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.

EGR2 gene-linked hereditary neuropathies present with a bimodal age distribution at symptoms onset.

BACKGROUND: Mutations in the Early-Growth Response 2 (EGR2) gene cause various hereditary neuropathies, including demyelinating Charcot-Marie-Tooth (CMT) disease type 1D (CMT1D), congenital hypomyelinating neuropathy type 1 (CHN1), Déjerine-Sottas syndrome (DSS), and axonal CMT (CMT2). METHODS: In this study, we identified 14 patients with heterozygous EGR2 mutations diagnosed between 2000 and 2022. RESULTS: Mean age was 44 years (15-70), 10 patients were female (71%), and mean disease duration was 28 years (1-56). Disease onset was before age 15 years in nine cases (64%), after age 35 years in four cases (28%), and one patient aged 26 years was asymptomatic (7%). All symptomatic patients had pes cavus and distal lower limbs weakness (100%). Distal lower limbs sensory symptoms were observed in 86% of cases, hand atrophy in 71%, and scoliosis in 21%. Nerve conduction studies showed a predominantly demyelinating sensorimotor neuropathy in all cases (100%), and five patients needed walking assistance after a mean disease duration of 50 years (47-56) (36%). Three patients were misdiagnosed as inflammatory neuropathy and treated with immunosuppressive drugs for years before diagnosis was corrected. Two patients presented with an additional neurologic disorder, including Steinert's myotonic dystrophy and spinocerebellar ataxia (14%). Eight EGR2 gene mutations were found, including four previously undescribed. INTERPRETATION: Our findings demonstrate EGR2 gene-related hereditary neuropathies are rare and slowly progressive demyelinating neuropathies with two major clinical presentations, including a childhood-onset variant and an adult-onset variant which may mimic inflammatory neuropathy. Our study also expands the genotypic spectrum of EGR2 gene mutations.

[Treating hereditary neuropathies : a dream come true?] / Traiter les neuropathies héréditaires : un rêve qui devient réalité ?

Hereditary neuropathies have been the subject of recent major therapeutic advances. Treatments based on antisense oligonucleotides (ASO) and small interfering RNA (siRNA) have been developed and are now commercially available to treat hereditary transthyretin amyloidosis (hTTR) and porphyria. More recently, a CRISPR-Cas9 genomic editing treatment targeting the TTR gene has been developed and is being tested in patients with hTTR. Based on their success in hTTR and porphyria, innovative treatments targeting mRNA and DNA are being evaluated in other hereditary neuropathies, including Charcot-Marie-Tooth disease (CMT).

Les neuropathies héréditaires ont fait l'objet d'avancées thérapeu­tiques majeures. Ainsi, des traitements à base d'oligonucléotides antisens (ASO) et d'ARN interférentiels (ARNi) ont récemment été développés et sont maintenant disponibles pour traiter efficacement la neuropathie amyloïde familiale à transthyrétine (NAF-TTR) et la porphyrie. Encore plus récemment, des traitements d'édition génomique de type CRISPR-Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats-Cas9) ciblant le gène TTR ont été mis au point et sont testés chez des patients avec une NAF-TTR. Forts de leur succès dans la NAF-TTR et la porphyrie, ces traitements innovants ciblant l'ARNm et l'ADN sont en cours d'évaluation dans d'autres neuropathies héréditaires, dont la maladie de Charcot-Marie-Tooth (CMT).

Genotype-phenotype correlation in French patients with myelin protein zero gene-related inherited neuropathy.

BACKGROUND AND PURPOSE: Preparations for clinical trials of unfolded protein response (UPR) inhibitors (such as Sephin1) that target the upregulated UPR in patients with Charcot-Marie-Tooth disease (CMT) carrying MPZ mutations are currently underway. The inclusion criteria for these trials are still being formulated. Our objective was to characterize the relation between genotypes and phenotypes in patients with CMT caused by MPZ mutations, and to refine the inclusion criteria for future trials. METHODS: Clinical and neurophysiological data of CMT patients with MPZ mutations were retrospectively collected at 11 French reference centers. RESULTS: Forty-four mutations in MPZ were identified in 91 patients from 61 families. There was considerable heterogeneity. The same mutation was found to cause either axonal or demyelinating neuropathy. Three groups were identified according to the age at disease onset. CMT Examination Score (CMTES) tended to be higher in the early (≤22 years) and adult (23-47 years) onset groups (mean CMTESv2 = 10.4 and 10.0, respectively) than in the late onset group (>47 years, mean CMTESv2 = 8.6, p = 0.47). There was a significant positive correlation between CMTESv2 and the age of patients in Groups I (p = 0.027) and II (p = 0.023), indicating that clinical severity progressed with age in these patients. CONCLUSIONS: To optimize the selection of CMT patients carrying MPZ mutations for the upcoming trials, inclusion criteria should take into account the pathophysiology of the disease (upregulated UPR). Recruited patients should have a mild to moderate disease severity and a disease onset at between 18 and 50 years, as these patients exhibit significant disease progression over time.

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.

Phosphoglycerate kinase deficiency: A nationwide multicenter retrospective study.

Phosphoglycerate kinase (PGK) deficiency is a rare X-linked metabolic disorder caused by mutations in the PGK1 gene. Patients usually develop various combinations of nonspherocytic hemolytic anemia (NSHA), myopathy, and central nervous system disorders. In this national multicenter observational retrospective study, we recorded all known French patients with PGK deficiency, and 3 unrelated patients were identified. Case 1 was a 32-year-old patient with severe chronic axonal sensorimotor polyneuropathy resembling Charcot-Marie-Tooth (CMT) disease, mental retardation, microcephaly, ophthalmoplegia, pes cavus, and the new c.323G > A PGK1 hemizygous mutation. Case 2 was a 71-year-old patient with recurrent exertional rhabdomyolysis, and a c.943G > A PGK1 hemizygous mutation. Case 3 was a 48-year-old patient with NSHA, retinitis pigmentosa, mental retardation, seizures, stroke, parkinsonism, and a c.491A > T PGK1 hemizygous mutation. This study confirms that PGK deficiency is an extremely rare disorder with a wide phenotypic spectrum, and demonstrates for the first time that PGK deficiency may affect the peripheral nervous system and present as a CMT-like disorder.

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.

Novel insights in the disease biology of mutant small heat shock proteins in neuromuscular diseases.

Small heat shock proteins are molecular chaperones that exert diverse cellular functions. To date, mutations in the coding regions of HSPB1 (Hsp27) and HSPB8 (Hsp22) were reported to cause distal hereditary motor neuropathy and Charcot-Marie-Tooth disease. Recently, the clinical spectrum of HSPB1 and HSPB8 mutations was expanded to also include myopathies. Here we provide an update on the molecular genetics and biology of small heat shock protein mutations in neuromuscular diseases.

Increased mitochondrial fusion in a autosomal recessive CMT2A family with mitochondrial GTPase mitofusin 2 mutations.

Charcot-Marie-Tooth type 2A disease (CMT2A) is an inherited peripheral neuropathy mainly caused by mutations in the MFN2 gene coding for the mitochondrial fusion protein mitofusin 2. Although the disease is mainly inherited in a dominant fashion, few cases of early-onset autosomal recessive CMT2A (AR-CMT2A) have been reported in recent years. In this study, we characterized the structure of the mitochondrial network in cultured primary fibroblasts obtained from AR-CMT2A family members. The patient-derived cells showed an increase of the mitochondrial fusion with large connected networks and an increase of the mitochondrial volume. Interestingly, fibroblasts derived from the two asymptomatic parents showed similar changes to a lesser extent. These results support the hypothesis that AR-CMT2A-related MFN2 mutations acts through a semi-dominant negative mechanism and suggest that other biological parameters might show mild alterations in asymptomatic heterozygote AR-CMT2A patients. Such alterations could be useful biomarkers helping to distinguish MFN2 mutations from variants, a growing challenge with the advent of next generation sequencing into routine clinical practice.

Central nervous system abnormalities in patients with PMP22 gene mutations: a prospective study.

BACKGROUND: Mutations of the peripheral myelin protein-22 (PMP22) gene are the most common cause of inherited disease of the peripheral nervous system (PNS), with its deletion resulting in hereditary neuropathy with liability to pressure palsies (HNPP), and its duplication inducing Charcot-Marie-Tooth 1A (CMT1A) disease. Although mainly expressed in the PNS, PMP22 mRNA and protein are also present in the central nervous system (CNS). OBJECTIVE: To investigate whether patients with PMP22 mutations present with CNS abnormalities. METHODS: Fifteen patients with HNPP and 15 patients with CMT1A disease were prospectively included and their brain MRI and neuropsychological assessment were compared with those of healthy subjects. We evaluated, in particular, the volumes of grey and white matter (GM and WM) and looked for metabolic changes using spectroscopy, and abnormal architecture using fractional anisotropy (FA) measurement. A post mortem examination of the CNS of a patient with PMP22 gene duplication was also performed. RESULTS: We found a decrease in the volume of WM in 70% of patients, a reduced creatine level in WM in 28% and a cognitive impairment in 70%. FA was significantly altered in several areas of WM, including the columns of the fornix. The results for WM volume, creatine level in WM and cognitive testing showed that 47% of patients (patients with HNPP and those with CMT1A) presented with at least two abnormal results. Pathological examination of the brain of a patient with PMP22 gene duplication showed diffuse hypomyelination sparing the U fibres. CONCLUSIONS: This study demonstrates that altered PMP22 gene expression induces significant CNS alterations in patients with HNPP and CMT1A, including cerebral WM abnormalities and cognitive impairment.

Mutation spectrum in the large GTPase dynamin 2, and genotype-phenotype correlation in autosomal dominant centronuclear myopathy.

Centronuclear myopathy (CNM) is a genetically heterogeneous disorder associated with general skeletal muscle weakness, type I fiber predominance and atrophy, and abnormally centralized nuclei. Autosomal dominant CNM is due to mutations in the large GTPase dynamin 2 (DNM2), a mechanochemical enzyme regulating cytoskeleton and membrane trafficking in cells. To date, 40 families with CNM-related DNM2 mutations have been described, and here we report 60 additional families encompassing a broad genotypic and phenotypic spectrum. In total, 18 different mutations are reported in 100 families and our cohort harbors nine known and four new mutations, including the first splice-site mutation. Genotype-phenotype correlation hypotheses are drawn from the published and new data, and allow an efficient screening strategy for molecular diagnosis. In addition to CNM, dissimilar DNM2 mutations are associated with Charcot-Marie-Tooth (CMT) peripheral neuropathy (CMTD1B and CMT2M), suggesting a tissue-specific impact of the mutations. In this study, we discuss the possible clinical overlap of CNM and CMT, and the biological significance of the respective mutations based on the known functions of dynamin 2 and its protein structure. Defects in membrane trafficking due to DNM2 mutations potentially represent a common pathological mechanism in CNM and CMT.

Characteristics of clinical and electrophysiological pattern of Charcot-Marie-Tooth 4C.

To describe the clinical and electrophysiological features evoking CMT4C, an autosomal recessive (AR) form of Charcot-Marie-Tooth disease (CMT) due to mutations in the SH3TC2 gene, we screened the coding sequence of SH3TC2 gene in 102 unrelated patients with a demyelinating or intermediate CMT and a family history compatible with an AR transmission. We identified among this cohort 16 patients carrying two mutations in the SH3TC2 gene, but medical records finally analyzed 14 patients. We report clinical, electrophysiological, and molecular data of 14 patients (9 men, 5 women) with CMT4C. Mean age at examination was 43.6 years (median = 42.5). Among the 14 studied cases 6 had scoliosis as the presenting sign. Cranial nerve involvement affecting either the VIIIth, VIIth, XIIth or a combination of the IXth and Xth nerves was noted in 10 patients. Remarkably, 50% of the patients had proximal limb involvement at the time of examination. The hallmark of the electrophysiological study was the presence of probable conduction block and temporal dispersion. Thus the clinical and paraclinical spectrum of CMT4C can guide the clinician to perform analysis of the SH3TC2 gene.

Treating PMP22 gene duplication-related Charcot-Marie-Tooth disease: the past, the present and the future.

Charcot-Marie-Tooth (CMT) disease is the most frequent inherited neuropathy, affecting 1/1500 to 1/10000. CMT1A represents 60%-70% of all CMT and is caused by a duplication on chromosome 17p11.2 leading to an overexpression of the Peripheral Myelin Protein 22 (PMP22). PMP22 gene is under tight regulation and small changes in its expression influences myelination and affect motor and sensory functions. To date, CMT1A treatment is symptomatic and classic pharmacological options have been disappointing. Here, we review the past, present, and future treatment options for CMT1A, with a special emphasis on the highly promising potential of PMP22-targeted small interfering RNA and antisense oligonucleotides.

Squalenoyl siRNA PMP22 nanoparticles are effective in treating mouse models of Charcot-Marie-Tooth disease type 1 A.

Charcot-Marie-Tooth disease type 1 A (CMT1A) lacks an effective treatment. We provide a therapy for CMT1A, based on siRNA conjugated to squalene nanoparticles (siRNA PMP22-SQ NPs). Their administration resulted in normalization of Pmp22 protein levels, restored locomotor activity and electrophysiological parameters in two transgenic CMT1A mouse models with different severity of the disease. Pathological studies demonstrated the regeneration of myelinated axons and myelin compaction, one major step in restoring function of myelin sheaths. The normalization of sciatic nerve Krox20, Sox10 and neurofilament levels reflected the regeneration of both myelin and axons. Importantly, the positive effects of siRNA PMP22-SQ NPs lasted for three weeks, and their renewed administration resulted in full functional recovery. Beyond CMT1A, our findings can be considered as a potent therapeutic strategy for inherited peripheral neuropathies. They provide the proof of concept for a new precision medicine based on the normalization of disease gene expression by siRNA.

NDRG1-linked Charcot-Marie-Tooth disease (CMT4D) with central nervous system involvement.

Charcot-Marie-Tooth disease type 4D (CMT4D) is an autosomal recessive demyelinating polyneuropathy, associated with deafness exclusively found in Gypsies and resulting from a homozygous R148X mutation in the N-myc downstream-regulated gene 1 (NDRG1). We report the detailed phenotypic study of a family without Gypsy ancestry, who presented with severe demyelinating polyneuropathy, deafness, subcortical white matter abnormalities on brain magnetic resonance imaging studies, and the R148X mutation in NDRG1. For the first time, central nervous system white matter lesions are demonstrated in CMT4D. This report extends the clinical knowledge of CMT4D and indicates that the role of the R148X mutation in NDRG1 in the central nervous system should be further studied.

Subtle central and peripheral nervous system abnormalities in a family with centronuclear myopathy and a novel dynamin 2 gene mutation.

Mutations in dynamin 2 (DNM2), an ubiquitously-expressed large GTPase, cause autosomal dominant centronuclear myopathy (DNM2-CNM) and AD Charcot-Marie-Tooth disease type 2B (DNM2-CMT2B). We report a series of 5 patients from the same family who all presented with dominant centronuclear myopathy, mild cognitive impairment, mild axonal peripheral nerve involvement, and the novel E368Q mutation in the DNM2 gene. This study suggests that the phenotypes of dynamin 2 related centronuclear myopathy and Charcot-Marie-Tooth disease overlap and that DNM2 mutations may alter cerebral function. This report extends the clinical knowledge of DNM2-centronuclear myopathy and shows that the role of DNM2 mutations in the central nervous system should be further studied.

Phenotypic spectrum and incidence of TRPV4 mutations in patients with inherited axonal neuropathy.

OBJECTIVE: To clarify the phenotypic spectrum and incidence of TRPV4 mutations in patients with inherited axonal neuropathies. METHODS: We screened for TRPV4 mutations in 169 French unrelated patients with inherited axonal peripheral neuropathy. Ninety-five patients had dominant Charcot-Marie-Tooth type 2 (CMT2) disease, and 74 patients, including 39 patients with distal hereditary motor neuropathy, 14 with congenital spinal muscular atrophy and arthrogryposis, 13 with CMT2, and 8 with scapuloperoneal spinal muscular atrophy, presented with additional vocal cord paralysis and/or skeletal dysplasia. RESULTS: No deleterious TRPV4 mutation was identified in the 95 patients with "pure" CMT2 (0/95). In contrast, 12 of 74 patients (16%) with neuropathy and vocal cord paralysis and/or skeletal dysplasia presented pathogenic TRPV4 mutations, including 7 patients with distal hereditary motor neuropathy, 2 with scapuloperoneal spinal muscular atrophy, 2 with congenital spinal muscular atrophy and arthrogryposis, and one with CMT2. Investigation of affected relatives allowed us to study 17 patients. All patients had childhood-onset motor neuropathy and showed a variety of associated findings, including foot deformities (100% of cases), kyphoscoliosis (100%), elevated serum creatine kinase levels (100%), vocal cord paralysis (94%), scapular winging (53%), respiratory insufficiency (29%), hearing loss (24%), skeletal dysplasia (18%), and arthrogryposis (12%). Eight missense mutations were observed in these 12 families, including 2 previously unreported. Six mutations were de novo events, and 2 asymptomatic carriers were identified. CONCLUSION: With 16% of patients affected in our series, this study demonstrates that TRPV4 mutations are a major cause of inherited axonal neuropathy associated with a large spectrum of additional features.

Charcot-Marie-Tooth disease type 2A: from typical to rare phenotypic and genotypic features.

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.

SURF1 deficiency causes demyelinating Charcot-Marie-Tooth disease.

OBJECTIVE: To investigate whether mutations in the SURF1 gene are a cause of Charcot-Marie-Tooth (CMT) disease. METHODS: We describe 2 patients from a consanguineous family with demyelinating autosomal recessive CMT disease (CMT4) associated with the homozygous splice site mutation c.107-2A>G in the SURF1 gene, encoding an assembly factor of the mitochondrial respiratory chain complex IV. This observation led us to hypothesize that mutations in SURF1 might be an unrecognized cause of CMT4, and we investigated SURF1 in a total of 40 unrelated patients with CMT4 after exclusion of mutations in known CMT4 genes. The functional impact of c.107-2A>G on splicing, amount of SURF1 protein, and on complex IV activity and assembly was analyzed. RESULTS: Another patient with CMT4 was found to harbor 2 additional SURF1 mutations. All 3 patients with SURF1-associated CMT4 presented with severe childhood-onset neuropathy, motor nerve conduction velocities <25 m/s, and lactic acidosis. Two patients had brain MRI abnormalities, including putaminal and periaqueductal lesions, and developed cerebellar ataxia years after polyneuropathy. The c.107-2A>G mutation produced no normally spliced transcript, leading to SURF1 absence. However, complex IV remained partially functional in muscle and fibroblasts. CONCLUSIONS: We found SURF1 mutations in 5% of families (2/41) presenting with CMT4. SURF1 should be systematically screened in patients with childhood-onset severe demyelinating neuropathy and additional features such as lactic acidosis, brain MRI abnormalities, and cerebellar ataxia developing years after polyneuropathy.