A novel mutation in Cu/Zn superoxide dismutase gene in Japanese familial amyotrophic lateral sclerosis

A combined clinical and computational approach to understand the SOD1A4T-mediated pathogenesis of rapidly progressive familial amyotrophic lateral sclerosis

Here, we aim to provide a comprehensive clinical and biomolecular description of familial amyotrophic lateral sclerosis (fALS) in a 25-year-old female patient with respect to the SOD1^A4T genotype. The clinical diagnosis of the disease was based on family history, neurological examination, electroneurophysiological studies, and revised El Escorial criteria. The heterozygous presence of the A4T mutation in the proband was confirmed by PCR coupled with Sanger sequencing of exon 1 of the SOD1 gene. The mutation was introduced in silico into the three-dimensional structure of the native protein. After energy minimization and quality assessment, non-covalent interactions around threonine-4 and changes in protein stability were calculated computationally. The patient differed widely in age at onset, initial neurological symptoms and findings, and survival time from her kindred, in which several members are affected. SOD1^A4T-linked fALS in this case had bulbar involvement at onset, a combination of lower and upper motor neuron signs and showed rapid progression. Unlike alanine-4, threonine-4 failed to engage in hydrophobic interactions with the vicinal non-polar amino acids. The overall fold of the modeled SOD1^A4T mutant remained intact, but unfolding free energy estimations disclosed a decrease in the protein's stability. We report a phenotypically distinct patient with fALS due to the SOD1^A4T mutation and further expand the largest pedigree ever published for SOD1^A4T-linked fALS. Genotype‒phenotype correlation in fALS is complex, and it demands detailed clinical investigation and advanced scientific research. Awareness of the broadened phenotypic spectrum might potentially enhance the diagnosis and genetic counseling of fALS.

Identification of an A4V SOD1 mutation in a Chinese patient with amyotrophic lateral sclerosis without the A4V founder effect common in North America

We identified a missense alanine to valine mutation at codon 4 (A4V) in the Cu/Zn superoxide dismutase (SOD1) gene in a 51-year-old male of Chinese origin with familial amyotrophic lateral sclerosis (ALS). The patient displayed a typical A4V-related phenotype that included rapid progression and predominant lower motor neuron involvement. This patient is the first such carrier reported outside Caucasian ALS patients, despite the fact that A4V mutations account for up to 50% of all SOD1 mutations in North America. Further SNP analyses showed that the A4V patient of Chinese origin did not share the common founder effect observed in North America.

A clinical variance in familial amyotrophic lateral sclerosis with a point mutation in Cu/Zn superoxide dismutase gene

We report here a novel point mutation in exon 5 of the Cu/Zn superoxide dismutase (SOD) gene resulting in an amino acid substitution of valine(148) by isoleucine (V148I) in a Japanese family with amyotrophic lateral sclerosis (FALS). In this family, the age at onset was young (28.0 ± 3.8 years old, mean ± SD, n = 4) and the disease progression was rapid (22.0 ± 5.9 months, n = 3) with low Cu/Zn SOD activity (56.3 and 59.0% of the controls, n = 2). It is interesting that the clinical features of ALS varied very much among the affected members. One case had weakness of the lower extremities at first, and died without bulbar paresis. The second case first noticed wasting of the upper limbs with bulbar symptoms, but the third had weakness of upper extremities without developing dysarthria nor dysphagia until death. The living remainder first developed fasciculation of the tongue without weakness of extremities. The valine(148) is conserved among different species, and V148I mutation might destabilize dimer formation with another SOD subunit, leading to decrease enzymatic activity. These results suggested that there could be considerable clinical variance among the patients of FALS within one family, carrying the same Cu/Zn SOD mutation such as V148I.

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.

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.

TDP-43 immunoreactivity in neuronal inclusions in familial amyotrophic lateral sclerosis with or without SOD1 gene mutation

Recently, 43-kDa TAR DNA-binding protein (TDP-43) was identified as a component of ubiquitinated inclusions (UIs) in sporadic amyotrophic lateral sclerosis (SALS). To clarify whether TDP-43 immunoreactivity is present in neuronal inclusions in familial ALS (FALS), we examined immunohistochemically the brains and spinal cords from four cases of FALS, two with Cu/Zn superoxide dismutase (SOD1) gene mutation and two without, together with three cases of SALS and three control subjects, using two antibodies, one polyclonal and one monoclonal, against TDP-43. Neuropathologically, the SOD1-related FALS cases were characterized by Lewy body-like hyaline inclusions (LBHIs) in the lower motor neurons. On the other hand, the SOD1-unrelated FALS cases showed degeneration restricted to the upper and lower motor neuron systems, with Bunina bodies (BBs) and UIs in the lower motor neurons, being indistinguishable from SALS. No cytoplasmic TDP-43 immunoreactivity was observed in the control subjects or SOD1-related FALS cases; LBHIs were ubiquitinated, but negative for TDP-43. UIs observed in the SALS and SOD1-unrelated FALS cases were clearly positive for TDP-43. BBs were negative for this protein. Interestingly, in these SALS and FALS cases, glial cells were also found to have cytoplasmic TDP-43-positive inclusions. These findings indicate that the histological and molecular pathology of SALS can occur as a phenotype of FALS without SOD1 mutation.

Familial amyotrophic lateral sclerosis: a SOD1-unrelated Japanese family of bulbar type with Bunina bodies and ubiquitin-positive skein-like inclusions in lower motor neurons

We describe a new family with adult onset amyotrophic lateral sclerosis (FALS), in which the disease was characterized clinically by relatively rapid progression of bulbar symptoms. Gene analysis of Cu/Zn superoxide dismutase (SOD1) performed in one patient showed no mutations. Autopsy of another patient demonstrated degenerative changes restricted to the upper and lower motor neuron systems; no evident changes were observed in the posterior column, Clarke's column or spinocerebellar tracts. The presence of Bunina bodies and ubiquitin-positive skein-like inclusions in the lower motor neuron was of considerable interest. Cases of FALS with such pathological features are quite rare in the literature. Identification of the gene responsible for the disease is desirable in order to shed further light on the molecular pathology of not only familial, but also sporadic, ALS.

Is motoneuronal cell death in amyotrophic lateral sclerosis apoptosis?

To clarify the controversy concerning whether the cell death of motor neurons in ALS is apoptosis, we investigated the expression of Apaf-1 and caspase-9 mRNA in spinal cord tissue obained at autopsy from patients with ALS and controls using RT-PCR; the presence of in situ nuclear DNA fragmentation in motor neurons by the TdT-mediated dUTP-biotin nick end-labeling (TUNEL) method; and immunocytochemical localization of Apaf-1 and caspase-3, which are known as promotors of apoptotic processes. Although Apaf-1 and caspase-9 mRNAs levels were increased in ALS, Apaf-1 immunoreactivity (IR) showed no significant difference between ALS and the control, and caspase-3 IR was not observed in ALS motoneurons, casting doubt on the notion that motor neurons in ALS undergo death by the classic apoptotic pathway. Although TUNEL-positive motor neurons were frequently observed in the anterior horn in ALS, these neurons always showed an atrophic cell body with a shrunken and pyknotic nucleus, indicating that they were at the terminal stage of degeneration. No apoptotic bodies were seen. These findings suggest that the mechanism of motor neuronal cell death in ALS might not be apoptosis, but some other as yet unidentified mechanism.

Coexpression of yeast copper chaperone (yCCS) and CuZn-superoxide dismutases in Escherichia coli yields protein with high copper contents

To fully understand the function of the Cu- and Zn-containing superoxide dismutases in normal and disordered cells, it is essential to study protein variants with full metal contents. We describe the use of an Escherichia coli-based expression system for the overproduction of human intracellular wild type CuZn-superoxide dismutase (SOD), the CuZnSOD variant F50E/G51E (monomeric), two amyotrophic lateral sclerosis-related mutant CuZnSOD variants (D90A and G93A), and PseudoEC-SOD, all with high Cu contents. This system is based on coexpression of the SOD variants with the yeast copper chaperone yCCS during growth in a medium supplemented with Cu(2+) and Zn(2+). The recombinant SOD enzymes were all found in the cytosol and represented 30-50% of the total bacterial protein. The enzymes were purified to homogeneity and active enzymes were obtained in high yield. The resulting proteins were characterized through immunochemical reactivity and specific activity analyses, in conjunction with mass-, photo-, and atomic absorption-spectroscopy.

Familial amyotrophic lateral sclerosis with bulbar onset and a novel Asp101Tyr Cu/Zn superoxide dismutase gene mutation

We describe a patient with familial amyotrophic lateral sclerosis (FALS) in whom we identified a novel missense mutation in exon 4 (Asp101Tyr) of the Cu/Zn superoxide dismutase (SOD1) gene. The disease started with a bulbar symptom (rapidly progressive hoarseness) and at autopsy showed degenerative changes restricted to the upper and lower motor neuron systems (more strictly, with lower motor predominance, showing the most severe degeneration in the nucleus ambiguus). Occasional intracytoplasmic Lewy-body-like hyaline inclusions that were immunoreactive for ubiquitin and SOD1, but immunonegative for neurofilament protein, were found in the lower motor neurons. This is the first report of hoarseness as the initial manifestation of FALS. This SOD1 gene mutation may be associated with a particular clinicopathological phenotype.

A4T mutation in the SOD1 gene causing familial amyotrophic lateral sclerosis

We report the clinical and laboratory findings in the largest kindred so far recorded with familial amyotrophic lateral sclerosis due to an A4T mutation in the SOD1 gene. The age of onset ranged from 32 to 60 years, with a mean of 46 years. Weakness in the legs was the most frequent early symptom and there was a predominance of lower motor neuron signs. The mean time from onset of symptoms to death was 14 months. One man with onset at the age of 37 has shown a slowly developing form and is currently alive 76 months after diagnosis (October 2002), although severely affected. The A4T mutation, with one exception, was of similar severity to the A4V mutation.

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.

Gain in functions of mutant Cu,Zn-superoxide dismutases as a causative factor in familial amyotrophic lateral sclerosis: less reactive oxidant formation but high spontaneous aggregation and precipitation

Eight mutant Cu,Zn-superoxide dismutases (SODs) related to familial amyotrophic lateral sclerosis (FALS) were produced in a baculovirus/insect cell expression system and their molecular properties in terms of hydroxyl radical formation and aggregation were compared with the wild-type enzyme. Treatment of the enzymes with Chelex 100 resin decreased Cu contents as well as SOD activities in all mutant Cu,Zn-SODs, indicating that the affinities of the enzymes for copper ion were decreased. Contrary to previous reports, all the mutant Cu,Zn-SODs exhibited less reactive oxidant producing ability in the presence of hydrogen peroxide than the wild-type enzyme. Both SOD activities and their reactive oxidant forming correlated well with the copper ion content of the molecules. In addition, the proteins spontaneously aggregated and were precipitated by simple centrifugation at 12,000g for 20 min in keeping their enzyme activities. Since hyaline inclusions found in FALS patients with SOD1 mutations contained components which were reactive to anti-Cu,Zn-SOD antibody, a primary reaction caused by mutant SOD1 may be attributed to their propensity to form aggregates. Aggregated but still active mutant SOD1 would be expected to mediate the formation of reactive oxygen species and nitrosylation in a more condensed state.

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.

A novel mutation (Cys6Gly) in the Cu/Zn superoxide dismutase gene associated with rapidly progressive familial amyotrophic lateral sclerosis

Autosomal-dominant familial amyotrophic lateral sclerosis (FALS) is associated with mutation in the gene that encodes Cu/Zn superoxide dismutase (SOD1). We identified a novel missense mutation of SOD-1 (Cys6Gly) in exon 1 in a Japanese woman and her family. The illness showed rapid progression similarly to the FALS with a mutation of Cys6Phe that was reported by Morita et al. (1996) (Morita, M., Aoki, M., Abe, K., Hasegawa, T., Sakuma, R., Onodera, Y., Ichikawa, N., Nishizawa, M. and Itoyama, Y., A novel two-base mutation in the Cu/Zn superoxide dismutase gene associated with familial amyotrophic lateral sclerosis in Japan. Neurosci. Lett., 205 (1996) 79-82). Mutation of the cystein at amino acid 6 might be associated with the rapid progression of ALS.

Abnormalities of protein kinases in neurodegenerative diseases

In neurodegenerative diseases such as ALS and AD there is evidence for abnormal regulation of protein kinases. In these diseases, altered activities and protein levels of several specific kinases suggest that abnormal phosphorylation is present and this aberrant phosphorylation may be involved in the pathogenesis of these diseases. The observation that regulation of the NMDA receptor ion channel is altered in tissue from ALS patients may arise from the abnormal phosphorylation state of the protein kinase regulating NMDA receptor function. Whether the abnormalities of these protein kinases is a primary event leading to altered receptor regulation or vice versa is still poorly understood. The seemingly multiple pathogenic mechanisms of ALS and AD create complexity in assessing a primary cause that may lead to cell death. The mechanisms causing cell death (apoptosis or necrosis) may be overlapping with integrated events among the components interacting and contributing to a final pathway for neuron death. Thus, evidence of impairment in protein kinase signalling in these diseases may be a primary cause, a secondary event, or a compensatory mechanism. To further study this issue, different model systems could be beneficial to obtain a better understanding of these diseases.

Molecular analyses of the Cu/Zn superoxide dismutase gene in patients with familial amyotrophic lateral sclerosis (ALS) in Japan

1. Amyotrophic lateral sclerosis (ALS) is a degenerative disorder characterized by selective damage to the neural system that mediates voluntary movement. Although the pathophysiologic process of ALS remains unknown, about 5 to 10% of cases are familial. According to genetic linkage studies, the familial ALS (FALS) gene has been mapped on chromosome 21 in some families and recent work identified some different missense mutations in the Cu/Zn superoxide dismutase gene in FALS families. 2. We recently identified five mutations in six FALS families. The mutations identified in our FALS families are H46R, L84V, I104F, S134N, and V148I. The H46R mutation that locates in the active site of Cu/Zn SOD gene is associated with two Japanese families with very slow progression of ALS. On the other hand, the L84V mutation associated with a rapidly progressive loss of motor function with predominant lower motor neuron manifestations. 3. In the family with the V148I, the phenotype of the patient varied very much among the affected members. One case had weakness of the lower extremities at first and died without bulbar paresis. The second case first noticed wasting of the upper limbs with bulbar symptoms, but the third had weakness of upper extremities without developing dysarthria nor dysphagia until death. These mutations account for 50% of all FALS families screened, although Cu/Zn SOD gene mutations are responsible for less than about 13-21% in the Western population. 4. Our results indicate that the progression of disease with mutations of Cu/Zn SOD is well correlated with each mutation. The exact mechanism by which the abnormal Cu/Zn SOD molecules selectively affect the function of motor neurons is still unknown.

Formation of granular cytoplasmic aggregates in COS7 cells expressing mutant Cu/Zn superoxide dismutase associated with familial amyotrophic lateral sclerosis

To investigate the molecular mechanisms of the 'gain of toxic function' of mutant Cu/Zn superoxide dismutase (SOD) associated with familial amyotrophic lateral sclerosis (FALS), mutant (Ala 4 --> Thr, Gly 85 --> Arg, Gly 93 --> Ala, and two base-pair deletion in the 126th codon), as well as wild-type (wt), Cu/Zn SODs were expressed in COS7 cells. The formation of granular cytoplasmic aggregates accompanied by collapse of the cytoplasm was observed in cells expressing mutant (mt) Cu/Zn SODs, but not in cells expressing wt Cu/Zn SOD. The aggregates contained ribosome-like particles and endoplasmic reticulum. These results suggest the possibility that mt Cu/Zn SODs promote the formation of aggregates which are toxic to cells.

Oxidative stress and superoxide dismutase in development, aging and gene regulation

Free radicals and other reactive oxygen species are produced in the metabolic pathways of aerobic cells and affect a number of biological processes. Oxidation reactions have been postulated to play a role in aging, a number of degenerative diseases, differentiation and development as well as serving as subcellular messengers in gene regulatory and signal transduction pathways. The discovery of the activity of superoxide dismutase is a seminal work in free radical biology, because it established that free radicals were generated by cells and because it made removal of a specific free radical substance possible for the first time, which greatly accelerated research in this area. In this review, the role of reactive oxygen in aging, amyotrophic lateral sclerosis (a neurodegenerative disease), development, differentiation, and signal transduction are discussed. Emphasis is also given to the role of superoxide dismutases in these phenomena.

Epidemiology of motor neuron disease in the Kii Peninsula of Japan, 1989-1993: active or disappearing focus?

During the period 1989-1993, the incidence and migration patterns of patients with motor neuron diseases (MND) in Wakayama Prefecture, including one of the high-incidence Kii Peninsula foci ('Kozagawa focus'), were surveyed to determine whether the focus had truly disappeared or not. Overall, the crude average annual incidence was 1.43 per 100000 population; when age-adjusted to the 1990 Japanese population, it was 1.25 (1.85 for males and 0.61 for females). The average annual age- and sex-specific incidence steadily increased to a peak between 60 and 69 years and dropped after 70. Geographically, the rates varied in the five regions of Wakayama Prefecture from 0.38 to 2.48. The areas with high incidence were distributed in the central and southernmost regions; the highest was in the Kozagawa focus with 9.54 (two ALS cases within five years; 4193 base population, 1990). During the study period, four emigrants from Kozagawa had developed MND one to four decades after leaving the focus. Although the remarkable clustering of MND was thought to have disappeared, the southern Kii Peninsula remains a high-risk area for MND, especially if one interprets the data so as to include the emigrants. In general, the age at onset has increased in the past 20 years from 56.5 to 61.7; male predominance is observed.

Clinical and molecular analysis of neurodegenerative diseases

Clinical and molecular analyses of neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and spinocerebellar ataxia type 1 (SCA1) were performed. In the present study, a Japanese family of AD with an Ala285Val substitution in exon 8 of the presenilin-1 (PS-1) gene was found. This family was characterized by relatively late onset (mean age at 50 years) in familial AD with PS-1 gene mutation and by absence of myoclonus, seizure or paratonia. Magnetic resonance image (MRI) study showed marked linear signal abnormalities in white matter of parietoocctipital lobes, suggesting a presence of cortical amyloid angiopathy of the patient with PS-1 gene mutation. Clinical characteristics of familial amyotrophic lateral sclerosis (FALS) with four different missense point mutations in exons 2, 4, and 5 of the Cu/Zn superoxide dismutase (SOD) gene were reported. Although features of progressive neurogenic muscular atrophy was common in patients of these families, patients of each family showed characteristic clinical features. Although lower motor sign was evident in all cases, hyperreflexia varied from 0 to 100% among patients with the different mutations, and Babinski sign was not observed in any cases. Bulbar palsy was frequent with a mutation, but not present with another mutation. SOD activity of red blood cells was generally reduced with minor variations. CAG trinucleotide repeat expansion was analyzed in 25 families with hereditary ataxia of Menzel type in the northeast of Japan. Twenty of 38 patients in 12 families had expanded allele for spinocerebellar ataxia type 1 (SCA1). Study of the number of CAG repeats in various tissues showed no differences in the repeat length in lymphocytes, muscle or brain; sperm, however, showed an obvious expansion. This may be a clue to a possible mechanism for the molecular basis of paternal anticipation of the disease. These results suggest that clinical features of some familial cases of neurodegenerative diseases such as AD, ALS, and SCA1 are well correlated with their genetic mutations.

Familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is sporadic in ninety percent of cases and familial (FALS) in ten percent. Both forms of FALS whether transmitted as an autosomal dominant (DFALS) or as an autosomal recessive (RFALS) trait is genetically heterogeneous. The locus for one form of RFALS maps to chromosome 2q33. Fifteen percent of DFALS families have mutations in the gene for Cu, Zn superoxide dismutase (SOD1) gene which is coded on chromosome 21. These mutations result in decreased SOD1 activity and shortened half-life of the protein in most instances. Transgenic mice overexpressing mutated SOD1 protein develop an ALS-like disease which suggests that the degeneration of motor neurons in DFALS is caused by the gain of a novel toxic function by mutated SOD1 rather than by the decrease of SOD1 activity. Possible mechanisms of the novel neurotoxic function of mutated SOD1 are discussed.

Cu/Zn superoxide dismutase gene mutations in amyotrophic lateral sclerosis: correlation between genotype and clinical features

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Ferrocene-oligonucleotide conjugates for electrochemical probing of DNA

Toward the development of a universal, sensitive and convenient method of DNA (or RNA) detection, electrochemically active oligonucleotides were prepared by covalent linkage of a ferrocenyl group to the 5'-aminohexyl-terminated synthetic oligonucleotides. Using these electrochemically active probes, we have been able to demonstrate the detection of DNA and RNA at femtomole levels by HPLC equipped with an ordinary electrochemical detector (ECD) [Takenaka,S., Uto,Y., Kondo,H., Ihara,T. and Takagi,M. (1994) Anal. Biochem., 218, 436-443]. Thermodynamic and electrochemical studies of the interaction between the probes and the targets are presented here. The thermodynamics obtained revealed that the conjugation stabilizes the triple-helix complexes by 2-3 kcal mol-1 (1-2 orders increment in binding constant) at 298 K, which corresponds to the effect of elongation of additional several base triplets. The main cause of this thermodynamic stabilization by the conjugation is likely to be the overall conformational change of whole structure of the conjugate rather than the additional local interaction. The redox potential of the probe was independent of the target structure, which is either single- or double stranded. However, the potential is slightly dependent (with a 10-30 mV negative shift on complexation) on the extra sequence in the target, probably because the individual sequence is capable of contacting or interacting with the ferrocenyl group in a slightly different way from each other. This small potential shift itself, however, does not cause any inconvenience on practical applications in detecting the probes by using ECD. These results lead to the conclusion that the redox-active probes are very useful for the microanalysis of nucleic acids due to the stability of the complexes, high detection sensitivity and wide applicability to the target structures (DNA and RNA; single- and double strands) and the sequences.

Three novel mutations and two variants in the gene for Cu/Zn superoxide dismutase in familial amyotrophic lateral sclerosis

Autosomal dominant inheritance is exhibited by about 10% of cases of amyotrophic lateral sclerosis (ALS), a paralytic disorder characterized by the death of motor neurons in the brain and spinal cord. A subgroup of these familial cases are linked to mutations in the gene which codes for Cu/Zn superoxide dismutase (SOD1). We report three additional mutations occurring in the SOD1 gene in ALS patients and two single base pair variant changes. The single base pair change in an ALS family causes a glycine 93 to valine substitution, which is the fifth distinct amino acid change reported for the glycine 93 residue. One missense mutation in exon 5 would substitute neutral valine for the negatively-charged aspartate 124 (aspartate 124 to valine). An individual with an apparently sporadic case of ALS carries a three base pair deletion in exon 5 of the SOD1 gene. These three mutations bring to 38 the total number of distinct SOD1 mutations associated with familial ALS.

Genetics of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a paralytic disorder caused by degeneration of motor neurons in the brain and spinal cord. Identification of mutations in the gene for Cu,Zn superoxide dismutase (SOD1) in a subset of ALS families made it possible to develop a transgenic mouse model of ALS and to investigate its pathogenesis. These investigations suggest that mutant SOD1 acts through a toxic gain of function which may involve generation of free radicals. Conformational change in the mutant SOD1 protein, especially the distortion of the 'rim' of the electrostatic guidance channel may be central to this toxic gain of function and to the pathogenesis of ALS.

Instability of mutant Cu/Zn superoxide dismutase (Ala4Thr) associated with familial amyotrophic lateral sclerosis

In about 20-25% of cases of familial amyotrophic lateral sclerosis (FALS) patients have mutations in the Cu/Zn superoxide dismutase (SOD1) gene. The mechanism through which the mutations in the SOD1 gene cause ALS still remain unknown. We performed pulse-chase experiments using a system for the transient expression of human SOD1 in COS7 cells to examine whether the Ala4Thr mutation, which we previously reported, decreases the stability of SOD1. The expression vector (pEF-BOS) carrying the wild-type or mutant (Ala4Thr) human SOD1 cDNA was transfected into COS7 cells, and transiently expressed human SOD1 was then metabolically radiolabeled. Half-lives of the wild-type and the Ala4Thr mutant SOD1 were determined to be 78 h and 18 h, respectively. These results suggest that the Ala4Thr mutation in SOD1 decreases the stability of SOD1 and that this instability may play an important role in the pathogenesis of the degeneration of motor neurons in FALS.

Clinical characteristics of familial amyotrophic lateral sclerosis with Cu/Zn superoxide dismutase gene mutations

We report clinical characteristics of familial amyotrophic lateral sclerosis (FALS) with 4 different missense point mutations in exons 2, 4, and 5 of the Cu/Zn superoxide dismutase (SOD) gene, that result in amino acid substitutions of histidine46 by arginine (H46R), leucine84 by valine (L84V), isoleucine104 by phenylalanine (I104F), and valine148 by isoleucine (V148I), in 5 Japanese families. Although features of progressive neurogenic muscular atrophy were common in patients of these families, patients of each family showed characteristic clinical features. FALS patients with the H46R mutation showed a benign clinical course and stereotype progression of muscular weakness and atrophy beginning from the legs. In FALS with the L84V mutation, while the clinical course of the disease was similar, the age at onset was younger in men than women. The patients with I104F showed wide ranges of age at onset and duration with ophthalmoparesis and sensory involvement in one patient. Those with the V148I mutation showed younger age at onset and variable first symptoms within the family. Although lower motor sign was evident in all cases, hyperreflexia varied from 0 to 100% among patients with the different mutations, and the Babinski sign was not observed in any case. Bulbar palsy was frequent with I104F, but not with H46R. SOD activity of the red blood cells was severely reduced with I104F and V148I, but was slightly reduced with H46R. These results suggest that familial ALS with different mutations of the Cu/Zn SOD gene each showed clinical characteristics, and that genetic mutations and clinical features are well correlated in familial ALS.

A novel two-base mutation in the Cu/Zn superoxide dismutase gene associated with familial amyotrophic lateral sclerosis in Japan

We have identified a novel two-base mutation in exon 1 of the Cu/Zn superoxide dismutase (SOD1) gene (TGC to TTT), which resulted in Cys6 to Phe substitution in a Japanese family with amyotrophic lateral sclerosis (ALS). This is the first case of familial ALS-associated two-base change of the SOD1 gene. Similar to several mutations in exon 1 of the SOD1 gene such as Ala4 to Val, Ala4 to Thr and Val14 to Met, affected members of the present family showed a rapid progression of motor dysfunction. Although Ala4, Cys6 and Val7 reside in the middle of the first beta-strand of the SOD1, a family with a mutation of Val7 to Glu associates with slow progression of the disease. These findings suggest that clinical courses are variable with each mutation, even in the same exon.

Induction of nitrotyrosine-like immunoreactivity in the lower motor neuron of amyotrophic lateral sclerosis

Spinal cords of sporadic cases with amyotrophic lateral sclerosis (ALS) and normal controls were immunohistochemically examined using antibodies for Cu/Zn superoxide dismutase (SOD) and nitrotyrosine (NT). Immunoreactivity for Cu/Zn SOD of the motor neurons was not different between the ALS and controls. In contrast, immunoreactivity for NT was densely detected in motor neurons of ALS but was not or was only minimally detected in those of controls. The staining was also found in the axons of motor neurons of ALS, but was not found in the controls. These results suggest that nitration of protein-tyrosine residue is upregulated in motor neurons of the spinal cord of ALS.

Identification of three novel mutations in the gene for Cu/Zn superoxide dismutase in patients with familial amyotrophic lateral sclerosis

About 10% of cases of amyotrophic lateral sclerosis (ALS), a paralytic disorder characterized by death of motor neurons in the brain and spinal cord, exhibit autosomal dominant inheritance. A subgroup of these familial cases are caused by mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). We report here three additional mutations occurring in the SOD1 gene in three families with ALS. Two of these changes are missense mutations in exon 5 of the SOD1 gene, resulting in leucine 144 to serine and alanine 145 to threonine substitutions. The third, a single base pair change in intron 4 immediately upstream of exon 5, results in an alternatively spliced mRNA. The alternate transcript conserves the open reading frame of exon 5, producing an SOD1 protein with three amino acids inserted between exons 4 and 5 (following residue 118). These three mutations bring to 29 the total number of distinct SOD1 mutations associated with familial ALS.

Decreased thermal stability of red blood cell glu100-->gly superoxide dismutase from a family with amyotrophic lateral sclerosis

Familial amyotrophic lateral sclerosis is a degenerative motor neuron disease associated in some cases with the presence of a mutant form of Cu/Zn superoxide dismutase. We have studied the stability of the gly100-->glu mutant in extracts of red cells obtained from members of a family with a history of the disease. Extracts containing the mutant had an average 68% of normal superoxide dismutase activity. On heating at 65 degrees C, these extracts lost activity at twice the rate of extracts containing only the normal enzyme. Decreased heat stability was also evident on native polyacrylamide gel electrophoresis with activity staining. This showed selective loss of first the mutant homodimer and then the heterodimer of the enzyme. Decreased stability intracellularly could be a factor in motor neuron degeneration.

Variance of age at onset in a Japanese family with amyotrophic lateral sclerosis associated with a novel Cu/Zn superoxide dismutase mutation

Although about 5 to 10% of amyotrophic lateral sclerosis (ALS) cases are familial, the pathophysiology of ALS remains unknown. A new point mutation in exon 4 of the Cu/Zn superoxide dismutase (SOD) gene, resulting in an amino acid substitution of leucine84 by valine (L84V), in a Japanese patient with familial ALS (FALS) was identified. This L84V substitution was not observed in 57 normal Japanese control subjects. The enzymatic activities of Cu/Zn SOD of skin fibroblasts were significantly reduced to 75% of the control level in the affected patient. The progression of the disease with this mutation is very rapid, but the age at onset varies with sex or generation within a family.

Oxidative stress: its role in the pathogenesis of amyotrophic lateral sclerosis

The discovery of mutations in the Cu,Zn superoxide dismutase gene in familial ALS implicates oxidative stress in the pathogenesis of this disorder. Recent findings further suggest that oxidative stress may also be present in the more common sporadic form of the disease. The possible sources of oxidative stress in ALS are reviewed, and the participation of this disease mechanism to motorneuron death is discussed.

Amyotrophic lateral sclerosis associated with homozygosity for an Asp90Ala mutation in CuZn-superoxide dismutase

Recent reports have shown heterozygosity for some twenty different mutations in the CuZn-superoxide dismutase (CuZn-SOD) gene in familial amyotrophic lateral sclerosis (FALS), and analysed samples from patients have shown decreased enzymic activity. Here we report homozygosity for an exon 4 mutation, Asp90Ala in fourteen patients among four unrelated ALS families and four apparently sporadic ALS patients from Sweden and Finland. The erythrocyte CuZn-SOD activity is essentially normal. Our findings suggest that this CuZn-SOD mutation causes ALS by a gain of function rather than by loss, and that the Asp90Ala mutation is less detrimental than previously reported mutations.

Neuropathological changes in two lines of mice carrying a transgene for mutant human Cu,Zn SOD, and in mice overexpressing wild type human SOD: a model of familial amyotrophic lateral sclerosis (FALS)

Two different lines of mice, G1 and G20, carrying a transgene for a mutant form of Cu,Zn SOD, found in a family with familial amyotrophic lateral sclerosis (FALS), develop clinical and pathological changes which are, in their late stages, strikingly similar to those in human disease. We have analyzed the distribution and characteristics of lesions in the central and peripheral nervous systems of such mice. The most affected structure was the spinal cord, followed by the medulla, pons and midbrain. The early stages of the disease were characterized by vascular degeneration of anterior horn neurons and their processes, while, in the late stages, the main changes consisted of neuronal loss and atrophy of the anterior horns and the deposition in these areas of multiple filamentous inclusions resembling Lewy bodies. In the late stages of the disease, the white matter of the spinal cord was also involved, particularly in the anterior and lateral columns. Posterior columns were also involved, but to a much lesser degree. The brainstem structures also showed vacuolar degeneration of several motor nuclei and of several groups neurons in the reticular formation. Anterior roots and peripheral nerves showed the classical features of Wallerian degeneration. The dorsal root ganglia, with rare exceptions, were unremarkable. The posterior roots showed mild changes in the most severely affected mice. Changes in these two affected lines were compared to changes in mice overexpressing wild type, rather than mutant human Cu,Zn SOD. These mice never developed clinical disease, although, pathologically, they developed very mild vacuolar changes in the anterior horns of the spinal cord and in motor axons. This study shows that although simple overexpression of SOD may be injurious to motor neurons, albeit very mildly, the mutant form is necessary to produce both clinical disease and severe pathological changes which, in the chronic stage of the disease, have striking similarities to human familial ALS. A dominant gain of function, therefore, is the most likely pathogenesis of tissue injury induced by mutations in Cu,Zn SOD.

Unique molecular properties of superoxide dismutase from teleost fish skin

A unique Cu,Zn-SOD was found and isolated from plaice Paralichthys olivaceus skin. Surprisingly, the properties of purified fish skin SOD were very different from those of SOD from other sources reported so far. The purified SOD was composed of four same subunits of 16 kDa and the molecular weight of the native SOD was found to be around 65 kDa. The dominant amino acids of the SOD were Ser, Thr, Pro and Glu. Above 70 degrees C, thermostability of the SOD was much lower than that of bovine erythrocyte Cu,Zn-SOD.

Superoxide dismutase 1 subunits with mutations linked to familial amyotrophic lateral sclerosis do not affect wild-type subunit function

Mutations in superoxide dismutase 1 (SOD1) have been linked to familial amyotrophic lateral sclerosis, a dominantly inherited motor neuron disorder of midlife. Because SOD1 is a homodimeric enzyme, dimerization of mutant and wild-type SOD1 subunits could dominantly alter the activity, stability, or localization of wild-type SOD1 subunits. To explore these possibilities, we used transient and stable gene transfection to express high levels of either of two mutant human SOD1 subunits in the presence of limited levels of wild-type mouse and/or human SOD1 subunits. Although both mutant subunits displayed diminished half-lives and free radical scavenging activities, their presence caused no change in the half-life or activity of wild-type SOD1 subunits. Our data indicate that mutant subunits do not dominantly affect the function of wild-type SOD1 subunits. These findings, together with observations that many mutant SOD1 subunits retain significant stability and activity, suggest that motor neuron damage in familial amyotrophic lateral sclerosis is caused by the acquisition of injurious properties by mutant SOD1 subunits.

Motor neuron-astrocyte interactions and levels of Cu,Zn superoxide dismutase in sporadic amyotrophic lateral sclerosis

Copper, zinc superoxide dismutase (SOD1) is involved in neutralizing free radicals within cells, and mutant forms of the enzyme have recently been shown to occur in about 20% of familial cases of amyotrophic lateral sclerosis (ALS). To explore the mechanism of SOD1 involvement in ALS, we have analyzed SOD1 in sporadic ALS using activity assays and immunocyto-chemistry. Analyses of SOD1 activity in washed erythrocytes revealed no difference between 13 ALS cases and 4 controls. Spinal cord sections from 6 ALS cases, 1 primary lateral sclerosis (PLS) case, and 1 control case were stained using three different antibodies to SOD1. Since astrocytes are closely associated with motor neurons, antibodies to glial fibrillary acidic protein (GFAP) and vimentin were used as independent monitors of astrocytes. The principal findings from localizations are: (1) normal motor neurons do not have higher levels of SOD1 than other neurons, (2) there was no detectable difference in SOD1 levels in motor neurons of ALS cases and controls, (3) ALS spinal cord displayed a reduction or absence of SOD1-reactive astrocytes compared to the control and PLS cases, and (4) examination of GFAP-stained sections and morphometry showed that the normal close association between astrocytic processes and motor neuron somata was decreased in the ALS and PLS cases. These results indicate the disease mechanism in sporadic ALS may involve alterations in spinal cord astrocytes.