T369M or p.N370S). We performed a genome-wide association study and analysed the most recent Parkinson's disease-associated genetic risk score to detect genetic influences on GBA risk and age at onset. We attempted to replicate our findings in two independent datasets, including the personal genetics company 23andMe, Inc. and whole-genome sequencing data. Our analysis showed that the overall Parkinson's disease genetic risk score modifies risk for disease and decreases age at onset in carriers of GBA variants. Notably, this effect was consistent across all tested GBA risk variants. Dissecting this signal demonstrated that variants in close proximity to SNCA and CTSB (encoding cathepsin B) are the most significant contributors. Risk variants in the CTSB locus were identified to decrease mRNA expression of CTSB. Additional analyses suggest a possible genetic interaction between GBA and CTSB and GBA p.N370S induced pluripotent cell-derived neurons were shown to have decreased cathepsin B expression compared to controls. These data provide a genetic basis for modification of GBA-associated Parkinson's disease risk and age at onset, although the total contribution of common genetics variants is not large. We further demonstrate that common variability at genes implicated in lysosomal function exerts the largest effect on GBA associated risk for disease. Further, these results have implications for selection of GBA carriers for therapeutic interventions.
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http://dx.doi.org/10.1093/brain/awz350DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6935749PMC
January 2020