A novel SOD1 mutation in an Austrian family with amyotrophic lateral sclerosis

Sixteen novel mutations in the Cu/Zn superoxide dismutase gene in amyotrophic lateral sclerosis: a decade of discoveries, defects and disputes

OBJECTIVE

Since the discovery of mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) ten years ago, testing for SOD1 gene mutations has become a part of the investigation of patients with suspected motor neuron disease. We searched for novel SOD1 mutations and for clinical characteristics of patients with these mutations.

METHODS

Analysis was made of patient files at the Neurogenetic DNA Diagnostic Laboratory at Massachusetts General Hospital. We also scrutinized available medical records and examined patients with the different SOD1 mutations.

RESULTS

One hundred and forty eight (148) of 2045 amyotrophic lateral sclerosis (ALS) patients carried a disease-associated mutation in the SOD1 gene. The most prevalent was the A4V missense mutation, found in 41% of those patients. Sixteen novel exonic mutations (L8V, F20C, Q22L, H48R, T54R, S591, V87A, T88deltaTAD, A89T, V97M, S105deltaSL, V118L, D124G, G141X, G147R, 11515) were found, bringing the total number of SOD1 gene mutations in ALS to 105.

CONCLUSIONS

Mutations in the SOD1 gene are found both in sporadic and familial ALS cases without any definite predilection for any part of the gene. A common structural denominator for the 16 novel mutations or previously reported mutations is not obvious. Similarly, the nature of the putative acquired toxic function of mutant SOD1 remains unresolved. We conclude that patients with SOD1 mutations may infrequently show symptoms and signs unrelated to the motor systems, sometimes obscuring the diagnosis of ALS.

Hoarseness due to bilateral vocal cord paralysis as an initial manifestation of familial amyotrophic lateral sclerosis

Bulbar palsy is unusual as an initial manifestation of amyotrophic lateral sclerosis (ALS), although common in the advanced stages. In terms of bulbar palsy as a presenting symptom, dysarthria and dysphagia are of common features. Hoarseness, however, is an initial symptom of ALS in only a small number of patients. We report a 43-year-old female with hoarseness due to bilateral vocal cord paralysis as the first manifestation of ALS. Gene analysis revealed a heterozygous missense mutation in the SOD1 gene, which resulted in an amino acid substitution of isoleucine 149 by threonine. Hoarseness can be the initial symptom of ALS. Therefore, in cases of bilateral vocal cord paralysis of unknown etiology, ALS should be taken into consideration.

Protein aggregation and protein instability govern familial amyotrophic lateral sclerosis patient survival

The nature of the "toxic gain of function" that results from amyotrophic lateral sclerosis (ALS)-, Parkinson-, and Alzheimer-related mutations is a matter of debate. As a result no adequate model of any neurodegenerative disease etiology exists. We demonstrate that two synergistic properties, namely, increased protein aggregation propensity (increased likelihood that an unfolded protein will aggregate) and decreased protein stability (increased likelihood that a protein will unfold), are central to ALS etiology. Taken together these properties account for 69% of the variability in mutant Cu/Zn-superoxide-dismutase-linked familial ALS patient survival times. Aggregation is a concentration-dependent process, and spinal cord motor neurons have higher concentrations of Cu/Zn-superoxide dismutase than the surrounding cells. Protein aggregation therefore is expected to contribute to the selective vulnerability of motor neurons in familial ALS.

SOD1 mutations disrupt redox-sensitive Rac regulation of NADPH oxidase in a familial ALS model

Neurodegeneration in familial amyotrophic lateral sclerosis (ALS) is associated with enhanced redox stress caused by dominant mutations in superoxide dismutase-1 (SOD1). SOD1 is a cytosolic enzyme that facilitates the conversion of superoxide (O(2)(*-)) to H(2)O(2). Here we demonstrate that SOD1 is not just a catabolic enzyme, but can also directly regulate NADPH oxidase-dependent (Nox-dependent) O(2)(*-) production by binding Rac1 and inhibiting its GTPase activity. Oxidation of Rac1 by H(2)O(2) uncoupled SOD1 binding in a reversible fashion, producing a self-regulating redox sensor for Nox-derived O(2)(*-) production. This process of redox-sensitive uncoupling of SOD1 from Rac1 was defective in SOD1 ALS mutants, leading to enhanced Rac1/Nox activation in transgenic mouse tissues and cell lines expressing ALS SOD1 mutants. Glial cell toxicity associated with expression of SOD1 mutants in culture was significantly attenuated by treatment with the Nox inhibitor apocynin. Treatment of ALS mice with apocynin also significantly increased their average life span. This redox sensor mechanism may explain the gain-of-function seen with certain SOD1 mutations associated with ALS and defines new therapeutic targets.

A novel SOD1 gene mutation in a Korean family with amyotrophic lateral sclerosis

BACKGROUND

Superoxide dismutase 1 (SOD1) gene mutations are responsible for approximately 20% of all familial amyotrophic lateral sclerosis (ALS) cases. However, these cases, especially those with SOD1 gene mutations, have not been reported in Korea.

OBJECTIVES

The SOD1 gene in Korean family with ALS was screened for potential mutations and the clinical data was collected.

MATERIALS AND METHODS

The clinical histories and neurological findings of the family members were obtained. Genomic DNA was isolated from the leukocytes of whole blood samples and the coding region of the SOD1 gene was analyzed by PCR and sequencing.

RESULTS

The family with ALS showed a novel missense mutation in the SOD1 gene, which was heterozygous for the mutation, GGC to GTT, causing the substitution of valine for glycine at codon 10 (Gly10Val) in exon 1. Clinically, the patients exhibited early onset and rapid disease progression.

CONCLUSIONS

Familial ALS with a novel Gly10Val mutation in the SOD1 gene showed severe clinical features. The mutation lies in a region involved in a dimer contact in the three-dimensional structure of the SOD1 protein. This study expands the number of ALS-associated SOD1 gene mutations.

Amyotrophic lateral sclerosis: copper/zinc superoxide dismutase (SOD1) gene mutations

Mutations of the SOD1 gene, encoding the enzyme copper/zinc superoxide dismutase, have been identified in around 20% of patients with familial amyotrophic lateral sclerosis (ALS), and also in patients with apparently sporadic ALS. The table documents the mutations identified and published to date, and references clinical and pathological descriptions of the patients and families with individual mutations. The table includes 63 different mutations of SOD1 at 43 codons, three intronic sites, and two in the 3' untranslated region. Most of the mutations are heterozygotes, with autosomal dominant inheritance, but a small number of individuals appear to be sporadic, or are homozygotes with autosomal dominant recessive inheritance.