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Dominant missense mutations of the calcium-permeable cation channel TRPV4 cause Charcot-Marie-Tooth disease (CMT) type 2C and two forms of distal spinal muscular atrophy. These conditions are collectively referred to as TRPV4-related neuromuscular disease and share features of motor greater than sensory dysfunction and frequent vocal fold weakness. Pathogenic variants lead to gain of ion channel function that can be rescued by TRPV4 antagonists in cellular and animal models. As small molecule TRPV4 antagonists have proven safe in trials for other disease indications, channel inhibition is a promising therapeutic strategy for TRPV4 patients. However, the current knowledge of the clinical features and natural history of TRPV4-related neuromuscular disease is insufficient to enable rational clinical trial design. To address these issues, we developed a TRPV4 patient database and administered a TRPV4-specific patient questionnaire. Here, we report demographic and clinical information, including CMT Examination Scores (CMTES), from 68 patients with known pathogenic TRPV4 variants, 40 of whom also completed the TRPV4 patient questionnaire. TRPV4 patients showed a bimodal age of onset, with the largest peak occurring in the first 2 years of life. Compared to CMT type 1A (CMT1A) patients, TRPV4 patients showed distinct symptoms and signs, manifesting more ambulatory difficulties and more frequent involvement of proximal arm and leg muscles. Although patients reported fewer sensory symptoms, sensory dysfunction was often detected clinically. Many patients were affected by vocal fold weakness (55%) and shortness of breath (55%), and 11% required ventilatory support. Skeletal abnormalities were common, including scoliosis (64%), arthrogryposis (33%) and foot deformities. Strikingly, patients with infantile onset of disease showed less sensory involvement and less progression of symptoms. These results highlight distinctive clinical features in TRPV4 patients, including motor-predominant disease, proximal arm and leg weakness, severe ambulatory difficulties, vocal fold weakness, respiratory dysfunction and skeletal involvement. In addition, patients with infantile onset of disease appeared to have a distinct phenotype with less apparent disease progression based on CMTES. These collective observations indicate that clinical trial design for TRPV4-related neuromuscular disease should include outcome measures that reliably capture non-length dependent motor dysfunction, vocal fold weakness and respiratory disease. [ABSTRACT FROM AUTHOR]

Background and Aims: The Charcot–Marie–Tooth Disease Health Index (CMT‐HI) is a disease‐specific, patient‐reported disease burden measure. As part of an international clinical trial readiness study, individuals with CMT1A (ages 18–75 years) underwent clinical outcome assessments (COAs), including the CMT‐HI, to capture their longitudinal perspective on the disease burden. Methods: Two hundred and fifteen participants underwent serial COAs including the CMT‐HI, CMT Functional Outcome Measure (CMT‐FOM), CMT Neuropathy Score (CMTNSv2R), and CMT Exam Score (CMTES/CMTES‐R). Correlations between the total and subscale scores for the CMT‐HI and other COAs were determined. Changes in the CMT‐HI scores over 12 months were assessed using paired t‐tests. The minimum clinically important difference (MCID) for the CMT‐HI and its subscales were calculated by anchoring to a participant global impression of change scale. Results: At baseline, CMT1A participants were 44.5 ± 15 years old (range: 18–75) and 58% were women. The mean CMT‐HI was 25.7 ± 18.8 (range: 0–91.9; 100 reflecting maximal disease burden). The CMT‐HI correlated with the CMT‐FOM (r =.54, p <.0001), CMTNSv2R (r =.48, p <.0001), and CMTES/CMTES‐R (r =.52/r =.54, p <.0001). Disease burden was greater in women than in men (CMT‐HI 29.1 ± 19.1 vs. 21.2 ± 17.3, p =.001). Over 12 months, there was a nonsignificant mean increase in CMT‐HI of 0.40 ± 10.0 (n = 189, p =.89). The MCID for the CMT‐HI total score was 3.8 points (95% CI: 1.7–5.9). Discussion: Patient‐reported disease burden in CMT1A as measured by the CMT‐HI is associated with measures of neurologic impairment and physical functioning. Women reported a higher disease burden than men. These data will inform the design of clinical trials in CMT1A. [ABSTRACT FROM AUTHOR]

Background: Biallelic intronic AAGGG repeat expansions in the replication factor complex subunit 1 (RFC1) gene were identified as the leading cause of cerebellar ataxia, neuropathy, vestibular areflexia syndrome. Patients exhibit significant clinical heterogeneity and variable disease course, but no potential biomarker has been identified to date. Objectives: In this multicenter cross‐sectional study, we aimed to evaluate neurofilament light (NfL) chain serum levels in a cohort of RFC1 disease patients and to correlate NfL serum concentrations with clinical phenotype and disease severity. Methods: Sixty‐one patients with genetically confirmed RFC1 disease and 48 healthy controls (HCs) were enrolled from six neurological centers. Serum NfL concentration was measured using the single molecule array assay technique. Results: Serum NfL concentration was significantly higher in patients with RFC1 disease compared to age‐ and‐sex‐matched HCs (P < 0.0001). NfL level showed a moderate correlation with age in both HCs (r = 0.4353, P = 0.0020) and patients (r = 0.4092, P = 0.0011). Mean NfL concentration appeared to be significantly higher in patients with cerebellar involvement compared to patients without cerebellar dysfunction (27.88 vs. 21.84 pg/mL, P = 0.0081). The association between cerebellar involvement and NfL remained significant after controlling for age and sex (β = 0.260, P = 0.034). Conclusions: Serum NfL levels are significantly higher in patients with RFC1 disease compared to HCs and correlate with cerebellar involvement. Longitudinal studies are warranted to assess its change over time. [ABSTRACT FROM AUTHOR]

Charcot-Marie-Tooth disease (CMT) due to GJB1 variants (CMTX1) is the second most common form of CMT. It is an X-linked disorder characterized by progressive sensory and motor neuropathy with males affected more severely than females. Many reported GJB1 variants remain classified as variants of uncertain significance (VUS). In this large, international, multicentre study we prospectively collected demographic, clinical and genetic data on patients with CMT associated with GJB1 variants. Pathogenicity for each variant was defined using adapted American College of Medical Genetics criteria. Baseline and longitudinal analyses were conducted to study genotype-phenotype correlations, to calculate longitudinal change using the CMT Examination Score (CMTES), to compare males versus females, and pathogenic/likely pathogenic (P/LP) variants versus VUS. We present 387 patients from 295 families harbouring 154 variants in GJB1. Of these, 319 patients (82.4%) were deemed to have P/LP variants, 65 had VUS (16.8%) and three benign variants (0.8%; excluded from analysis); an increased proportion of patients with P/LP variants compared with using ClinVar's classification (74.6%). Male patients (166/319, 52.0%, P/LP only) were more severely affected at baseline. Baseline measures in patients with P/LP variants and VUS showed no significant differences, and regression analysis suggested the disease groups were near identical at baseline. Genotype-phenotype analysis suggested c.-17G>A produces the most severe phenotype of the five most common variants, and missense variants in the intracellular domain are less severe than other domains. Progression of disease was seen with increasing CMTES over time up to 8 years follow-up. Standard response mean (SRM), a measure of outcome responsiveness, peaked at 3 years with moderate responsiveness [change in CMTES (ΔCMTES) = 1.3 ± 2.6, P = 0.00016, SRM = 0.50]. Males and females progressed similarly up to 8 years, but baseline regression analysis suggested that over a longer period, females progress more slowly. Progression was most pronounced for mild phenotypes (CMTES = 0–7; 3-year ΔCMTES = 2.3 ± 2.5, P = 0.001, SRM = 0.90). Enhanced variant interpretation has yielded an increased proportion of GJB1 variants classified as P/LP and will aid future variant interpretation in this gene. Baseline and longitudinal analysis of this large cohort of CMTX1 patients describes the natural history of the disease including the rate of progression; CMTES showed moderate responsiveness for the whole group at 3 years and higher responsiveness for the mild group at 3, 4 and 5 years. These results have implications for patient selection for upcoming clinical trials. [ABSTRACT FROM AUTHOR]

Background and purpose: Data are reported from the Italian CMT Registry. Methods: The Italian CMT Registry is a dual registry where the patient registers and chooses a reference center where the attending clinician collects a minimal dataset of information and administers the Charcot–Marie–Tooth (CMT) Examination/Neuropathy Score. Entered data are encrypted. Results: Overall, 1012 patients had registered (535 females) and 711 had received a genetic diagnosis. Demyelinating CMT (65.3%) was more common than axonal CMT2 (24.6%) and intermediate CMT (9.0%). The PMP22 duplication was the most frequent mutation (45.2%), followed by variants in GJB1 and MPZ (both ~10%) and MFN2 (3.3%) genes. A relatively high mutation rate in some "rare" genes (HSPB1 1.6%, NEFL 1.5%, SH3TC2 1.5%) and the presence of multiple mutation clusters across Italy was observed. CMT4A was the most disabling type, followed by CMT4C and CMT1E. Disease progression rate differed depending on the CMT subtype. Foot deformities and walking difficulties were the main features. Shoe inserts and orthotic aids were used by almost one‐half of all patients. Scoliosis was present in 20% of patients, especially in CMT4C. Recessive forms had more frequently walking delay, walking support need and wheelchair use. Hip dysplasia occurred in early‐onset CMT. Conclusions: The Italian CMT Registry has proven to be a powerful data source to collect information about epidemiology and genetic distribution, clinical features and disease progression of CMT in Italy and is a useful tool for recruiting patients in forthcoming clinical trials. [ABSTRACT FROM AUTHOR]

Objective: The paucity of longitudinal natural history studies in MPZ neuropathy remains a barrier to clinical trials. We have completed a longitudinal natural history study in patients with MPZ neuropathies across 13 sites of the Inherited Neuropathies Consortium. Methods: Change in Charcot–Marie–Tooth Examination Score (CMTES) and Rasch modified CMTES (CMTES‐R) were evaluated using longitudinal regression over a 5‐year period in subjects with MPZ neuropathy. Data from 139 patients with MPZ neuropathy were examined. Results: The average baseline CMTES and CMTES‐R were 10.84 (standard deviation [SD] = 6.0, range = 0–28) and 14.60 (SD = 7.56, range = 0–32), respectively. A mixed regression model showed significant change in CMTES at years 2–5 (mean change from baseline of 0.87 points at 2 years, p = 0.008). Subgroup analysis revealed greater change in CMTES at 2 years in subjects with axonal as compared to demyelinating neuropathy (mean change of 1.30 points [p = 0.016] vs 0.06 points [p = 0.889]). Patients with a moderate baseline neuropathy severity also showed more notable change, by estimate, than those with mild or severe neuropathy (mean 2‐year change of 1.14 for baseline CMTES 8–14 [p = 0.025] vs −0.03 for baseline CMTES 0–7 [p = 0.958] and 0.25 for baseline CMTES ≥ 15 [p = 0.6897]). The progression in patients harboring specific MPZ mutations was highly variable. Interpretation: CMTES is sensitive to change over time in adult patients with axonal but not demyelinating forms of MPZ neuropathy. Change in CMTES was greatest in patients with moderate baseline disease severity. These findings will inform future clinical trials of MPZ neuropathies. ANN NEUROL 2023;93:563–576 [ABSTRACT FROM AUTHOR]

Background and purpose: Charcot–Marie–Tooth disease (CMT) is a heterogeneous group of disorders caused by mutations in at least 100 genes. However, approximately 60% of cases with axonal neuropathies (CMT2) still remain without a genetic diagnosis. We aimed at identifying novel disease genes responsible for CMT2. Methods: We performed whole exome sequencing and targeted next generation sequencing panel analyses on a cohort of CMT2 families with evidence for autosomal recessive inheritance. We also performed functional studies to explore the pathogenetic role of selected variants. Results: We identified rare, recessive variants in the MYO9B (myosin IX) gene in two families with CMT2. MYO9B has not yet been associated with a human disease. MYO9B is an unconventional single‐headed processive myosin motor protein with signaling properties, and, consistent with this, our results indicate that a variant occurring in the MYO9B motor domain impairs protein expression level and motor activity. Interestingly, a Myo9b‐null mouse has degenerating axons in sciatic nerves and optic nerves, indicating that MYO9B plays an essential role in both peripheral nervous system and central nervous system axons, respectively. The degeneration observed in the optic nerve prompted us to screen for MYO9B mutations in a cohort of patients with optic atrophy (OA). Consistent with this, we found compound heterozygous variants in one case with isolated OA. Conclusions: Novel or very rare variants in MYO9B are associated with CMT2 and isolated OA. [ABSTRACT FROM AUTHOR]