A previously unreported NARS1 variant causes dominant distal hereditary motor neuropathy in a French family.

BACKGROUND AND AIMS: Pathogenic variants in the NARS1 gene, which encodes for the asparaginyl-tRNA synthetase1 (NARS1) enzyme, were associated with complex central and peripheral nervous system phenotypes. Recently, Charcot-Marie-Tooth (CMT) disease has been linked to heterozygous pathogenic variants in NARS1 in nine patients. Here, we report two brothers and their mother from a French family with distal hereditary motor neuropathy (dHMN) carrying a previously unreported NARS1 variant. METHODS: The NARS1 variant (c.1555G>C; p.(Gly519Arg)) was identified through whole-genome sequencing (WGS) performed on the family members. Clinical findings, nerve conduction studies (NCS), needle electromyography (EMG), and functional assays in yeast complementation assays are reported here. RESULTS: The family members showed symptoms of dHMN, including distal weakness and osteoarticular deformities. They also exhibited brisk reflexes suggestive of upper motor neuron involvement. All patients were able to walk independently at the last follow-up. NCS and EMG confirmed pure motor neuropathy. Functional assays in yeast confirmed a loss-of-function effect of the variant on NARS1 activity. INTERPRETATION: Our findings expand the clinical spectrum of NARS1-associated neuropathies, highlighting the association of NARS1 mutations with dHMN. The benign disease course observed in our patients suggests a slowly progressive phenotype. Further reports could contribute to a more comprehensive understanding of the spectrum of NARS1-associated neuropathies.

Homozygous COQ7 mutation: a new cause of potentially treatable distal hereditary motor neuropathy.

Distal hereditary motor neuropathy represents a group of motor inherited neuropathies leading to distal weakness. We report a family of two brothers and a sister affected by distal hereditary motor neuropathy in whom a homozygous variant c.3G>T (p.1Met?) was identified in the COQ7 gene. This gene encodes a protein required for coenzyme Q10 biosynthesis, a component of the respiratory chain in mitochondria. Mutations of COQ7 were previously associated with severe multi-organ disorders characterized by early childhood onset and developmental delay. Using patient blood samples and fibroblasts derived from a skin biopsy, we investigated the pathogenicity of the variant of unknown significance c.3G>T (p.1Met?) in the COQ7 gene and the effect of coenzyme Q10 supplementation in vitro. We showed that this variation leads to a severe decrease in COQ7 protein levels in the patient's fibroblasts, resulting in a decrease in coenzyme Q10 production and in the accumulation of 6-demethoxycoenzyme Q10, the COQ7 substrate. Interestingly, such accumulation was also found in the patient's plasma. Normal coenzyme Q10 and 6-demethoxycoenzyme Q10 levels were restored in vitro by using the coenzyme Q10 precursor 2,4-dihydroxybenzoic acid, thus bypassing the COQ7 requirement. Coenzyme Q10 biosynthesis deficiency is known to impair the mitochondrial respiratory chain. Seahorse experiments showed that the patient's cells mainly rely on glycolysis to maintain sufficient ATP production. Consistently, the replacement of glucose by galactose in the culture medium of these cells reduced their proliferation rate. Interestingly, normal proliferation was restored by coenzyme Q10 supplementation of the culture medium, suggesting a therapeutic avenue for these patients. Altogether, we have identified the first example of recessive distal hereditary motor neuropathy caused by a homozygous variation in the COQ7 gene, which should thus be included in the gene panels used to diagnose peripheral inherited neuropathies. Furthermore, 6-demethoxycoenzyme Q10 accumulation in the blood can be used to confirm the pathogenic nature of the mutation. Finally, supplementation with coenzyme Q10 or derivatives should be considered to prevent the progression of COQ7-related peripheral inherited neuropathy in diagnosed patients.

CMT2N-causing aminoacylation domain mutants enable Nrp1 interaction with AlaRS.

Through dominant mutations, aminoacyl-tRNA synthetases constitute the largest protein family linked to Charcot-Marie-Tooth disease (CMT). An example is CMT subtype 2N (CMT2N), caused by individual mutations spread out in AlaRS, including three in the aminoacylation domain, thereby suggesting a role for a tRNA-charging defect. However, here we found that two are aminoacylation defective but that the most widely distributed R329H is normal as a purified protein in vitro and in unfractionated patient cell samples. Remarkably, in contrast to wild-type (WT) AlaRS, all three mutant proteins gained the ability to interact with neuropilin 1 (Nrp1), the receptor previously linked to CMT pathogenesis in GlyRS. The aberrant AlaRS-Nrp1 interaction is further confirmed in patient samples carrying the R329H mutation. However, CMT2N mutations outside the aminoacylation domain do not induce the Nrp1 interaction. Detailed biochemical and biophysical investigations, including X-ray crystallography, small-angle X-ray scattering, hydrogen-deuterium exchange (HDX), switchSENSE hydrodynamic diameter determinations, and protease digestions reveal a mutation-induced structural loosening of the aminoacylation domain that correlates with the Nrp1 interaction. The b1b2 domains of Nrp1 are responsible for the interaction with R329H AlaRS. The results suggest Nrp1 is more broadly associated with CMT-associated members of the tRNA synthetase family. Moreover, we revealed a distinct structural loosening effect induced by a mutation in the editing domain and a lack of conformational impact with C-Ala domain mutations, indicating mutations in the same protein may cause neuropathy through different mechanisms. Our results show that, as with other CMT-associated tRNA synthetases, aminoacylation per se is not relevant to the pathology.

The Hexokinase 1 5'-UTR Mutation in Charcot-Marie-Tooth 4G Disease Alters Hexokinase 1 Binding to Voltage-Dependent Anion Channel-1 and Leads to Dysfunctional Mitochondrial Calcium Buffering.

Demyelinating Charcot-Marie-Tooth 4G (CMT4G) results from a recessive mutation in the 5'UTR region of the Hexokinase 1 (HK1) gene. HK participates in mitochondrial calcium homeostasis by binding to the Voltage-Dependent Anion Channel (VDAC), through its N-terminal porin-binding domain. Our hypothesis is that CMT4G mutation results in a broken interaction between mutant HK1 and VDAC, disturbing mitochondrial calcium homeostasis. We studied a cohort of 25 CMT4G patients recruited in the French gypsy population. The disease was characterized by a childhood onset, an intermediate demyelinating pattern, and a significant phenotype leading to becoming wheelchair-bound by the fifth decade of life. Co-IP and PLA studies indicated a strong decreased interaction between VDAC and HK1 in the patients' PBMCs and sural nerve. We observed that either wild-type HK1 expression or a peptide comprising the 15 aa of the N-terminal wild-type HK1 administration decreased mitochondrial calcium release in HEK293 cells. However, mutated CMT4G HK1 or the 15 aa of the mutated HK1 was unable to block mitochondrial calcium release. Taken together, these data show that the CMT4G-induced modification of the HK1 N-terminus disrupts HK1-VDAC interaction. This alters mitochondrial calcium buffering that has been shown to be critical for myelin sheath maintenance.

Clinical and electrophysiological characteristics of women with X-linked Charcot-Marie-Tooth disease.

BACKGROUND: X-Linked Charcot-Marie-Tooth disease type 1 (CMTX1) is characterized by gender differences in clinical severity. Women are usually clinically affected later and less severely than men. However, their clinical presentation appears to be heterogenous. Our aim was to extend the phenotypic description in a large series of women with CMTX1. METHODS: We retrospectively evaluated 263 patients with CMTX1 from 11 French reference centers. Demographic, clinical, and nerve conduction data were collected. The severity was assessed by CMT Examination Score (CMTES) and Overall Neuropathy Limitations Scale (ONLS) scores. We looked for asymmetrical strength, heterogeneous motor nerve conduction velocity (MNCV), and motor conduction blocks (CB). RESULTS: The study included 137 women and 126 men from 151 families. Women had significantly more asymmetric motor deficits and MNCV than men. Women with an age of onset after 19 years were milder. Two groups of women were identified after 48 years of age. The first group represented 55%, with women progressing as severely as men, however, with a later onset age. The second group had mild or no symptoms. Some 39% of women had motor CB. Four women received intravenous immunoglobulin before being diagnosed with CMTX1. CONCLUSIONS: We identified two subgroups of women with CMTX1 who were over 48 years of age. Additionally, we have demonstrated that women with CMTX can exhibit an atypical clinical presentation, which may result in misdiagnosis. Therefore, in women presenting with chronic neuropathy, the presence of clinical asymmetry, heterogeneous MNCV, and/or motor CB should raise suspicion for X-linked CMT, particularly CMTX1, and be included in the differential diagnosis.

SORD-related peripheral neuropathy in a French and Swiss cohort: Clinical features, genetic analyses, and sorbitol dosages.

BACKGROUND AND PURPOSE: Biallelic variants in SORD have been reported as one of the main recessive causes for hereditary peripheral neuropathies such as Charcot-Marie-Tooth disease type 2 (CMT2) and distal hereditary motor neuropathy (dHMN) resulting in lower limb (LL) weakness and muscular atrophy. In this study, phenotype and genotype landscapes of SORD-related peripheral neuropathies were described in a French and Swiss cohort. Serum sorbitol dosages were used to classify SORD variants. METHODS: Patients followed at neuromuscular reference centres in France and Switzerland were ascertained. Sanger sequencing and next generation sequencing were performed to sequence SORD, and mass spectrometry was used to measure patients' serum sorbitol. RESULTS: Thirty patients had SORD peripheral neuropathy associating LL weakness with muscular atrophy, foot deformities (87%), and sometimes proximal LL weakness (20%) or distal upper limb weakness (50%). Eighteen had dHMN, nine had CMT2, and three had intermediate CMT. Most of them had a mild or moderate disease severity. Sixteen carried a homozygous c.757delG (p.Ala253Glnfs*27) variant, and 11 carried compound heterozygous variants, among which four variants were not yet reported: c.403C > G, c.379G > A, c.68_100 + 1dup, and c.850dup. Two unrelated patients with different origins carried a homozygous c.458C > A variant, and one patient carried a new homozygous c.786 + 5G > A variant. Mean serum sorbitol levels were 17.01 mg/L ± 8.9 SD for patients carrying SORD variants. CONCLUSIONS: This SORD-inherited peripheral neuropathy cohort of 30 patients showed homogeneous clinical presentation and systematically elevated sorbitol levels (22-fold) compared to controls, with both diagnostic and potential therapeutic implications.

Phenotypic spectrum and genomics of undiagnosed arthrogryposis multiplex congenita.

BACKGROUND: Arthrogryposis multiplex congenita (AMC) is characterised by congenital joint contractures in two or more body areas. AMC exhibits wide phenotypic and genetic heterogeneity. Our goals were to improve the genetic diagnosis rates of AMC, to evaluate the added value of whole exome sequencing (WES) compared with targeted exome sequencing (TES) and to identify new genes in 315 unrelated undiagnosed AMC families. METHODS: Several genomic approaches were used including genetic mapping of disease loci in multiplex or consanguineous families, TES then WES. Sanger sequencing was performed to identify or validate variants. RESULTS: We achieved disease gene identification in 52.7% of AMC index patients including nine recently identified genes (CNTNAP1, MAGEL2, ADGRG6, ADCY6, GLDN, LGI4, LMOD3, UNC50 and SCN1A). Moreover, we identified pathogenic variants in ASXL3 and STAC3 expanding the phenotypes associated with these genes. The most frequent cause of AMC was a primary involvement of skeletal muscle (40%) followed by brain (22%). The most frequent mode of inheritance is autosomal recessive (66.3% of patients). In sporadic patients born to non-consanguineous parents (n=60), de novo dominant autosomal or X linked variants were observed in 30 of them (50%). CONCLUSION: New genes recently identified in AMC represent 21% of causing genes in our cohort. A high proportion of de novo variants were observed indicating that this mechanism plays a prominent part in this developmental disease. Our data showed the added value of WES when compared with TES due to the larger clinical spectrum of some disease genes than initially described and the identification of novel genes.

Expanding the phenotypic variability of MORC2 gene mutations: From Charcot-Marie-Tooth disease to late-onset pure motor neuropathy.

MORC2 gene encodes a ubiquitously expressed nuclear protein involved in chromatin remodeling, DNA repair, and transcriptional regulation. Heterozygous mutations in MORC2 gene have been associated with a spectrum of disorders affecting the peripheral nervous system such as Charcot-Marie-Tooth (CMT2Z), spinal muscular atrophy-like with or without cerebellar involvement, and a developmental syndrome associated with impaired growth, craniofacial dysmorphism and axonal neuropathy (DIGFAN syndrome). Such variability in clinical manifestations associated with the increasing number of variants of unknown significance detected by next-generation sequencing constitutes a serious diagnostic challenge. Here we report the characterization of an in vitro model to evaluate the pathogenicity of variants of unknown significance based on MORC2 overexpression in a neuroblastoma cell line SH-EP or cortical neurons. Likewise, we show that MORC2 mutants affect survival and trigger apoptosis over time in SH-EP cell line. Furthermore, overexpression in primary cortical neurons increases apoptotic cell death and decreases neurite outgrowth. Altogether, these approaches establish the pathogenicity of two new variants p.Gly444Arg and p.His446Gln in three patients from two families. These new mutations in MORC2 gene are associated with autosomal dominant CMT and with adult late onset proximal motor neuropathy, further increasing the spectrum of clinical manifestations associated with MORC2 mutations.

HINT1 neuropathy: Expanding the genotype and phenotype spectrum.

Inherited peripheral neuropathy (IPN) is a heterogeneous group of disorders due to pathogenic variation in more than 100 genes. In 2012, the first cases of IPN associated with HINT1 pathogenic variations were described in 33 families sharing the same phenotype characterized by an axonal neuropathy with neuromyotonia and autosomal recessive inheritance (NMAN: OMIM #137200). Histidine Triad Nucleotide Binding Protein 1 regulates transcription, cell-cycle control, and is possibly involved in neuropsychiatric pathophysiology. Herein, we report seven French patients with NMAN identified by Next Generation Sequencing. We conducted a literature review and compared phenotypic and genotypic features with our cohort. We identified a new HINT1 pathogenic variation involved in NMAN: c.310G>C p.(Gly104Arg). This cohort is comparable with literature data regarding age of onset (7,4yo), neuronal involvement (sensorimotor 3/7 and motor pure 4/7), and skeletal abnormalities (scoliosis 3/7, feet anomalies 6/7). We expand the phenotypic spectrum of HINT1-related neuropathy by describing neurodevelopmental or psychiatric features in six out of seven individuals such as generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), mood disorder and attention deficit hyperactivity disorder (ADHD). However, only 3/128 previously described patients had neuropsychiatric symptomatology or neurodevelopmental disorder. These features could be part of HINT1-related disease, and we should further study the clinical phenotype of the patients.

Charcot-Marie-Tooth disease type 2CC due to NEFH variants causes a progressive, non-length-dependent, motor-predominant phenotype.

OBJECTIVE: Neurofilaments are the major scaffolding proteins for the neuronal cytoskeleton, and variants in NEFH have recently been described to cause axonal Charcot-Marie-Tooth disease type 2CC (CMT2CC). METHODS: In this large observational study, we present phenotype-genotype correlations on 30 affected and 3 asymptomatic mutation carriers from eight families. RESULTS: The 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). CONCLUSIONS: This 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 NEFH variant interpretation in the context of the disease's unique molecular genetics.

Unexpected Intermediate Nerve Conduction Velocity Findings in Charcot-Marie-Tooth Syndromes Classified as Demyelinated or Axonal in a Pediatric Population.

INTRODUCTION: Among the hereditary motor and sensory neuropathies (HMSN), demyelinating forms are the best characterized, with a clear predominance of CMT1A. The axonal and intermediate forms are less described. The aim of this study is to report the genetic diagnosis of Charcot-Marie-Tooth (CMT) according to the nerve conduction velocity (NCV) findings in a pediatric population. METHODS: We retrospectively described a population of HMSN children with a confirmed genetic diagnosis of demyelinated, intermediate, or axonal forms. We compared the results of the genetic analyses with those of motor NCV in median nerve according to whether they were below 25 m/s (demyelinating group); between 25 and 45 m/s (intermediate group), or above 45 m/s (axonal group). RESULTS: Among the 143 children with an HMSN, 107 had a genetic diagnosis of which 61 had an electromyogram. On NCV findings: seven (11%) pertain to the axonal group, 20 (32%) to the intermediate group, and 34 (55%) to the demyelinating group. When NCV was above 45 m/s, CMT2A was the predominant genetic diagnosis (70%) when NCV were below 25 m/s, CMT1A was the predominant genetic diagnosis (71%). Intermediate NCV findings group was the more heterogeneous with seven genetic CMT subgroups (60% CMT1A, CMT1B, CMT1X, CMT2A, CMT2N, CMT4G). CONCLUSION: Taking NCV values between 25 and 45 m/s to define an intermediate group of CMT in children leads to the inclusion of non-typically "intermediate", especially CMT1A. We emphasize the broad spectrum of NCV in CMT1A that justified the systematic search of PMP22 duplication/deletion screening before next generation sequencing panel.

Charcot-Marie-Tooth disease misdiagnosed as chronic inflammatory demyelinating polyradiculoneuropathy: An international multicentric retrospective study.

BACKGROUND AND PURPOSE: Charcot-Marie-Tooth (CMT) disease, an untreatable hereditary polyneuropathy, may mimic chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), a treatable neuropathy. METHODS: In this retrospective study, we analyzed the characteristics of CMT patients misdiagnosed as CIDP at 16 university hospitals in three countries, compared these patients with a reference group of CIDP patients, and estimated the cost of misdiagnosis. RESULTS: Among 1104 CIDP cases, we identified 35 CMT patients misdiagnosed as CIDP (3.2%). All were initially diagnosed with definite or probable CIDP (European Federation of Neurological Societies/Peripheral Nerve Society criteria), and mutations in PMP22, MPZ, and 10 other CMT genes were found in 34%, 31%, and 35% of cases, respectively. In comparison with a reference group of 35 CIDP patients, CMT patients were younger (median age at disease onset = 39 vs. 56 years) and more frequently had motor weakness at disease onset (80% vs. 29%), hearing loss (14% vs. 0%), normal brachial plexus imaging (70% vs. 40%), lower cerebrospinal fluid protein content (median = 0.5 vs. 0.8 g/L), and lower treatment response (20% vs. 69%). Treatment cost in these 35 misdiagnosed patients was estimated at 4.6 million euros (M€), whereas the cost of CMT genetic analysis in 1104 patients was estimated at 2.7 M€. CONCLUSIONS: In this study, 35 of 1104 (3.2%) patients initially diagnosed with CIDP had CMT. Importantly, the cost of treating these 35 misdiagnosed patients was significantly higher than the cost of performing CMT genetic analysis in 1104 patients (4.6 M€ vs. 2.7 M€), suggesting that CMT genetic investigations should be more widely used before diagnosing CIDP.

Giant axonal neuropathy: a multicenter retrospective study with genotypic spectrum expansion.

Giant axonal neuropathy (GAN) is an autosomal recessive disease caused by mutations in the GAN gene encoding gigaxonin. Patients develop a progressive sensorimotor neuropathy affecting peripheral nervous system (PNS) and central nervous system (CNS). Methods: In this multicenter observational retrospective study, we recorded French patients with GAN mutations, and 10 patients were identified. Mean age of patients was 9.7 years (2-18), eight patients were female (80%), and all patients met infant developmental milestones and had a family history of consanguinity. Mean age at disease onset was 3.3 years (1-5), and progressive cerebellar ataxia and distal motor weakness were the initial symptoms in all cases. Proximal motor weakness and bulbar symptoms appeared at a mean age of 12 years (8-14), and patients used a wheelchair at a mean age of 16 years (14-18). One patient died at age 18 years from aspiration pneumonia. In all cases, nerve conduction studies showed a mixed demyelinating and axonal sensorimotor neuropathy and MRI showed brain and cerebellum white matter abnormalities. Polyneuropathy and encephalopathy both aggravated during the course of the disease. Patients also showed a variety of associated findings, including curly hair (100% of cases), pes cavus (80%), ophthalmic abnormalities (30%), and scoliosis (30%). Five new GAN mutations were found, including the first synonymous mutation and a large intragenic deletion. Our findings expand the genotypic spectrum of GAN mutations, with relevant implications for molecular analysis of this gene, and confirm that GAN is an age-related progressive neurodegenerative disease involving PNS and CNS.

A multicenter retrospective study of charcot-marie-tooth disease type 4B (CMT4B) associated with mutations in myotubularin-related proteins (MTMRs).

OBJECTIVE: Charcot-Marie-Tooth (CMT) disease 4B1 and 4B2 (CMT4B1/B2) are characterized by recessive inheritance, early onset, severe course, slowed nerve conduction, and myelin outfoldings. CMT4B3 shows a more heterogeneous phenotype. All are associated with myotubularin-related protein (MTMR) mutations. We conducted a multicenter, retrospective study to better characterize CMT4B. METHODS: We collected clinical and genetic data from CMT4B subjects in 18 centers using a predefined minimal data set including Medical Research Council (MRC) scores of nine muscle pairs and CMT Neuropathy Score. RESULTS: There were 50 patients, 21 of whom never reported before, carrying 44 mutations, of which 21 were novel and six representing novel disease associations of known rare variants. CMT4B1 patients had significantly more-severe disease than CMT4B2, with earlier onset, more-frequent motor milestones delay, wheelchair use, and respiratory involvement as well as worse MRC scores and motor CMT Examination Score components despite younger age at examination. Vocal cord involvement was common in both subtypes, whereas glaucoma occurred in CMT4B2 only. Nerve conduction velocities were similarly slowed in both subtypes. Regression analyses showed that disease severity is significantly associated with age in CMT4B1. Slopes are steeper for CMT4B1, indicating faster disease progression. Almost none of the mutations in the MTMR2 and MTMR13 genes, responsible for CMT4B1 and B2, respectively, influence the correlation between disease severity and age, in agreement with the hypothesis of a complete loss of function of MTMR2/13 proteins for such mutations. INTERPRETATION: This is the largest CMT4B series ever reported, demonstrating that CMT4B1 is significantly more severe than CMT4B2, and allowing an estimate of prognosis. ANN NEUROL 2019.

A cryptic splicing mutation in the INF2 gene causing Charcot-Marie-Tooth disease with minimal glomerular dysfunction.

Heterozygous mutations in the inverted formin-2 (INF2) gene provoke focal segmental glomerulosclerosis (FSGS) and intermediate Charcot-Marie-Tooth (CMT) disease with FSGS. Here, we report four patients from a three-generation family with a new cryptic splicing INF2 mutation causing autosomal dominant intermediate CMT with minimal glomerular dysfunction. Three males and one female with a mean age of 51 years (26-87) presented with a slowly progressive sensorimotor polyneuropathy, pes cavus, and kyphoscoliosis. Mean age at CMT disease onset was 11.5 years (3-17), and electrophysiological studies showed demyelinating and axonal features consistent with intermediate CMT. Plasma albumin and creatinine were normal in all four cases, and urine protein was normal in one case and mildly raised in three patients (mean: 0.32 g/L [0.18-0.44], N < 0.14). Genetic analysis found a c.271C > G (p. Arg91Gly) variation in INF2 exon 2, and in vitro splicing assays showed the deletion of the last 120 nucleotides of INF2 exon 2 leading to a 40 amino acids in-frame deletion (p. Arg91_p. Gln130del). This report expands the genetic spectrum of INF2-associated disorders and demonstrates that INF2 mutations may provoke isolated CMT with no clinically relevant kidney involvement. Consequently, INF2 mutation analysis should not be restricted to individuals with coincident neuropathy and renal disease.

A novel pathogenic variant of NEFL responsible for deafness associated with peripheral neuropathy discovered through next-generation sequencing and review of the literature.

Neurofilaments are neuron-specific intermediate filaments essential for the radial growth of axons during development and the maintenance of axonal diameter. Pathogenic variants of Neurofilament Light (NEFL) are associated with CMT1F, CMT2E, and CMTDIG and have been observed in less than 1% of Charcot-Marie-Tooth (CMT) cases, resulting in the reporting of 35 variants in 173 CMT patients to date. However, only six variants have been reported in 17 patients with impaired hearing. No genotype-phenotype correlations have yet been established. Here, we report an additional case: a 69-year-old female, who originally presented with axonal sensory and motor neuropathy at the age of 45, associated with moderate sensorineural hearing loss, with a slight slope at high frequencies. Next-generation sequencing identified a novel pathogenic variant: c.269A > G, p.(Glu90Gly). Hearing impairment is often linked to CMT due to pathogenic variants of NEFL, especially p.(Glu90Lys) and p.(Asn98Ser), and in our case p.(Glu90Gly). These pathogenic variants are all located at hot spots, in the head domain and the two ends of the rod domain of the protein.

WES homozygosity mapping in a recessive form of Charcot-Marie-Tooth neuropathy reveals intronic GDAP1 variant leading to a premature stop codon.

Charcot-Marie-Tooth disease (CMT) refers to a group of clinically and genetically heterogeneous inherited neuropathies. Ganglioside-induced differentiation-associated protein 1 GDAP1-related CMT has been reported in an autosomal dominant or recessive form in patients presenting either axonal or demyelinating neuropathy. We report two Sri Lankan sisters born to consanguineous parents and presenting with a severe axonal sensorimotor neuropathy. The early onset of the disease, the distal and proximal weakness and atrophy leading to major disability, along with areflexia, and, most notably, vocal cord and diaphragm paralysis were highly evocative of a GDAP1-related CMT. However, sequencing of the coding regions of the gene was normal. Whole-exome sequencing (WES) was performed and revealed that the largest region of homozygosity was around GDAP1 with several variants, mostly in non-coding regions. In view of the high clinical suspicion of GDAP1 gene involvement, we examined the variants in this gene and this, along with functional studies, allowed us to identify an alternative splicing site revealing a cryptic in-frame stop codon in intron 4 responsible for a severe loss of wild-type GDAP1. This work is the first to describe a deleterious mutation in GDAP1 gene outside of coding sequences or intronic junctions and emphasizes the importance of interpreting molecular analysis, and in particular WES results, in light of the clinical and electrophysiological phenotype.

Contribution of tandem mass spectrometry to the diagnosis of lysosomal storage disorders.

Tandem mass spectrometry (MS/MS) is a highly sensitive and specific technique. Thanks to the development of triple quadrupole analyzers, it is becoming more widely used in laboratories working in the field of inborn errors of metabolism. We review here the state of the art of this technique applied to the diagnosis of lysosomal storage disorders (LSDs) and how MS/MS has changed the diagnostic rationale in recent years. This fine technology brings more sensitive, specific, and reliable methods than the previous biochemical ones for the analysis of urinary glycosaminoglycans, oligosaccharides, and sialic acid. In sphingolipidoses, the quantification of urinary sphingolipids (globotriaosylceramide, sulfatides) is possible. The measurement of new plasmatic biomarkers such as oxysterols, bile acids, and lysosphingolipids allows the screening of many sphingolipidoses and related disorders (Niemann-Pick type C), replacing tedious biochemical techniques. Applied to amniotic fluid, a more reliable prenatal diagnosis or screening of LSDs is now available for fetuses presenting with antenatal manifestations. Applied to enzyme measurements, it allows high throughput assays for the screening of large populations, even newborn screening. The advent of this new method can modify the diagnostic rationale behind LSDs.

C9orf72 Protein Plasmatic Concentrations Are Similar between C9ORF72 Expansion Carriers and Noncarriers in Frontotemporal Dementia.

BACKGROUND/AIMS: The aim of the study was to assess the theory of haploinsufficiency in C9ORF72 expansion carriers, the most frequent causative gene of frontotemporal dementia. METHODS: Plasmatic concentrations of C9orf72 protein were measured in 33 patients suspected of familial frontotemporal dementia using an enzyme-linked immunosorbent assay. RESULTS: No difference was observed between C9ORF72 expansion carriers (21.2% of patients) and noncarriers (78.8% of patients). C9orf72 protein determination is not a suitable biomarker for screening C9ORF72 expansion carriers. CONCLUSION: Our results provide new evidence against the hypothesis of haploinsufficiency leading to frontotemporal dementia in C9ORF72 expansion carriers.