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

Randomized, double-blind, placebo-controlled trial of arimoclomol in rapidly progressive SOD1 ALS

Objective

To examine the safety and tolerability as well as the preliminary efficacy of arimoclomol, a heat shock protein co-inducer that promotes nascent protein folding, in patients with rapidly progressive SOD1 amyotrophic lateral sclerosis (ALS).

Methods

This was a double-blind, placebo-controlled trial in which patients with rapidly progressive SOD1-mutant ALS were randomized 1:1 to receive arimoclomol 200 mg tid or matching placebo for up to 12 months. Study procedures were performed using a mix of in-person and remote assessments. Primary outcome was safety and tolerability. Secondary outcome was efficacy, with survival as the principal measure. Additional efficacy measures were the rates of decline of the Revised ALS Functional Rating Scale (ALSFRS-R) and percent predicted forced expiratory volume in 6 seconds (FEV6), and the Combined Assessment of Function and Survival (CAFS).

Results

Thirty-eight participants were randomized. Thirty-six (19 placebo, 17 arimoclomol) were included in the prespecified intent-to-treat analysis. Apart from respiratory function, groups were generally well-balanced at baseline. Adverse events occurred infrequently, and were usually mild and deemed unlikely or not related to study drug. Adjusting for riluzole and baseline ALSFRS-R, survival favored arimoclomol with a hazard ratio of 0.77 (95% confidence interval [CI] 0.32–1.80). ALSFRS-R and FEV6 declined more slowly in the arimoclomol group, with treatment differences of 0.5 point/month (95% CI −0.63 to 1.63) and 1.24 percent predicted/month (95% CI −2.77 to 5.25), respectively, and the CAFS similarly favored arimoclomol.

Conclusions

This study provides Class II evidence that arimoclomol is safe and well-tolerated at a dosage of 200 mg tid for up to 12 months. Although not powered for therapeutic effect, the consistency of results across the range of prespecified efficacy outcome measures suggests a possible therapeutic benefit of arimoclomol.

Clinicaltrials.gov identifier

NCT00706147.

Classification of evidence

This study provides Class II evidence that arimoclomol is safe and well-tolerated at a dosage of 200 mg tid for up to 12 months. The study lacked the precision to conclude, or to exclude, an important therapeutic benefit of arimoclomol.

Rapid Progression of Sporadic ALS in a Patient Carrying SOD1 p.Gly13Arg Mutation

Amyotrophic lateral sclerosis (ALS), the most common adult onset motor neuron disease, is pathologically characterized by progressive loss of the upper and lower motor neurons. Mutations in the Cu/Zn superoxide dismutase gene (SOD1) account for about 20% of familial ALS cases and a small percentage of sporadic ALS (SALS) cases, and have revealed a validated genotype-phenotype correlation. Herein, we report a p.Gly13Arg mutation in SOD1 exon 1 in a patient with SALS who presented with a rapidly progressive course, predominantly affecting the lower motor neurons. A 48-year-old man presented with progressive weakness and muscle atrophy of the left upper and lower limbs, followed by muscle fasciculation and cramping. The clinical features of the patient were clearly suggestive of ALS, and implied a sporadic form with rapid progression, predominantly affecting the lower motor neurons. Sequencing of the SOD1 gene by PCR revealed a missense mutation of G to C (c.37G>C) in exon 1, and amino acid substitution of glycine by arginine (p.Gly13Arg). This is the first case identifying the p.Gly13Arg mutation of SOD1 in the Korean population, and clinical assessments of this patient revealed a different phenotype compared with other cases.

Polymerase ζ Activity Is Linked to Replication Timing in Humans: Evidence from Mutational Signatures

Replication timing is an important determinant of germline mutation patterns, with a higher rate of point mutations in late replicating regions. Mechanisms underlying this association remain elusive. One of the suggested explanations is the activity of error-prone DNA polymerases in late-replicating regions. Polymerase zeta (pol ζ), an essential error-prone polymerase biased toward transversions, also has a tendency to produce dinucleotide mutations (DNMs), complex mutational events that simultaneously affect two adjacent nucleotides. Experimental studies have shown that pol ζ is strongly biased toward GC→AA/TT DNMs. Using primate divergence data, we show that the GC→AA/TT pol ζ mutational signature is the most frequent among DNMs, and its rate exceeds the mean rate of other DNM types by a factor of approximately 10. Unlike the overall rate of DNMs, the pol ζ signature drastically increases with the replication time in the human genome. Finally, the pol ζ signature is enriched in transcribed regions, and there is a strong prevalence of GC→TT over GC→AA DNMs on the nontemplate strand, indicating association with transcription. A recurrently occurring GC→TT DNM in HRAS and SOD1 genes causes the Costello syndrome and amyotrophic lateral sclerosis correspondently; we observe an approximately 1 kb long mutation hotspot enriched by transversions near these DNMs in both cases, suggesting a link between these diseases and pol ζ activity. This study uncovers the genomic preferences of pol ζ, shedding light on a novel cause of mutational heterogeneity along the genome.

Slowly progressing lower motor neuron disease caused by a novel duplication mutation in exon 1 of the SOD1 gene

Familial amyotrophic lateral sclerosis accounts for about 5% of all cases of the neurodegenerative disorder amyotrophic lateral sclerosis. Genetic mutations in Cu/Zn superoxide dismutase (SOD1) have been associated with one kind of familial amyotrophic lateral sclerosis (ALS1). We identified a novel duplication mutation in exon 1 of the SOD1 gene in a Japanese family whose members had lower motor neuron diseases. The patients showed slow disease progression, with the onset of lower limb muscle weakness and exertional dyspnea. Some patients had mild motor and sensory neuropathy and/or bladder dysfunction, which is further evidence that SOD1 mutation results in a predominantly lower motor neuron phenotype.

Distinctive clinicopathological features of 2 large families with amyotrophic lateral sclerosis having L106V mutation in SOD1 gene

A clinicopathological study of 2 families with familial amyotrophic lateral sclerosis was previously reported [1]. The present study continues to investigate these families, with detailed clinical, genetic, and neuropathological studies performed on 24 patients, including 5 autopsy cases of the families. A point mutation at codon 106 (L106V) in the copper/zinc superoxide dismutase-1 (SOD1) gene was identified in the families. Average age at onset was 52.0 ± 9.4 years, and initial symptoms were weakness and atrophy in the distal muscles of the lower extremities in most patients. Half of the patients showed neurogenic bladder (overactive bladder) and sensory impairment. The neurophysiological study showed peripheral/central conduction delay. Neuropathological examination revealed severe motor neuron loss with many bizarre reactive astrocytes in the spinal anterior horn. SOD1-immunopositive Lewy body-like hyaline inclusions and aggregation of neurofilaments were observed in the surviving anterior horn cells. Degeneration of the corticospinal tract was relatively minor. In addition, slight but diffuse gliosis was identified in the hypothalamus and medial nucleus of thalamus. Neurogenic bladder, sensory impairment, and degeneration of the hypothalamus and thalamus might be specific features in patients with familial amyotrophic lateral sclerosis with L106V mutation in the SOD1 gene.

Screening of the SOD1, FUS, TARDBP, ANG, and OPTN mutations in Korean patients with familial and sporadic ALS

About 5% of amyotrophic lateral sclerosis (ALS) cases are known to be familial (fALS) and mutations in SOD1 and other genes are found in more than 20% of fALS patients and in 2%-4% of apparently sporadic ALS (sALS) cases. However, there are few reports on the proportion of fALS and the frequency of mutations in Korean patients with ALS. We screened mutations in the SOD1, FUS, TARDBP, ANG, and OPTN genes in 258 consecutively enrolled Korean patients with ALS from October 2006 to November 2010. The frequency of fALS was estimated to be 3.5% (9/258), and mutations were identified in 88.9% (8/9) of fALS patients but only in 2.8% (7/249) of sALS patients. Seven fALS and 3 sALS patients had mutations in SOD1 gene while all the others had FUS gene. The proportion of fALS was lower than that reported in Caucasian populations but the frequency of SOD1 gene mutations in Korean fALS patients (77.8%, 7/9) was much higher than that reported in other ethnic groups. These findings might suggest that there is an ethnic difference in the proportion of fALS and the genetic background of ALS.

A novel exon 1 mutation (G10R) in the SOD1 gene in a patient with familial ALS

Mutations in the superoxide dismutase-1 (SOD1) gene have been found in 12-23% of patients with a diagnosis of ALS. Although the mechanism by which mutant SOD1 causes neural death remains elusive, several lines of evidence suggest that ALS is a protein-folding disease. Here we report a novel missense mutation in exon 1 of the SOD1 gene in a 68-year-old female with familial ALS characterized by spinal onset with upper and lower motor neuron signs and early neuroimaging evidence of corticospinal tract involvement. Molecular analysis identified a heterozygous mutation in codon 10, with substitution of a highly conserved glycine with arginine (G10R). Modelling of the mutant SOD1 showed a strong destabilization of the protein secondary structure that could influence the strength of the dimer interface. This property can result in a failure of the protein to fold and generation of toxic intracellular aggregates, suggesting a pathogenic role for the mutation.

Immature copper-zinc superoxide dismutase and familial amyotrophic lateral sclerosis

Mutations in human copper-zinc superoxide dismutase (SOD1) cause an inherited form of amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease, motor neuron disease). Insoluble forms of mutant SOD1 accumulate in neural tissues of human ALS patients and in spinal cords of transgenic mice expressing these polypeptides, suggesting that SOD1-linked ALS is a protein misfolding disorder. Understanding the molecular basis for how the pathogenic mutations give rise to SOD1 folding intermediates, which may themselves be toxic, is therefore of keen interest. A critical step on the SOD1 folding pathway occurs when the copper chaperone for SOD1 (CCS) modifies the nascent SOD1 polypeptide by inserting the catalytic copper cofactor and oxidizing its intrasubunit disulfide bond. Recent studies reveal that pathogenic SOD1 proteins coming from cultured cells and from the spinal cords of transgenic mice tend to be metal-deficient and/or lacking the disulfide bond, raising the possibility that the disease-causing mutations may enhance levels of SOD1-folding intermediates by preventing or hindering CCS-mediated SOD1 maturation. This mini-review explores this hypothesis by highlighting the structural and biophysical properties of the pathogenic SOD1 mutants in the context of what is currently known about CCS structure and action. Other hypotheses as to the nature of toxicity inherent in pathogenic SOD1 proteins are not covered.

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.

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.

Effect of transgene copy number on survival in the G93A SOD1 transgenic mouse model of ALS

Transgenic mice expressing multiple copies of the G93A mutant form of SOD1 develop motor neuron pathology and clinical symptoms similar to those seen in patients with amyotrophic lateral sclerosis (ALS). The phenotype of these mice is dependent on the number of transgene copies in their genome. Changes in transgene copy number, although rare, can sometimes occur while mating due to intra locus recombination events during meiosis. The objective of this study was to develop a real time quantitative PCR method to determine changes in transgene copy number in these mice and to evaluate the effect of transgene copy number on the phenotype of the G93A SOD1 mouse model of ALS.