Biallelic variants in sorbitol dehydrogenase (SORD) have been reported to be a major cause of autosomal recessive distal hereditary motor neuropathy (dHMN). In this study, the clinical and pathological features of 10 patients with SORD gene-related dHMN are reported. Homozygous c.757delG variant was detected in 6 patients while c.757delG, c.786 + 1G>A, c.218C>T, and a novel c.104T>A compound heterozygous variants were observed in the others. Serum sorbitol, xylitol, and D-arabinitol were measured by gas chromatography-mass spectrometry; increased sorbitol and xylitol, and decreased D-arabinitol were identified. Sural nerve biopsies showed mild loss of large, myelinated fibers, and a few thin myelinated fibers. Skeletal muscle biopsies exhibited a neurogenic pattern with vacuoles, tubular aggregates, and abnormal mitochondria. Proteomic analyses of muscle tissue were performed to explore potential mechanisms. Complex I deficiency was dominant in the proteomic analysis and the malic acid/oxaloacetic acid ratio was significantly higher in the patients than in controls. In summary, SORD gene-related dHMN is a systemic disorder of carbohydrate metabolism with subclinical myopathologic changes, including tubular aggregates and vacuoles. Mitochondrial complex I deficiency, may be a key mechanism in SORD gene-related dHMN. MFN2 hereditary motor and sensory neuropathy (MFN2-HMSN) is a classic axonal peripheral sensorimotor neuropathy, inherited in either an autosomal dominant (AD) manner (~90%) or an autosomal recessive (AR) manner (~10%). MFN2-HMSN is characterized by more severe involvement of the lower extremities than the upper extremities, distal upper-extremity involvement as the neuropathy progresses, more prominent motor deficits than sensory deficits, and normal (>42 m/s) or only slightly decreased nerve conduction velocities (NCVs). Postural tremor is common. Median onset is age 12 years in the AD form and age eight years in the AR form. The prevalence of optic atrophy is approximately 7% in the AD form and approximately 20% in the AR form. Molecular genetic testing establishes the diagnosis of MFN2-HMSN in 90% of probands with suggestive findings by identifying a heterozygous MFN2 pathogenic variant and in 10% of probands with suggestive findings by identifying biallelic MFN2 pathogenic variants. Treatment of manifestations: Neuropathy is often managed by a multidisciplinary team that includes a neurologist, a physiatrist, an orthopedic surgeon, and physical and occupational therapists. Symptomatic treatment relies on special shoes and/or ankle/foot orthoses to correct foot drop and aid walking; surgery as needed for severe pes cavus; forearm crutches, canes, wheelchairs as needed for mobility; exercise as tolerated; acetaminophen or nonsteroidal anti-inflammatory agents for musculoskeletal pain; treatment of neuropathic pain with tricyclic antidepressants or drugs such as carbamazepine or gabapentin. Optic atrophy is managed with low vision aids as per a low vision clinic, consultation with community vision services, and career/employment counseling. Surveillance: Routine evaluation by: a neurologist to assess disease progression; physical therapy to assess gross motor skills including gait and strength; occupational therapy to assess fine motor skills and coping strategies; and ophthalmologist and low vision clinic to assess visual acuity and need for modification of low vision aids, respectively. Agents/circumstances to avoid: Obesity (which makes ambulation more difficult); medications (e.g., vincristine, isoniazid, nitrofurantoin) known to cause nerve damage; alcohol and malnutrition (which can cause or exacerbate neuropathy). Approximately 90% of MFN2-HMSN is inherited an autosomal dominant (AD) manner, and approximately 10% is inherited in an autosomal recessive (AR) manner. Semi-dominant inheritance (i.e., an MFN2 pathogenic variant is associated with mild disease in the heterozygous state and more severe disease in the homozygous or compound heterozygous state) has been reported in two families. AD MFN2-HMSN. Most affected individuals have an affected parent; the proportion of individuals with a de novo MFN2 pathogenic variant is unknown. Each child of an affected individual has a 50% chance of inheriting the MFN2 pathogenic variant. AR MFN2-HMSN. At conception, each sib of an individual with autosomal recessive MFN2-HMSN has a 25% chance of being affected, a 50% chance of being an asymptomatic heterozygote (i.e., carrier), and a 25% chance of being unaffected and not a carrier. Once the MFN2 pathogenic variant(s) have been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing for MFN2-HMSN are possible.

Objective: Vaccinia-related kinase 1 (VRK1)-related disease is an extremely rare autosomal recessive disorder primarily affecting the peripheral and/or central nervous system. In this report, we describe the genetic and clinical features of two siblings from a Turkish family presenting with an amyotrophic lateral sclerosis (ALS) phenotype due to a novel homozygous VRK1 mutation, and discuss the broad phenotypic spectrum associated with pathogenic variants in this gene. Methods: We analyzed the demographic data, clinical histories, neurological examinations, laboratory findings, and genetic results of 53 patients, including our cases, derived from 27 different reports. Results: Whole-exome sequencing identified a novel homozygous missense mutation, c.700A > G (p.Asn234Asp), in the VRK1 gene in two affected siblings. The characteristic features of the ALS phenotype included a recessive inheritance pattern, motor deficits with onset in the lower limbs, pyramidal tract signs, and a muscle magnetic resonance imaging (MRI) pattern demonstrating preferential involvement of the posterior compartments of the leg and thigh. The most common phenotypes associated with VRK1 mutations were ALS (18/53, 34%) and distal hereditary motor neuropathy (dHMN) (14/53, 26.4%), followed by pontocerebellar hypoplasia type 1 (7/53, 13.2%), hereditary motor and sensory neuropathy (5/53, 9.4%), autosomal recessive primary microcephaly with brain malformations (4/53, 7.5%), and spastic paraplegia (2/53, 3.8%). The ALS phenotype exhibited a significantly earlier mean age of onset compared to the dHMN phenotype (p = 0.015; 15.3 ± 11.5 and 27 ± 15.5 years, respectively). Conclusion: Our findings highlight the importance of investigating VRK1 mutations in patients with young-onset familial ALS. Furthermore, this report provides a systematic classification of the phenotype definitions associated with VRK1 mutations. NARS1-related neurologic disorders encompass NARS1-related neurodevelopmental disorder (NARS1-NDD), a neonatal- or childhood-onset phenotype with central nervous system and peripheral nervous system involvement, and NARS1-related hereditary neuropathy, an adolescent- or early adult-onset hereditary neuropathy. NARS1-NDD manifests with global developmental delay, intellectual disability, microcephaly, ataxia, seizures, and, rarely, neurobehavioral/psychiatric manifestations. Change in muscle tone can manifest either as spasticity or as hypotonia. Peripheral neuropathy with atrophy predominantly of the distal lower limbs can be associated. NARS1-related hereditary neuropathy manifests with mostly motor and sensory impairment involving weakness of predominantly the distal lower limbs and foot deformities, without prominent muscle atrophy. A few individuals have been described with isolated hereditary motor neuropathy associated with foot deformities, ankle contractures, kyphosis, hyperlaxity, and brisk reflexes. To date, 54 individuals from 30 families with NARS1 pathogenic variant(s) have been reported. The diagnosis of a NARS1-related neurologic disorder is established in a proband with suggestive findings and either biallelic or heterozygous NARS1 pathogenic variants in those with NARS1-NDD or a NARS1 heterozygous pathogenic variant in those with NARS1-related hereditary neuropathy identified by molecular genetic testing. Treatment of manifestations: Individuals with NARS1-NDD: multidisciplinary care by specialists in relevant fields including developmental pediatrics, speech and language therapy, neurology to manage seizures, physical therapy, orthopedics to manage scoliosis/kyphoscoliosis, nutrition/feeding, psychology to manage behavioral abnormalities, and medical genetics / genetic counseling. Individuals with NARS1-related hereditary neuropathy: follow standard practice for peripheral neuropathy. Surveillance: Individuals with NARS1-NDD: monitoring at each visit or per the treating specialist. NARS1-NDD can be inherited in an autosomal recessive or autosomal dominant manner. NARS1-related hereditary neuropathy is inherited in an autosomal dominant manner. Autosomal recessive inheritance: If both parents are known to be heterozygous for a NARS1 pathogenic variant, each sib of an individual with autosomal recessive NARS1-NDD has at conception a 25% chance of being affected, a 50% chance of being heterozygous, and a 25% chance of inheriting neither of the familial pathogenic variants. Heterozygous sibs of a proband with autosomal recessive NARS1-NDD are asymptomatic and are not at risk of developing a NARS1-related neurologic disorder. Carrier testing for at-risk relatives requires prior identification of the NARS1 pathogenic variants in the family. Autosomal dominant inheritance: The proportion of individuals with an autosomal dominant NARS1-related neurologic disorder who have the disorder as the result of a de novo pathogenic variant varies by phenotype. All probands reported to date with autosomal dominant NARS1-NDD (whose parents have undergone molecular genetic testing) have the disorder as the result of a de novo NARS1 pathogenic variant. Some individuals with NARS1-related hereditary neuropathy have the disorder as the result of a de novo NARS1 pathogenic variant. Each child of an individual with an autosomal dominant NARS1-related neurologic disorder has a 50% chance of inheriting the pathogenic variant. Once the NARS1 pathogenic variant(s) have been identified in an affected family member, prenatal and preimplantation genetic testing are possible.

A newly identified subtype of hereditary axonal motor neuropathy, characterized by early proximal limb involvement, has been discovered in a cohort of 34 individuals with biallelic variants in von Willebrand factor A domain-containing 1 (VWA1). This study further delineates the disease characteristics in a cohort of 20 individuals diagnosed through genome or exome sequencing, incorporating neurophysiological, laboratory and imaging data, along with data from previously reported cases across three different studies. Newly reported clinical features include hypermobility/hyperlaxity, axial weakness, dysmorphic signs, asymmetric presentation, dystonic features and, notably, upper motor neuron signs. Foot drop, foot deformities and distal leg weakness followed by early proximal leg weakness are confirmed to be initial manifestations. Additionally, this study identified 11 novel VWA1 variants, reaffirming the 10 bp insertion-induced p.Gly25ArgfsTer74 as the most prevalent disease-causing allele, with a carrier frequency of ∼1 in 441 in the UK and Western European population. Importantly, VWA1-related pathology may mimic various neuromuscular conditions, advocating for its inclusion in diverse gene panels spanning hereditary neuropathies to muscular dystrophies. The study highlights the potential of lower quality control filters in exome analysis to enhance diagnostic yield of VWA1 disease that may account for up to 1% of unexplained hereditary neuropathies.

Heterozygous RTN2 variants have been previously identified in a limited cohort of families affected by autosomal dominant spastic paraplegia (SPG12-OMIM:604805) with a variable age of onset. Nevertheless, the definitive validity of SPG12 remains to be confidently confirmed due to the scarcity of supporting evidence. In this study, we identified and validated seven novel or ultra-rare homozygous loss-of-function RTN2 variants in 14 individuals from seven consanguineous families with distal hereditary motor neuropathy (dHMN) using exome, genome and Sanger sequencing coupled with deep-phenotyping. All affected individuals (seven males and seven females, aged 9-50 years) exhibited weakness in the distal upper and lower limbs, lower limb spasticity and hyperreflexia, with onset in the first decade of life. Nerve conduction studies revealed axonal motor neuropathy with neurogenic changes in the electromyography. Despite a slowly progressive disease course, all patients remained ambulatory over a mean disease duration of 19.71 ± 13.70 years. Characterization of Caenorhabditis elegans RTN2 homologous loss-of-function variants demonstrated morphological and behavioural differences compared with the parental strain. Treatment of the mutant with an endoplasmic/sarcoplasmic reticulum Ca2+ reuptake inhibitor (2,5-di-tert-butylhydroquinone) rescued key phenotypic differences, suggesting a potential therapeutic benefit for RTN2-disorder. Despite RTN2 being an endoplasmic reticulum (ER)-resident membrane shaping protein, our analysis of patient fibroblast cells did not find significant alterations in ER structure or the response to ER stress. Our findings delineate a distinct form of autosomal recessive dHMN with pyramidal features associated with RTN2 deficiency. This phenotype shares similarities with SIGMAR1-related dHMN and Silver-like syndromes, providing valuable insights into the clinical spectrum and potential therapeutic strategies for RTN2-related dHMN.

Biallelic mutations in the coenzyme Q7 (COQ7) encoding gene were recently identified as a genetic cause of distal hereditary motor neuropathy. Here, we explored the clinical, electrophysiological, pathological, and genetic characteristics of a Chinese patient with spastic paraplegia associated with recessive variants in COQ7. This patient carried a novel c.322C>A (p.Pro108Thr) homozygous variant. Sural biopsy revealed mild mixed axonal and demyelinating degeneration. Immunoblotting showed a significant decrease in the COQ7 protein level in the patient's fibroblasts. This study confirmed that COQ7 variant as a genetic cause of HSP, and further extended spastic paraplegia to the phenotypic spectrum of COQ7-related disorders.