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RRM2Bencodes the p53-inducible small subunit (p53R2) of ribonucleotide reductase, a key protein for mitochondrial DNA (mtDNA) synthesis. Pathogenic variants in this gene result in familial mitochondrial disease in adults and children, secondary to a maintenance disorder of mtDNA. This study describes two patients, mother and son, with early-onset chronic progressive external ophthalmoplegia (PEO). Skeletal muscle biopsy from the latter was examined: cytochrome c oxidase (COX)-negative fibres were shown, and molecular studies revealed multiple mtDNA deletions. A next-generation sequencing gene panel for nuclear-encoded mitochondrial maintenance genes identified two unreported heterozygous missense variants (c.514 G > A and c.682 G > A) in the clinically affected son. The clinically affected mother harboured the first variant in homozygous state, and the clinically unaffected father harboured the remaining variant in heterozygous state. In silico analyses predicted both variants as deleterious. Cell culture studies revealed that patients’ skin fibroblasts, but not fibroblasts from healthy controls, responded to nucleoside supplementation with enhanced mtDNA repopulation, thus suggesting an in vitro functional difference in patients’ cells. Our results support the pathogenicity of two novel RRM2Bvariants found in two patients with autosomal recessive PEO with multiple mtDNA deletions inherited with a pseudodominant pattern.

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common myopathies in adults, displaying a progressive, frequently asymmetric involvement of a typical muscles’ pattern. FSHD is associated with epigenetic derepression of the polymorphic D4Z4 repeat on chromosome 4q, leading to DUX4retrogene toxic expression in skeletal muscles. Identifying biomarkers that correlate with disease severity would facilitate clinical management and assess potential FSHD therapeutics’ efficacy. This study purpose was to analyze serum cytokines to identify potential biomarkers in a large cohort of adult patients with FSHD. We retrospectively measured the levels of 20 pro-inflammatory and regulatory cytokines in serafrom 100 genetically confirmed adult FSHD1 patients. Associations between cytokine concentrations and various clinical scores were investigated. We then measured serum and muscle interleukin 6 (IL-6) levels in a validated FSHD-like mouse model, ranging in severity and DUX4 expression. IL-6 was identified as the only cytokine with a concentration correlating with several clinical severity and functional scores, including Clinical Severity Score, Manual Muscle Testing sum score, Brooke and Vignos scores. Further, FSHD patients displayed overall IL-6 levels more than twice high as control, and patients with milder phenotypes exhibited lower IL-6 serum concentration than those with severe muscular weakness. Lastly, an FSHD-like mouse model analysis confirmed that IL-6 levels positively correlate with disease severity and DUX4 expression. Serum IL-6, therefore, shows promise as a serum biomarker of FSHD severity in a large cohort of FSHD1 adult patients.

ObjectiveNeurofilaments are the major scaffolding proteins for the neuronal cytoskeleton, and variants in NEFHhave recently been described to cause axonal Charcot-Marie-Tooth disease type 2CC (CMT2CC).MethodsIn this large observational study, we present phenotype–genotype correlations on 30 affected and 3 asymptomatic mutation carriers from eight families.ResultsThe majority of patients presented in adulthood with motor-predominant and lower limb-predominant symptoms and the average age of onset was 31.0±15.1 years. A prominent feature was the development of proximal weakness early in the course of the disease. The disease progressed rapidly, unlike other Charcot-Marie-Tooth disease (CMT) subtypes, and half of the patients (53%) needed to use a wheelchair on average 24.1 years after symptom onset. Furthermore, 40% of patients had evidence of early ankle plantarflexion weakness, a feature which is observed in only a handful of CMT subtypes. Neurophysiological studies and MRI of the lower limbs confirmed the presence of a non-length-dependent neuropathy in the majority of patients.All families harboured heterozygous frameshift variants in the last exon of NEFH, resulting in a reading frameshift to an alternate open reading frame and the translation of approximately 42 additional amino acids from the 3' untranslated region (3′-UTR).ConclusionsThis phenotype–genotype study highlights the unusual phenotype of CMT2CC, which is more akin to spinal muscular atrophy rather than classic CMT. Furthermore, the study will enable more informative discussions on the natural history of the disease and will aid in NEFHvariant interpretation in the context of the disease’s unique molecular genetics.

BackgroundCongenital nemaline myopathies are rare pathologies characterised by muscle weakness and rod-shaped inclusions in the muscle fibres.MethodsUsing next-generation sequencing, we identified three patients with pathogenic variants in the Troponin T type 1(TNNT1) gene, coding for the troponin T (TNT) skeletal muscle isoform.ResultsThe clinical phenotype was similar in all patients, associating hypotonia, orthopaedic deformities and progressive chronic respiratory failure, leading to early death. The anatomopathological phenotype was characterised by a disproportion in the muscle fibre size, endomysial fibrosis and nemaline rods. Molecular analyses of TNNT1revealed a homozygous deletion of exons 8 and 9 in patient 1; a heterozygous nonsense mutation in exon 9 and retention of part of intron 4 in muscle transcripts in patient 2; and a homozygous, very early nonsense mutation in patient 3.Western blot analyses confirmed the absence of the TNT protein resulting from these mutations.DiscussionThe clinical and anatomopathological presentations of our patients reinforce the homogeneous character of the phenotype associated with recessive TNNT1mutations. Previous studies revealed an impact of recessive variants on the tropomyosin-binding affinity of TNT. We report in our patients a complete loss of TNT protein due to open reading frame disruption or to post-translational degradation of TNT.

Chikungunya virus (CHIKV) is a re-emerging alphavirus that is transmitted to humans by mosquito bites and causes musculoskeletal and joint pain1,2. Despite intensive investigations, the human cellular factors that are critical for CHIKV infection remain unknown, hampering the understanding of viral pathogenesis and the development of anti-CHIKV therapies. Here we identified the four-and-a-half LIM domain protein 1 (FHL1)3as a host factor that is required for CHIKV permissiveness and pathogenesis in humans and mice. Ablation of FHL1 expression results in the inhibition of infection by several CHIKV strains and o’nyong-nyong virus, but not by other alphaviruses and flaviviruses. Conversely, expression of FHL1 promotes CHIKV infection in cells that do not normally express it. FHL1 interacts directly with the hypervariable domain of the nsP3 protein of CHIKV and is essential for the replication of viral RNA. FHL1 is highly expressed in CHIKV-target cells and is particularly abundant in muscles3,4. Dermal fibroblasts and muscle cells derived from patients with Emery–Dreifuss muscular dystrophy that lack functional FHL15are resistant to CHIKV infection. Furthermore,  CHIKV infection  is undetectable in Fhl1-knockout mice. Overall, this study shows that FHL1 is a key factor expressed by the host that enables CHIKV infection and identifies the interaction between nsP3 and FHL1 as a promising target for the development of anti-CHIKV therapies.

Currently only 25–30% of patients with axonal forms of Charcot-Marie-Tooth disease (CMT) receive a genetic diagnosis. We aimed to identify the causative gene of CMT type 2 in 8 non-related French families with a distinct clinical phenotype. We collected clinical, electrophysiological, and laboratory findings and performed genetic analyses in four different French laboratories. Seventy-two patients with autosomal dominant inheritance were identified. The disease usually started in the fourth decade and the clinical picture was dominated by sensory ataxia (80%), neuropathic pain (38%), and length-dependent sensory loss to all modalities. Electrophysiological studies showed a primarily axonal neuropathy, with possible isolated sensory involvement in milder phenotypes. Disease severity varied greatly but the clinical course was generally mild. We identified 2 novel variants in LRSAM1gene: a deletion of 4 amino acids, p.(Gln698_Gln701del), was found in 7 families and a duplication of a neighboring region of 10 amino acids, p.(Pro702_Gln711dup), in the remaining family. A common haplotype of ~450 kb suggesting a founder effect was noted around LRSAM1in 4 families carrying the first variant. LRSAM1 geneencodes for an E3 ubiquitin ligase important for neural functioning. Our results confirm the localization of variants in its catalytic C-terminal RING domain and broaden the phenotypic spectrum of LRSAM1-related neuropathies, including painful and predominantly sensory ataxic forms.

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Interpretation of next-generation sequencing constitutes the main limitation of molecular diagnostics. In diagnosing myopathies and muscular dystrophies, another issue is efficiency in predicting the pathogenicity of variants identified in large genes, especially TTN; current in silicoprediction tools show limitations in predicting and ranking the numerous variants of such genes. We propose a variant-prioritization tool, the MoBiDiCprioritization algorithm(MPA). MPA is based on curated interpretation of data on previously reported variants, biological assumptions, and splice and missense predictors, and is used to prioritize all types of single-nucleotide variants. MPA was validated by comparing its sensitivity and specificity to those of dbNSFP database prediction tools, using a data set composed of DYSF, DMD, LMNA, NEB,and TTNvariants extracted from expert-reviewed and ExAC databases. MPA obtained the best annotation rates for missense and splice variants. As MPA aggregates the results from several predictors, individual predictor errors are counterweighted, improving the sensitivity and specificity of missense and splice variant predictions. We propose a sequential use of MPA, beginning with the selection of variants with higher scores and followed by, in the absence of candidate pathologic variants, consideration of variants with lower scores. We provide scripts and documentation for free academic use and a validated annotation pipeline scaled for panel and exome sequencing to prioritize single-nucleotide variants from a VCF file.

Myopathies and muscular dystrophies (M-MDs) are genetically heterogeneous diseases, with >100 identified genes, including the giant and complex titin (TTN) and nebulin (NEB) genes. Next-generation sequencing technology revolutionized M-MD diagnosis and revealed high frequency of TTNand NEBvariants. We developed a next-generation sequencing diagnostic strategy targeted to the coding sequences of 135 M-MD genes. Comparison of two targeted capture technologies (SeqCap EZ Choice library capture kit and Nextera Rapid Capture Custom Enrichment kit) and of two whole-exome sequencing kits (SureSelect V5 and TruSeq RapidExome capture) revealed best coverage with the SeqCap EZ Choice protocol. A marked decrease in coverage was observed with the other kits, affecting mostly the first exons of genes and the repeated regions of TTNand NEB. Bioinformatics analysis strategy was fine-tuned to achieve optimal detection of variants, including small insertions/deletions (INDELs) and copy number variants (CNVs). Analysis of a cohort of 128 patients allowed the detection of 52 substitutions, 13 INDELs (including a trinucleotide repeat expansion), and 3 CNVs. Two INDELs were localized in the repeated regions of NEB, suggesting that these mutations may be frequent but underestimated. A large deletion was also identified in TTNthat is, to our knowledge, the first published CNV in this gene.

La sclérose latérale amyotrophique (SLA) est une maladie rapidement mortelle dans la plupart des cas et caractérisée par une dégénérescence des motoneurones centraux et périphériques. Son origine est probablement multifactorielle. Elle touche les deux sexes et tous les âges adultes, pour un début moyen à 64ans. Des facteurs génétiques ont été identifiés, mais ils ne rendent compte que de 10 % des cas. De nombreux facteurs de risque environnementaux ont été explorés depuis de nombreuses années et ils concernent à la fois le mode vie du patient mais aussi son exposition à des facteurs pouvant être délétères. Concernant le mode de vie, il a été publié que les patients exerçaient plus souvent la profession de soudeur ou avaient une activité professionnelle exposée aux métaux lourds ou aux solvants. Les activités ou métiers nécessitant une dépense énergétique quotidienne (maçon, sportif, militaire) étaient également associées à un risque accru de maladie. Les patients seraient plus souvent fumeurs que la moyenne et chez eux l’obésité est plus rare. Parmi les facteurs d’exposition, il faut citer en particulier les pesticides, les metalloïdes, les métaux lourds, les champs magnétiques et la cyanotoxine BMAA pour laquelle de nombreux travaux récents ont permis de préciser le cadre pathogène, même une relation de cause à effet entre cette toxine et la SLA n’est pas formellement établie à ce jour. D’autres facteurs semblent à la frontière entre mode de vie et exposition, tels que les cas conjugaux de SLA qui concernent des personnes ayant une vie commune longue et donc une similitude de régime alimentaire, mais aussi qui sont des sujets exposés au même environnement. De nombreuses questions restent posées et à ce jour bien peu de facteurs environnementaux, s’il y en a, font consensus. Qui dit facteur environnemental dit parfois aussi foyer de haute incidence. Certains ont été identifiés en particulier en France et ils sont en cours d’investigation. Un est situé autour de l’étang de Thau, dans l’Hérault et un autre à Bellentre, en Savoie. Dans le cadre d’un projet collaboratif entre les centres de Limoges, Grenoble et Montpellier, un registre des cas de SLA entre 2004 et 2011 a été constitué. Ce registre avait pour but de permettre une recherche de foyers de haute incidence de la SLA avec une méthodologie très rigoureuse. Un autre but était d’explorer mieux l’hypothèse de la BMAA et d’identifier d’autres facteurs. Nous présenterons un aperçu des avancées dans le domaine de ces zones à haute incidence dans notre pays, en comparant leur environnement avec d’autres zones dans le monde.