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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.

Background: Genetic mutations causing autosomal recessive Parkinson's disease account for a significant proportion of patients with early-onset disease. However, no large multicentre studies of known recessive Parkinson's disease-linked genes have been performed, to guide genetic testing according to age at onset, family history, ethnic origin, or phenotype. We aimed to evaluate the relative frequencies of mutations in genes causing recessive Parkinson's disease and their associated phenotypes in a large series of European and North African cases. Methods: Clinical data for 1664 patients were collected between 1990 and 2018 from 511 families with recessive Parkinson's disease and/or with consanguinity, and 1098 isolated cases. All the recessively inherited genes were screened by Sanger and/or targeted next-generation sequencing and gene dosage methods. Clinical features were compared between patients with PRKN and those without mutations, by regression analyses adjusted for sex, age at onset, disease duration and levodopa medication. Findings: Biallelic mutations of genes known to cause recessive Parkinson's disease were found in 246 of the 1609 index cases (15·3%): 150 familial (29·4%) and 96 (8·7%) isolated cases. The most frequently mutated genes were PRKN, in 199 cases (12·4%), PINK1, in 23 (1·8%), and DJ-1, in two (0·16%). We screened 675 index cases by targeted sequencing, and 22 were found to have mutations in genes known to cause atypical parkinsonism (3·3%). PRKN and PINK1 mutation frequencies were higher in early-onset (≤40 years) than late-onset Parkinson's disease. The frequency of PRKN mutations in the 1609 index cases decreased with increasing age at onset, from 38% in cases ≤20 years to 4·4% in those with onset at 41 to 60 years. No mutation of PRKN or another recessive Parkinson's disease gene was found in patients with onset above 60. PRKN mutations were more frequent in Caucasians (13·4%) than in North Africans (7·4%). Conversely, PINK1 mutations were more frequent in North Africans (6·3%) than in Caucasians (0·9%). PRKN patients had an earlier age at onset, lower levels of asymmetry, akinesia, levodopa-induced motor complications, dysautonomia, and dementia than those without mutations. Interpretation: This is a large study providing information about the frequency of recessive Parkinson's disease genes according to age at onset, family history, ethnic origin, and associated phenotype. Its findings will be useful for genetic testing and counselling. Funding Statement: Fondation de France, France-Parkinson Association, la Federation pour la Recherche sur le Cerveau, the French program "Investissements d'avenir", National Institute for Health Research. Declaration of Interests: SL reports grants from Fondation de France, the French program “Investissements d’avenir” (ANR-10-IAIHU-06), both outside the scope of the submitted work. MA reports grants and personal fees from Abbvie, Teva, Aguettant, Actelion Pharmaceuticals, personal fees from Johnson and Johnson, Merz, Orkyn, all outside the scope of the submitted work. ER reports grants, personal fees and non-financial support from Orkyn, Aguettant, Merz pharma, Everpharma, personal fees and non-financial support from Movement Disorders Society, grants and non-financial support from Elivie, non-financial support from Merck, Dystonia Coalition, Dystonia Medical Research Foundation, grants from Ipsen, Fondation Desmarest, Fonds de dotation Brou de Lauriere, Agence Nationale de la Recherche, AMADYS, personal fees from Medday pharma, Retrophin, European Academy of Neurology, International Association of Parkinsonism and related Disorders, all outside the submitted work. CT received fees from ALLERGAN and from MERZ. J-CC reports grants from Sanofi, personal fees from EverPharma, Denali, BrainEver, Theranexus, Air Liquide, all outside the scope of this work. EB reports grants from Medtronic France, Abbvie, UCB, and Aguettant laboratories but no conflict of interest nor financial concerns about the present research paper submitted for publication. AB reports grants from ANR - Agence nationale de recherche, ARNN - Association pour la Recherche en Neuro-imagerie et Neuropsychologie, France Parkinson, AP-HP, FMR - Fondation Maladies Rares (ex GIS), France Parkinson + FRC (Federation pour la Recherche sur le Cerveau), Universite Mohammed V - Rabat, Prix Allianz Institut de France, RDS (Roger de Spoelberch Foundation), FDF -Fondation de France-, all outside the submitted work. All other authors have no competing interests to declare. Ethics Approval Statement: Informed consent was obtained from all participants, and genetic studies were approved by local ethics committees (INSERM, CCPPRB du Groupe Hospitalier Pitie-Salpetriere, Paris, France).

Objective:To quantify the effect of genetic factors and generations influencing the age at onset (AAO) in families with frontotemporal lobar dementia (FTD) due to C9ORF72 hexanucleotide repeat expansions and GRN mutations.Methods:We studied 504 affected individuals from 133 families with C9ORF72 repeat expansions and 90 FTD families with mutations in GRN, 2 major genes responsible for FTD and/or amyotrophic lateral sclerosis. Intrafamilial correlations of AAO were analyzed, and variance component methods were used for heritability estimates. Generational effects on hazard rates for AAO were assessed using mixed-effects Cox proportional hazard models.Results:A generational effect influencing AAO was detected in both C9ORF72 and GRN families. Nevertheless, the estimated proportion of AAO variance explained by genetic factors was high in FTD caused by C9ORF72 repeat expansions (44%; p = 1.10e−4), 62% when the AAO of dementia was specifically taken into account (p = 8.10e−5), and to a lesser degree in GRN families (26%; p = 0.17). Intrafamilial correlation analyses revealed a significant level of correlations in C9ORF72 families according to the degree of kinship. A pattern of intrafamilial correlations also suggested potential X-linked modifiers acting on AAO. Nonsignificant correlation values were observed in GRN families.Conclusions:Our results provide original evidence that genetic modifiers strongly influence the AAO in C9ORF72 carriers, while their effects seem to be weaker in GRN families. This constitutes a rational to search for genetic biomarkers, which could help to improve genetic counseling, patient care, and monitoring of therapeutic trials.

Importance Axonal Charcot-Marie-Tooth disease (CMT) is genetically heterogeneous, with 11 genes identified. Axonal CMT has most frequently been associated with mutations in the MFN2 gene (CMT2A). Objectives To describe the clinical and molecular features of CMT2A, to delineate prognostic factors, to understand connections between a certain phenotype and more serious clinical consequences, and to identify interactions among the associated genes. Evidence Review We describe the clinical, molecular, electrophysiological, and additional features of 43 patients with CMT2A. The degree of physical disability was determined by the CMT neuropathy score and adapted to the CMT neuropathy score gradient to evaluate the clinical course. We evaluated all data within the context of the most recent and important publications concerning this issue. Findings Twenty-five patients had early-onset CMT2A and severe functional disability, with 9 being wheelchair bound, and 18 had late-onset disease and a milder phenotype. Optic atrophy, vocal cord palsy, and auditory impairment were observed in 5, 6, and 2 patients, respectively. Among the 24 patients who underwent magnetic resonance imaging of the spinal cord, 6 had evidence of spinal atrophy with or without hydromyelia. In 1 patient, magnetic resonance imaging revealed hydrocephalus. Twenty different MFN2 mutations were identified, and 14 were considered new variants. Their transmission was predominantly autosomal dominant, with vertical transmission in 8 and de novo occurrence in 3. However, we also identified rare types of transmission, especially a germinal mosaicism and an autosomal recessive inheritance. One patient carried a rare variant in the GDAP1 gene and another in the OPA1 gene in association with MFN2 mutation. Conclusions and Relevance Charcot-Marie-Tooth disease type 2A associated with MFN2 mutations is clinically very heterogeneous. Ranging from a mild to a severe form, CMT2A exhibits various types of transmission. Optic atrophy and vocal cord palsy were observed in patients with severe disability and an early-onset form and also in patients with later onset. Hydromyelia and spinal cord atrophy support central nervous system involvement in CMT2A.