Homozygous SOD1 Variation L144S Produces a Severe Form of Amyotrophic Lateral Sclerosis in an Iranian Family

A homozygous p.Val120Leu (c.358G > C) SOD1 mutation led to slowly progressive amyotrophic lateral sclerosis in a Brazilian family

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease usually associated with severe weakness and death within 2-5 years. SOD1 mutations cause hereditary ALS in autosomal dominant and rarely in recessive pattern. We describe a new phenotype of slowly progressive fALS due to homozygous SOD1 mutations (c.358G > C, p.Val120Leu) in a Brazilian family. We reviewed the medical chart and interviewed the index patient and other relatives. A 41-year-old man developed weakness in his legs, leading to frequent falls, followed over the next few months with progressive arm fasciculations and muscle atrophy. The SOD1 enzymatic activity in erythrocytes was slightly decreased. A genetic test panel disclosed homozygous SOD1 mutations (c.358G > C, p.Val120Leu). His asymptomatic parents also carried one mutant allele and 2 brothers and a sister had died with ALS. We reported a new family with homozygous SOD1 mutation and slowly progressive ALS course. Further studies are necessary to confirm whether this mutation can also lead to disease in heterozygosis with incomplete penetrance.

Discovery of a novel homozygous SOD1 truncating variant bolsters infantile SOD1 deficiency syndrome

OBJECTIVE

Superoxide dismutase 1 (SOD1) is an important antioxidant enzyme whose main function is to neutralise superoxide free radicals in the cytoplasm. Heterozygous variants in SOD1 are responsible for a substantial percentage of familial amyotrophic lateral sclerosis (ALS) cases. Recently, several reports have shown that biallelic loss of SOD1 function results in a novel phenotype called infantile SOD1 deficiency syndrome, which is consistent with a recessive pattern of inheritance and can be distinguished from typical (adult-onset) ALS.

METHODS

We documented detailed family histories and clinical data, followed by whole-exome sequencing and family co-segregation analysis through Sanger sequencing. To facilitate comparisons, relevant data from fifteen previously reported patients with SOD1-related neurodevelopmental disorders were included.

RESULTS

This study presents a new Turkish family with two affected children exhibiting severe delayed motor development, infancy-onset loss of motor skills, axial hypotonia, tetraspasticity, and impaired cognitive functions. Genetic analysis revealed a novel homozygous frameshift variant in SOD1 (c.248dupG [p.Asp84Argfs*8]), with computational biochemical studies shedding light on the mechanistic aspects of SOD1 dysfunction.

CONCLUSIONS

Our findings contribute an affirmative report of a fourth biallelic variant resulting in a severe clinical phenotype, reminiscent of those induced by previously identified homozygous loss-of-function SOD1 variants. This research not only advances our understanding of the pathogenesis of this debilitating neurological syndrome but also aligns with ongoing intensive efforts to comprehend and address SOD1-linked ALS.

Unraveling the Genetic Landscape of Neurological Disorders: Insights into Pathogenesis, Techniques for Variant Identification, and Therapeutic Approaches

Genetic abnormalities play a crucial role in the development of neurodegenerative disorders (NDDs). Genetic exploration has indeed contributed to unraveling the molecular complexities responsible for the etiology and progression of various NDDs. The intricate nature of rare and common variants in NDDs contributes to a limited understanding of the genetic risk factors associated with them. Advancements in next-generation sequencing have made whole-genome sequencing and whole-exome sequencing possible, allowing the identification of rare variants with substantial effects, and improving the understanding of both Mendelian and complex neurological conditions. The resurgence of gene therapy holds the promise of targeting the etiology of diseases and ensuring a sustained correction. This approach is particularly enticing for neurodegenerative diseases, where traditional pharmacological methods have fallen short. In the context of our exploration of the genetic epidemiology of the three most prevalent NDDs-amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease, our primary goal is to underscore the progress made in the development of next-generation sequencing. This progress aims to enhance our understanding of the disease mechanisms and explore gene-based therapies for NDDs. Throughout this review, we focus on genetic variations, methodologies for their identification, the associated pathophysiology, and the promising potential of gene therapy. Ultimately, our objective is to provide a comprehensive and forward-looking perspective on the emerging research arena of NDDs.

The landscape of cognitive impairment in superoxide dismutase 1-amyotrophic lateral sclerosis

Although mutations in the superoxide dismutase 1 gene account for only a minority of total amyotrophic lateral sclerosis cases, the discovery of this gene has been crucial for amyotrophic lateral sclerosis research. Since the identification of superoxide dismutase 1 in 1993, the field of amyotrophic lateral sclerosis genetics has considerably widened, improving our understanding of the diverse pathogenic basis of amyotrophic lateral sclerosis. In this review, we focus on cognitive impairment in superoxide dismutase 1-amyotrophic lateral sclerosis patients. Literature has mostly reported that cognition remains intact in superoxide dismutase 1-amyotrophic lateral sclerosis patients, but recent reports highlight frontal lobe function frailty in patients carrying different superoxide dismutase 1-amyotrophic lateral sclerosis mutations. We thoroughly reviewed all the various mutations reported in the literature to contribute to a comprehensive database of superoxide dismutase 1-amyotrophic lateral sclerosis genotype-phenotype correlation. Such a resource could ultimately improve our mechanistic understanding of amyotrophic lateral sclerosis, enabling a more robust assessment of how the amyotrophic lateral sclerosis phenotype responds to different variants across genes, which is important for the therapeutic strategy targeting genetic mutations. Cognition in superoxide dismutase 1-amyotrophic lateral sclerosis deserves further longitudinal research since this peculiar frailty in patients with similar mutations can be conditioned by external factors, including environment and other unidentified agents including modifier genes.

Clinical and molecular features of patients with amyotrophic lateral sclerosis and SOD1 mutations: a monocentric study

Introduction

SOD1 was the first gene associated with both familial and sporadic forms of amyotrophic lateral sclerosis (ALS) and is the second most mutated gene in Caucasian ALS patients. Given their high clinical and molecular heterogeneity, a detailed characterization of SOD1-ALS patients could improve knowledge about the natural history of this disease. Here, the authors aimed to provide a clinical and molecular description of a monocentric cohort of SOD1-ALS patients.

Methods

Amyotrophic lateral sclerosis (ALS) patients referring to the neurology unit of our center between 2008 and 2021 were clinically assessed and underwent molecular testing for SOD1. Segregation studies in available family members and in silico analysis were performed to sustain the pathogenicity of the identified SOD1 variants.

Results

Among the 576 patients in our cohort, we identified 19 individuals harboring a mutation in SOD1 (3.3%), including 15 (78.9%) with a familial and four (21.1%) with a sporadic form. The spinal onset of the disease was observed in all patients, and survival was extremely variable, ranging from 8 months to over 30 years. Twelve different SOD1 missense variants were identified in our cohort, including one novel mutation (p.Pro67Leu).

Discussion

In the present series, we provided the first description of an Italian monocentric cohort of SOD1-ALS patients, and we expanded the repertoire of SOD1 mutations. Our cohort presents several remarkable features, including variable expressivity in the same family, atypical presentation (ataxia, cognitive impairment, and other extra-motor symptoms), and different modes of inheritance of a given mutation in the same family. Given the recent authorization of SOD1-directed antisense oligonucleotide for use in SOD1-ALS patients, we recommend prompt screening for SOD1 mutations in novel ALS patients with familiar or sporadic presentations.

A novel homozygous p.Ser69Pro SOD1 mutation causes severe young-onset ALS with decreased enzyme activity

BACKGROUND

The dose-effect of various SOD1 mutations on SOD1 enzymatic activity offers valuable insights into ALS pathogenesis with possible therapeutic implications. Homozygous SOD1 mutations, yet scarce, are of special interest. We report a novel homozygous SOD1 mutation with decreased enzymatic activity and severe early onset ALS phenotype.

METHODS

Whole exome sequencing and targeted screening of commonly implicated genes were conducted. Repeat-primed PCR and fragment length analysis were used for C9orf72. Bi-directional Sanger sequencing was used for SOD1 and other genes. SOD1 activity was measured by direct spectrophotometry. Serum neurofilament light chain level was measured by the ELLA immunoassay system.

RESULTS

The homozygous patient for a novel SOD1 variant p.Ser69Pro showed poor SOD1 enzymatic activity (16% of controls) and an early onset ALS phenotype predominantly affecting lower motor neurons with rapid involvement of the trunk, upper limbs and bulbar muscles. The asymptomatic heterozygous relatives had at least 68% of normal enzyme activity. Level of serum neurofilament light chain was much higher (148 pg/ml) in the patient than the relatives who had normal levels (6-10 pg/ml).

CONCLUSION

This novel mutation adds knowledge to the ALS genotype-phenotype spectrum and supports the strong dose-effect of SOD1 mutations associated with severely decreased enzymatic activity.

Case report: Flail leg syndrome in familial amyotrophic lateral sclerosis with L144S SOD1 mutation

We observed a Polish family with familial amyotrophic lateral sclerosis with heterozygous L144S SOD1 mutation, which manifested clinically as flail leg syndrome. Flail leg syndrome is a rare phenotype of amyotrophic lateral sclerosis, with slow progression, long survival, and predominance of lower motor neuron signs at onset, as a triad of distal paresis, muscle atrophy, and hyporeflexia/areflexia, confined to the lower limbs for an extended period of time. Although familial amyotrophic lateral sclerosis is usually associated with a worse prognosis than the sporadic form of the disease, the clinical course of the disease in patients with L144S SOD1 mutation is benign, with slow progression and long survival. This unique case report provides an in-depth clinical analysis of all of the symptomatic members of a family, who were diagnosed with amyotrophic lateral sclerosis in our clinic, including three siblings (two brothers and a deceased sister) with flail leg syndrome and their fraternal aunt, who has been previously misdiagnosed with cervical myelopathy and is living with symptoms of the disease for 15 years. Sanger sequencing of the SOD1 gene was performed in all of the living patients, revealing an L144S (c.434T>C, p.Leu145Ser) heterozygous mutation. The aim of this case report is to increase the physician's awareness of the atypical phenotypes of amyotrophic lateral sclerosis and hopefully, to encourage further research on the factors responsible for delayed disease progression in patients with L144S SOD1 mutation.