A large-scale international meta-analysis of paraoxonase gene polymorphisms in sporadic ALS.

BACKGROUND: Six candidate gene studies report a genetic association of DNA variants within the paraoxonase locus with sporadic amyotrophic lateral sclerosis (ALS). However, several other large studies, including five genome-wide association studies, have not duplicated this finding. METHODS: We conducted a meta-analysis of 10 published studies and one unpublished study of the paraoxonase locus, encompassing 4,037 ALS cases and 4,609 controls, including genome-wide association data from 2,018 ALS cases and 2,425 controls. RESULTS: The combined fixed effects odds ratio (OR) for rs662 (PON1 Q192R) was 1.09 (95% confidence interval [CI], 1.02-1.16, p = 0.01); the genotypic OR for RR homozygotes at Q192R was 1.25 (95% CI, 1.07-1.45, p = 0.0004); the combined OR for rs854560 (PON1 L55M) was 0.97 (95% CI, 0.86-1.10, p = 0.62); the OR for rs10487132 (PON2) was 1.08 (95% CI, 0.92-1.27, p = 0.35). Although the rs662 polymorphism reached a nominal level of significance, no polymorphism was significant after multiple testing correction. In the subanalysis of samples with genome-wide data from which population outliers were removed, rs662 had an OR of 1.06 (95% CI, 0.97-1.16, p = 0.22). CONCLUSIONS: In contrast to previous positive smaller studies, our genetic meta-analysis showed no significant association of amyotrophic lateral sclerosis (ALS) with the PON locus. This is the largest meta-analysis of a candidate gene in ALS to date and the first ALS meta-analysis to include data from whole genome association studies. The findings reinforce the need for much larger and more collaborative investigations of the genetic determinants of ALS.

Paraoxonase gene polymorphisms and sporadic ALS.

BACKGROUND: The human paraoxonase (PON) gene family consists of three members, PON1, PON2, and PON3, located adjacent to each other on chromosome 7. PON catalytic activity may be influenced by frequent amino acid variants. Chronic exposure to certain chemicals or to environmental factors causing enhanced lipid peroxidation metabolized by paraoxonases may be a risk factor for sporadic ALS (sALS). OBJECTIVE: The aim of this study was to examine the association between PON1 Q192R, PON1 L55M, and PON2 C311S functional polymorphisms and the risk of sALS in a Polish population. METHODS: The authors included 185 patients with a definite or probable diagnosis of sALS (El Escorial Criteria) and 437 healthy controls of similar age and gender. The paraoxonase polymorphisms were studied by PCR and restriction enzyme digestion. RESULTS: Using logistic regression analyses, the C allele of the C311S polymorphism was associated with sALS in dominant and additive models, whereas the R allele of the Q192R polymorphism was associated with sALS in recessive, additive, and dominant models. The authors compared the distribution of haplotypes between cases and controls. The R-C haplotype was overrepresented among cases (odds ratio 3.44, 95% CI: 1.55 to 7.62, p = 0.002). CONCLUSIONS: Frequent amino acid variants in the paraoxonase 1 and paraoxonase 2 genes are associated with sporadic ALS in a Polish population.

DD genotype of ACE gene is a risk factor for intracerebral hemorrhage.

Genetic factors may play a role in susceptibility to stroke. The angiotensin converting enzyme (ACE) gene is a candidate gene for two phenotypically different types of stroke affecting small perforating arteries: spontaneous intracerebral hemorrhage (SIH) and ischemic stroke due to small vessel disease (SVD). The authors report evidence that ACE gene DD homozygosity of the I/D polymorphism in intron 16 is an independent risk factor for SIH, and not for SVD stroke, in a Polish population.

A gene encoding a putative GTPase regulator is mutated in familial amyotrophic lateral sclerosis 2.

Amyotrophic lateral sclerosis 2 (ALS2) is an autosomal recessive form of juvenile ALS and has been mapped to human chromosome 2q33. Here we report the identification of two independent deletion mutations linked to ALS2 in the coding exons of the new gene ALS2. These deletion mutations result in frameshifts that generate premature stop codons. ALS2 is expressed in various tissues and cells, including neurons throughout the brain and spinal cord, and encodes a protein containing multiple domains that have homology to RanGEF as well as RhoGEF. Deletion mutations are predicted to cause a loss of protein function, providing strong evidence that ALS2 is the causative gene underlying this form of ALS.

Clinical implications of the genetics of ALS and other motor neuron diseases.

Genetic mutations have been identified in the major motor neuron diseases, including ALS, spinal muscular atrophy, bulbospinal muscular atrophy (Kennedy's disease), the hereditary spastic paraplegias, and rarer conditions such as GM2 gangliosidosis (hexosaminidase A deficiency). These include mutations in the SOD1 gene, deletions of the telomeric copy of the SMN gene, expansions of the trinucleotide repeat region in the first exon of the androgen receptor gene, other rare mutations, and diseases where linkage has been established but the gene not identified. Identification of one of these genetic abnormalities will allow specific diagnosis in patients. Because cure is not yet available, presymptomatic testing is seldom indicated; in such cases, careful counseling is appropriate.

Nitrotyrosination contributes minimally to toxicity of mutant SOD1 associated with ALS.

Enhanced production of nitrotyrosine and subsequent protein nitration has been proposed as the mechanism by which mutant SOD1 causes death of motor neurons in a familial form of amyotrophic lateral sclerosis (FALS-1). We have tested this hypothesis in a primary culture model in which mutant human SOD1 was expressed in motor neurons of dissociated spinal cord cultures. Preventing formation of nitrotyrosine by inhibiting nitric oxide synthase rescued cultured motor neurons from excitotoxic death induced by adding glutamate to the culture medium, but failed to significantly delay death of motor neurons expressing the G93A mutant SOD1. The results do not support generation of nitrotyrosine being the predominant lethal gain of function conferred by mutations in SOD1.

Cultured glial cells are resistant to the effects of motor neurone disease-associated SOD1 mutations.

Free radical damage has been implicated in the pathophysiology of motor neurone disease (MND); mutations have been identified in the gene encoding Cu/Zn superoxide dismutase (SOD1). There is evidence that glial cell dysfunction may contribute to motor neurone injury, but the exact role of glial cells in MND has yet to be established. The aim of this study was to determine whether expression of mutant SOD1 affects the response of glia to oxidative stress. Stable C6 glioma cells expressing mutant SOD1 and cortical astrocyte cultures from G93A-SOD1 transgenic mice were exposed to: xanthine/xanthine oxidase; hydrogen peroxide; A23187 and 3-morpholinosydonimine. Cell viability was measured using the 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Neither C6 glioma cells nor cortical astrocytes expressing mutant SOD1 were more susceptible to any of the free radical generating systems compared to control cells. These results suggest that astrocytes are resistant to the toxic effects of mutant SOD1 widely reported for neuronal cells.

Discovery of allelic variants of HOXA1 and HOXB1: genetic susceptibility to autism spectrum disorders.

BACKGROUND: Family studies have demonstrated that the autism spectrum disorders (ASDs) have a major genetic etiologic component, but expression and penetrance of the phenotype are variable. Mice with null mutations of Hoxa1 or Hoxb1, two genes critical to hindbrain development, have phenotypic features frequently observed in autism, but no naturally occurring variants of either gene have been identified in mammals. METHODS: By sequencing regions of genomic DNA of patients with autism spectrum disorders, we detected a substitution variant at HOXA1 and an insertion variant at HOXB1, both in coding regions of the genes. Fifty-seven individuals ascertained for a diagnosis of an ASD, along with 166 of their relatives, were typed for these variants. Two non-ASD populations were typed, and the frequency of the newly identified alleles was determined in all groups. The genotypes of the ASD families were tested for conformation to Hardy-Weinberg proportions and Mendelian expectations for gene transmission. RESULTS: The frequency of the variants was 10-25% in persons of European or African origin. In the ASD families, there was a significant deviation from the HOXA1 genotype ratios expected from Hardy-Weinberg proportions (P = 0.005). Among affected offspring, a significant deviation from Mendelian expectation in gene transmission (P = 0.011) was observed. No statistically significant effects were detected when the same analyses were applied to the HOXB1 locus, but there was evidence of an interaction between HOXA1, HOXB1, and gender in susceptibility to ASDs. CONCLUSIONS: The results support a role for HOXA1 in susceptibility to autism, and add to the existing body of evidence implicating early brain stem injury in the etiology of ASDs.

Culture models of neurodegenerative disease.

In order to investigate how mutant SOD1 protein or environmental exogenous stressors lead to the death of motor neurons, we have established several in vitro model systems. We describe some features of the various models in order to demonstrate the advantages and shortcomings of each system.

GDNF is trophic for mouse motoneurons that express a mutant superoxide dismutase (SOD-1) gene.

BACKGROUND AND METHODS: An in vitro system of motoneurons was established from mice carrying a transgene for a human superoxide dismutase-1 (SOD-1) with a gly93ala mutation that has been linked to familial amyotrophic lateral sclerosis (FALS). These cultures were characterized and used to compare the effects of glial cell line-derived neurotrophic factor (GDNF) on motoneurons expressing the mutant gene with those on normal motoneurons. RESULTS: Recombinant human GDNF (100 ng/ml) significantly promoted the survival of a subpopulation of choline acetyltransferase (ChAT)-immunoreactive motoneurons that were also immunoreactive for the homeoprotein islet-1 in cultures from both wild type and mutant SOD-1 mice. However, GDNF did not increase the total number of ChAT-immunoreactive neurons in cultures from either wild type or transgenic mice. A distinct subpopulation of islet-1-immunoreactive motoneurons characterized by a soma 3 1/2 times larger and a ten-fold increase in neurite length was observed exclusively in GDNF-treated cultures. In cultures from mutant SOD-1 mice, there were 3 1/2 times as many motoneurons of this subpopulation as in wild type cultures at 6 days in vitro. In addition, this subpopulation of neurons survived for 10 days in vitro, the longest time point studied, in culture from mutant SOD-1 mice, but not in cultures from wild type mice. This subpopulation was also present at 6 days in vitro in cultures from mutant SOD-1 mice that received GDNF at 3 days in vitro instead of at the time of plating, suggesting that GDNF promotes the differentiation of these neurons. CONCLUSION: Our observations suggest that the expression of a mutant SOD-1 gene, as occurs in familial ALS, does not compromise the trophic effects of GDNF on motoneuron survival, but may affect the development of motoneurons.

Intramuscular grafts of myoblasts genetically modified to secrete glial cell line-derived neurotrophic factor prevent motoneuron loss and disease progression in a mouse model of familial amyotrophic lateral sclerosis.

Effects of ex vivo GDNF gene delivery on the degeneration of motoneurons were studied in the G1H transgenic mouse model of familial ALS carrying a human superoxide dismutase (SOD1) with a Gly93Ala mutation (Gurney et al., 1994). Retroviral vectors were made to produce human GDNF or E. coli beta-galactosidase (beta-Gal) by transient transfection of the Phoenix cell line and used to infect primary mouse myoblasts. In 6-week-old G1H mice, 50,000 myoblasts per muscle were injected bilaterally into two hindlimb muscles. Untreated G1H and wild-type mice served as additional controls. At 17 weeks of age, 1 week before sacrifice, these muscles were injected with fluorogold (FG) to retrogradely label spinal motoneurons that maintained axonal projections to the muscles. There were significantly more large FG-labeled alpha motoneurons at 18 weeks in GDNF-treated G1H mice than in untreated and beta-Gal-treated G1H mice. A morphometric study of motoneuron size distribution showed that GDNF shifted the size distribution of motoneurons toward larger cells compared with control G1H mice, although the average size and number of large motoneurons in GDNF-treated mice were less than that in wild-type mice. GDNF also prolonged the onset of disease, delayed the deterioration of performance in tests of motor behavior, and slowed muscle atrophy. Quantitative, real-time RT-PCR and PCR showed persistence of transgene mRNA and DNA in muscle for up to 12 weeks postgrafting. These observations demonstrate that ex vivo GDNF gene therapy in a mouse model of FALS promotes the survival of functional motoneurons, suggesting that a similar approach might delay the progression of neurodegeneration in ALS.

Cells from individuals with SOD-1 associated familial amyotrophic lateral sclerosis do not have an increased susceptibility to radiation-induced free radical production or DNA damage.

Oxidative stress may play a role in the pathogenesis of familial amyotrophic lateral sclerosis (FALS). Superoxide dismutases (SODs) are enzymes that can influence free radical processes in irradiated cells and there is some evidence that manipulation of SODs can affect survival of cells after radiation treatments. SOD-1 associated FALS mutants may have an altered radiation response due to an enhanced generation of hydroxyl radicals or a compromised ability to neutralize free radicals. We have investigated the ability of the lymphoblastoid cell lines from FALS patients with SOD-1 gene mutations, patients with sporadic ALS and controls to handle oxidative stress induced by ionising radiation by measuring levels of intracellular reactive oxygen species and production of DNA double-strand breaks. Levels of reactive oxygen species, expressed as the slope of the relative fluorescence of a radical-reactive fluorochrome, in the cells from familial ALS patients with SOD-1 gene mutations (2.14+/-1.06 Gy(-1)) and patients with sporadic ALS (1.38+/-0.21 Gy(-1)) were not significantly different from the controls (1.54+/-0.39 Gy(-1)). No significant difference was observed in the production of DNA double-strand breaks between three groups. The ability of lymphoblastoid cells from FALS patients with SOD-1 gene mutations to scavenge radiation-induced free radicals is not compromised nor is their ability to protect DNA damage induced by ionising radiation.

Definitive molecular diagnosis of facioscapulohumeral dystrophy.

OBJECTIVE: To establish the usefulness of a molecular diagnostic protocol for the autosomal dominant disease facioscapulohumeral dystrophy (FSHD). BACKGROUND: The genetic defect underlying the majority of cases is a deletion on chromosome 4q35 that is not associated with the coding sequence of any known gene. Molecular diagnosis of FSHD involves the visualization of this deletion as a "small" EcoRI restriction fragment. However, molecular diagnostics are complicated because of the homology of the telomeric regions of chromosomes 4q and 10q; the homologous 10q26 EcoRI fragments are also detected, and can fall into the size range considered to be diagnostic for FSHD. It is therefore important to distinguish the 4q35 and 10q26 EcoRI fragments, taking advantage of the presence of additional restriction sites (BlnI) in the alleles of chromosome 10q origin. METHODS: Paired digests of genomic DNA (EcoRI only and EcoRI/BlnI double digest), followed by pulsed field gel electrophoresis (PFGE), were used to establish the molecular diagnosis of FSHD in 82 unrelated index cases (46 familial, 24 proven sporadic with de novo mutations, and 12 with uncertain family history). RESULTS: In all cases fulfilling FSHD diagnostic criteria, a 4q35 EcoRI allele size of < or = 38 kb was present. The smallest 4q35 EcoRI allele in 205 normal control subjects was 41 kb. EcoRI alleles < or = 38 kb of chromosome 10q26 origin were present in 11.2% of this control group. In problematic cases, it was possible to resolve the diagnostic question. CONCLUSIONS: The combination of double digestion with EcoRI and BlnI followed by PFGE is the most reliable molecular protocol for distinguishing patients with FSHD.

Up-regulation of protein chaperones preserves viability of cells expressing toxic Cu/Zn-superoxide dismutase mutants associated with amyotrophic lateral sclerosis.

Mutations in the Cu/Zn-superoxide dismutase (SOD-1) gene underlie some familial cases of amyotrophic lateral sclerosis, a neurodegenerative disorder characterized by loss of cortical, brainstem, and spinal motor neurons. We present evidence that SOD-1 mutants alter the activity of molecular chaperones that aid in proper protein folding and targeting of abnormal proteins for degradation. In a cultured cell line (NIH 3T3), resistance to mutant SOD-1 toxicity correlated with increased overall chaperoning activity (measured by the ability of cytosolic extracts to prevent heat denaturation of catalase) as well as with up-regulation of individual chaperones/stress proteins. In transgenic mice expressing human SOD-1 with the G93A mutation, chaperoning activity was decreased in lumbar spinal cord but increased or unchanged in clinically unaffected tissues. Increasing the level of the stress-inducible chaperone 70-kDa heat shock protein by gene transfer reduced formation of mutant SOD-containing proteinaceous aggregates in cultured primary motor neurons expressing G93A SOD-1 and prolonged their survival. We propose that insufficiency of molecular chaperones may be directly involved in loss of motor neurons in this disease.

Glutamate potentiates the toxicity of mutant Cu/Zn-superoxide dismutase in motor neurons by postsynaptic calcium-dependent mechanisms.

Mutations in the Cu/Zn-superoxide dismutase (SOD-1) gene are responsible for a subset of familial cases of amyotrophic lateral sclerosis. Using a primary culture model, we have demonstrated that normally nontoxic glutamatergic input, particularly via calcium-permeable AMPA/kainate receptors, is a major factor in the vulnerability of motor neurons to the toxicity of SOD-1 mutants. Wild-type and mutant (G41R, G93A, or N139K) human SOD-1 were expressed in motor neurons of dissociated cultures of murine spinal cord by intranuclear microinjection of plasmid expression vector. Both a general antagonist of AMPA/kainate receptors (CNQX) and a specific antagonist of calcium-permeable AMPA receptors (joro spider toxin) reduced formation of SOD-1 proteinaceous aggregates and prevented death of motor neurons expressing SOD-1 mutants. Partial protection was obtained by treatment with nifedipine, implicating Ca2+ entry through voltage-gated calcium channels as well as glutamate receptors in potentiating the toxicity of mutant SOD-1 in motor neurons. Dramatic neuroprotection was obtained by coexpressing the calcium-binding protein calbindin-D28k but not by increasing intracellular glutathione levels or treatment with the free radical spin trap agent, N-tert-butyl-alpha-phenylnitrone. Thus, generalized oxidative stress could have contributed in only a minor way to death of motor neurons expressing the mutant SOD-1. These studies demonstrated that the toxicity of these mutants is calcium-dependent and provide direct evidence that calcium entry during neurotransmission, coupled with deficiency of cytosolic calcium-binding proteins, is a major factor in the preferential vulnerability of motor neurons to disease.

Selective loss of alpha motoneurons innervating the medial gastrocnemius muscle in a mouse model of amyotrophic lateral sclerosis.

Mutations in the superoxide dismutase gene 1 (SOD-1) are found in patients with familial amyotrophic lateral sclerosis (FALS). Overexpression of a mutated human SOD-1 gene in mice results in neurodegenerative disease as result of motoneuron loss in lumbar spinal cord (10). Using this mouse model of FALS, we have established a quantitative assay utilizing the retrograde tracer Fluorogold (FG) to determine the number of motoneurons innervating one skeletal muscle in mice with ongoing disease. In adult wild-type mice, the number of alpha motoneurons retrogradely labeled by an injection of FG into medial gastrocnemius muscle is 50 +/- 7 and this number remains constant from 7 to 18 weeks of age. In mutant mice, the number of alpha motoneurons retrogradely labeled by FG is the same as in wild-type mice at 7 and 9 weeks, but then declines to 36% of that in normal mice at 18 weeks. This decline also correlates positively to severity of motor impairments in these mice as assessed by the hindlimb splay test. In contrast, the number of FG-labeled gamma motoneurons remains relatively unchanged in both wild-type and mutant mice up to 18 weeks. At 18 weeks of age, this apparent alpha motoneuron denervation is paralleled by an average of 55% reduction of MG-muscle mass and 40% weaker performance in the hindlimb splay test. These data suggest that alpha motoneurons are the most vulnerable neuronal subtype in this mouse model of ALS and it is primarily their loss that leads to functional motor deficits. This quantitative bioassay also will be valuable for evaluating novel therapeutics for ALS.