Biallelic variants in the FIG4 gene cause Charcot-Marie-Tooth type 4J (CMT4J) and Yunis-Varon syndrome. There is increasing evidence of phenotypic overlap between CMT4J and Yunis-Varon syndrome, which presents with peripheral neuropathy and central nervous system (CNS) abnormalities, particularly parkinsonism. We aim to extend and specify the phenotype-genotype correlation of the FIG4 variants by presenting four cases of CMT4J, including two with parkinsonism. All patients carried the pathogenic FIG4 variant c.122T > C p.(Ile41Thr) in compound heterozygosity with another variant: c.793C > T p.(Arg265∗), c.498-1G > A, or c.447-2A > C. Disease onset occurred in the first or second decade of life. All presented with demyelinating sensorimotor polyneuropathy, distal muscle weakness of the upper and lower limbs, and foot deformity. In one patient, the muscle weakness was asymmetrical. Two patients developed parkinsonism. Our findings expand the phenotypic spectrum of FIG4-related disorders, reinforcing the link between CMT4J and parkinsonism. These insights are crucial for improving genetic diagnosis and advancing potential therapeutic strategies.

Charcot-Marie-Tooth disease type 4J (CMT4J) is caused by autosomal recessive variants in the Factor-Induced Gene 4 (FIG4) gene. Recent preclinical work has demonstrated the feasibility of adeno-associated virus serotype 9-FIG4 gene therapy. This study aimed to further characterize the CMT4J phenotype and evaluate feasibility of validated CMT-related outcome measures for future clinical trials. This cross-sectional study enrolled children and adults with genetically confirmed CMT4J, with 2 documented disease-causing variants in the FIG4 gene. Patients were recruited through the Inherited Neuropathy Consortium network. Disease severity was assessed using standardized CMT-specific outcome measures and exploratory biomarkers including muscle MRI fat fraction, electrophysiology, and neurofilament light chain levels. Descriptive statistics and correlation analyses were conducted to explore relationships between variables. We recruited a total of 19 patients, including 14 pediatric patients (mean age 10.9 ± 3.9 years) and 5 adults (mean age 40.0 ± 13.9 years). The most frequent symptoms were gross motor delay and distal more than proximal muscle weakness, which were observed in 14 of 19 patients. The most common non-neuromuscular symptoms were cognitive and respiratory deficits, each seen in 8 of 19 patients. We denoted asymmetric weakness in 2 patients and nonuniform slowing of conduction velocities in 6 patients. Charcot-Marie-Tooth Disease Pediatric Scale (CMTPedS), Pediatric Quality of Life Inventory, and Vineland Adaptive Behavior Scale scores were affected in most patients. We observed a significant positive correlation between neurofilament light chain levels and CMTPedS, but the study was underpowered to observe a correlation between CMTPedS and MRI fat fraction. We obtained baseline clinical and biomarker data in a broad cohort with CMT4J in pediatric and adult patients. Motor delay, muscle weakness, and respiratory and cognitive difficulties were the most common clinical manifestations of CMT4J. Many patients had nerve conduction studies with nonuniform slowing, and 2 had an asymmetric pattern of muscle weakness. We observed that the neurofilament light chain levels correlated with the CMTPedS in the pediatric population. This study showed feasibility of clinical outcomes including CMTPedS in assessment of disease severity in the pediatric patient population and provided baseline characteristics of exploratory biomarkers, neurofilament light chain levels, and muscle MRI fat fraction. The coronavirus disease 2019 pandemic affected some of the visits, resulting in a reduced number of some of the assessments.

Background/Objectives: The genetic underpinnings of Parkinson's disease (PD) and parkinsonism have drawn increasing attention in recent years. Mutations in the Factor-Induced Gene 4 (FIG4) have been implicated in various neurological disorders, including Charcot-Marie-Tooth disease type 4J (CMT4J), amyotrophic lateral sclerosis (ALS), and Yunis-Varón syndrome. This review aims to explore the association between FIG4 mutations and parkinsonism, with a specific focus on the rare missense mutation p.Ile41Thr (I41T). Methods: We identified 12 cases from 10 different families in which parkinsonism was reported in conjunction with CMT4J polyneuropathy. All cases involved the I41T mutation in a compound heterozygous state, combined with a FIG4 loss-of-function mutation. Data from clinical observations, neuroimaging studies, and genetic analyses were evaluated to understand the characteristics of parkinsonism in these patients. Results: In all 12 cases, parkinsonism developed either concurrently or following the onset of CMT4J neuropathy, but was never observed in isolation. Cases of both early- and late-onset parkinsonism were identified, reflecting similarities to genetic forms of parkinsonism with autosomal recessive inheritance. Imaging studies, including Dopamine transporter Single Photon Emission Computed Tomography (DaTscan) and brain magnetic resonance imaging (MRI), revealed abnormalities indicative of neurodegeneration, consistent with findings in other neurodegenerative disorders. Conclusions: The co-occurrence of parkinsonism with CMT4J in patients carrying the I41T mutation suggests an expanded spectrum of FIG4-related disorders, potentially implicating the same molecular mechanisms seen in other neurodegenerative disorders. Further research into FIG4-mediated pathways may offer valuable insights into potential therapeutic targets for disorders of both the central and peripheral nervous systems.

Pathogenic variants in the FIG4 gene have been described to be associated with a diverse spectrum of syndromes, such as autosomal recessive bilateral temporooccipital polymicrogyria (OMIM 612691), autosomal dominant amyotrophic lateral sclerosis-11 (ALS11; OMIM 612577), autosomal recessive Charcot-Marie-Tooth disease, type 4J (CMT4J; OMIM 611228), and autosomal recessive Yunis-Varon syndrome (YVS; OMIM 216340). Heterozygous FIG4 variants are responsible for ALS11 characterized by progressive muscular weakness, atrophy, and bulbar palsy. CMT4J is a disorder of peripheral nervous system defects mainly presenting with a highly variable onset of proximal and/or distal muscle weakness. YVS is a disorder of severe neurological involvement with central nervous system (CNS) dysfunction and extensive skeletal anomalies. We reported two Chinese siblings born with a weakness in all limbs. They experienced rapidly progressive weakness in distal limbs. At the age of 6 years, the elder brother presented with severe scoliosis and cervical kyphosis. They both had global developmental delay and a CNS involvement with cognitive deficits and swallowing problems. Genetic screening in the patients' family for inherited diseases was recommended. Novel compound heterozygous variants in the FIG4 gene (c.2148delTinsAA and c.317A > G) were found by whole-exome sequencing in the patients. These variants were confirmed by Sanger sequencing in family members. Herein, we reported two Chinese male patients with CMT4J who presented with abnormal CNS features. CMT4J with CNS involvement has been very rarely reported. We hoped this study could expand the phenotypic and genetic spectrum of FIG4-related diseases. And we helped physicians to understand the genotype-phenotype correlation.

Charcot-Marie-Tooth (CMT) disease is mainly a disease of peripheral nervous system and patients typically present with features of demyelinating neuropathy or axonal neuropathy or both. Rarely patients present with features of central nervous system involvement. Parkinsonism, aphemia and familial epilepsy syndrome have previously come up as case reports in association with CMT type 4 J.We hereby describe a family with 3 siblings affected with CMT4J with homozygous FIG4 mutation who presented with global developmental delay, epilepsy and spastic quadriparesis.