Degenerative myelopathy associated with a missense mutation in the superoxide dismutase 1 (SOD1) gene progresses to peripheral neuropathy in Pembroke Welsh Corgis and Boxers

Genotypic and Allelic Frequencies of Degenerative Myelopathy in an Italian Canine Population

Canine degenerative myelopathy is a fatal neurodegenerative disorder that affects the spinal cord. It is a late-onset disease, with symptoms becoming evident later in life at approximately 8 years of age. The principal aim of this study was to retrospectively evaluate allelic and genotypic frequencies of the c.118G > A and c.52A > T mutations located on the SOD1 gene in an Italian canine population to provide detailed information on the prevalence of the mutations in the country. The genetic data of different breeds were collected through DNA tests over a nine-year period in the Italian canine population. For each dog, the breed, sex, age, and DNA test results were recorded. Allelic and genotypic frequencies were calculated. A total of 1667 DNA tests for the c.118G > A and c.52A > T mutations were carried out on 84 breeds. For the analysis of prevalence, only breeds counting more than 20 subjects have been considered, for a total of 1410 DNA tests obtained from 13 different breeds. In the population tested for the c.118G > A mutation, 65.47% (n. 893) of the subjects were clear, 25.59% (n. 349) were heterozygous carriers, and 8.94% (n. 122) were homozygous for the mutated allele. The mutation showed the highest frequency in Pembroke Welsh Corgis (55.49%) and the lowest frequencies in Poodles (6.32%) and Australian Shepherds (7.14%). The allelic frequency of the c.52A > T mutation was 7.61% in the Bernese Mountain dog. Neither variant differed between females and males in genotypic frequencies. The present study provides insights into the allelic and genotypic frequencies of canine degenerative myelopathy in different dog breeds in Italy.

Electrodiagnostic testing in dogs with disorders of the spinal cord or cauda equina

Electrodiagnostic (EDX) testing is uncommonly utilized in dogs other than for investigation of disorders of the neuromuscular system. In dogs with diseases affecting the spinal cord or cauda equina, EDX testing can provide functional data complementary to imaging information that together can guide therapeutic and management approaches. Additionally, in some clinical scenarios, EDX testing prior to advanced imaging is integral to identifying if there is spinal cord or cauda equina involvement and can aid in determining the appropriate diagnostic path. This review will outline EDX testing methods that have been reported in dogs relating to the diagnosis, monitoring or prognosis of various conditions affecting the spinal cord and cauda equina. The various tests will be briefly outlined regarding how they are performed and what information is provided. The main focus will be on clinical applications including highlighting situations where EDX testing is useful for differentiating between neurologic and non-neurologic presentations. Additional ways these EDX techniques could be incorporated in the management of diseases of the spinal cord and cauda equina in dogs will be presented.

An Overview of Canine Inherited Neurological Disorders with Known Causal Variants

Hereditary neurological conditions documented in dogs encompass congenital, neonatal, and late-onset disorders, along with both progressive and non-progressive forms. In order to identify the causal variant of a disease, the main two approaches are genome-wide investigations and candidate gene investigation. Online Mendelian Inheritance in Animals currently lists 418 Mendelian disorders specific to dogs, of which 355 have their likely causal genetic variant identified. This review aims to summarize the current knowledge on the canine nervous system phenes and their genetic causal variant. It has been noted that the majority of these diseases have an autosomal recessive pattern of inheritance. Additionally, the dog breeds that are more prone to develop such diseases are the Golden Retriever, in which six inherited neurological disorders with a known causal variant have been documented, and the Belgian Shepherd, in which five such disorders have been documented. DNA tests can play a vital role in effectively managing and ultimately eradicating inherited diseases.

A SACS deletion variant in Great Pyrenees dogs causes autosomal recessive neuronal degeneration

ARSACS (autosomal recessive spastic ataxia of Charlevoix-Saguenay) is a human neurological disorder characterized by progressive cerebellar ataxia and peripheral neuropathy. A recently recognized disorder in Great Pyrenees dogs is similarly characterized by widespread central nervous system degeneration leading to progressive cerebellar ataxia and spasticity, combined with peripheral neuropathy. Onset of clinical signs occurred in puppies as young as 4 months of age, with slow progression over several years. A multi-generation pedigree suggested an autosomal recessive mode of inheritance. Histopathology revealed consistent cerebellar Purkinje cell degeneration, neuronal degeneration in brainstem nuclei, widespread spinal cord white matter degeneration, ganglion cell degeneration, inappropriately thin myelin sheaths or fully demyelinated peripheral nerve fibers, and normal or only mild patterns of denervation atrophy in skeletal muscles. Genome-wide single nucleotide polymorphism (SNP) genotype data was collected from 6 cases and 26 controls, where homozygosity mapping identified a 3.3 Mb region on CFA25 in which all cases were homozygous and all controls were either heterozygous or homozygous for alternate haplotypes. This region tagged the SACS gene where variants are known to cause ARSACS. Sanger sequencing of SACS in affected dogs identified a 4 bp deletion that causes a frame shift and truncates 343 amino acids from the C terminus of the encoded sacsin protein (p.Val4244AlafsTer32). Our clinical and histopathological descriptions of this canine disorder contribute to the description of human ARSACS and represents the first naturally occurring large animal model of this disorder.

Intensive neurorehabilitation and allogeneic stem cells transplantation in canine degenerative myelopathy

Introduction

Degenerative myelopathy (DM) is a neurodegenerative spinal cord disease with upper motor neurons, with progressive and chronic clinical signs, similar to amyotrophic lateral sclerosis (ALS). DM has a complex etiology mainly associated with SOD1 gene mutation and its toxic role, with no specific treatment. Daily intensive rehabilitation showed survival time near 8 months but most animals are euthanized 6-12 months after clinical signs onset.

Methods

This prospective controlled blinded cohort clinical study aims to evaluate the neural regeneration response ability of DM dogs subjected to an intensive neurorehabilitation protocol with mesenchymal stem cells (MSCs) transplantation. In total, 13 non-ambulatory (OFS 6 or 8) dogs with homozygous genotype DM/DM and diagnosed by exclusion were included. All were allocated to the intensive neurorehabilitation with MSCs protocol (INSCP) group (n = 8) or to the ambulatory rehabilitation protocol (ARP) group (n = 5), which differ in regard to training intensity, modalities frequency, and MSCs transplantation. The INSCP group was hospitalized for 1 month (T0 to T1), followed by MSCs transplantation (T1) and a second month (T2), whereas the ARP group was under ambulatory treatment for the same 2 months.

Results

Survival mean time of total population was 375 days, with 438 days for the INSCP group and 274 for the ARP group, with a marked difference on the Kaplan-Meier survival analysis. When comparing the literature's results, there was also a clear difference in the one-sample t-test (p = 0.013) with an increase in time of approximately 70%. OFS classifications between groups at each time point were significantly different (p = 0.008) by the one-way ANOVA and the independent sample t-test.

Discussion

This INSCP showed to be safe, feasible, and a possibility for a long progression of DM dogs with quality of life and functional improvement. This study should be continued.

Electrical Impedance Myography in Dogs With Degenerative Myelopathy

Canine degenerative myelopathy (DM) leads to disuse and neurogenic muscle atrophy. Currently there is a lack of non-invasive quantitative measures of muscle health in dogs with DM. Muscle pathology has been previously quantified in other disorders using the technique of electrical impedance myography (EIM) but it has not been reported for DM. The objective of this study was to compare EIM between DM-affected and similar aged healthy dogs as well as assess EIM changes over time in DM-affected dogs. Multifrequency EIM was performed on DM affected dogs at baseline and during disease progression and on age-matched healthy dogs. Muscles evaluated in the pelvic limbs included the craniotibialis, gastrocnemius, gracilis, sartorius, and biceps femoris. The 100 kHz phase angle was extracted from the full frequency set for analysis. Phase values were lower in DM dogs as compared to healthy controls. Specifically, phase of the gastrocnemius was lower on the left (θ = 7.69, 13.06; p =0.002) and right (θ= 6.11, 11.72; p = 0.001) in DM vs. control dogs, respectively. The mean phase value of all measured muscles was also lower on the left (θ = 9.24, 11.62; p = 0.012) and right (θ = 9.18, 11.72; p = 0.021). Other individual muscles measured did not reach statistical significance, although values were consistently lower in DM-affected dogs. With disease progression, downward trends in phase values were detected in DM-affected dogs when monitored serially over time. This study demonstrates that EIM 100 kHz phase values are sensitive to muscle pathology in DM and that phase values are decreased in dogs with DM. Measurements from the gastrocnemius muscle show the greatest differences from similar aged healthy dogs suggesting it may be the preferred muscle for future EIM studies.

Description of breed ancestry and genetic health traits in arctic sled dog breeds

Background

This study describes the presence and frequency of health traits among three populations of dogs traditionally used for sledding and explores their ancestry and breed composition as provided by the commercially available Embark dog DNA test. The three populations include the purebred Siberian Husky and the admixed populations of Alaskan sled dogs and Polar Huskies. While the Siberian Husky represents a well-established breed with extensive historical and health data, the Alaskan sled dog is less studied but has been the subject of nutritional, physiological, and genetic studies related to ancestry and performance. In contrast, the Polar Husky is a relatively obscure and rare group of dogs used for arctic exploration with very little-known information. The three populations were compared using Embark results, providing new insight into the health traits circulating within the populations and the potential ancestral linkage of the health traits between the sledding populations. Embark results are based upon 228,588 single-nucleotide polymorphisms (SNPs) spanning the canine genome, characterized using a custom-designed Illumina beadchip array.

Results

Specifically, breed composition was summarized for the two admixed populations with most of the dogs being predominantly categorized as Alaskan husky- type dog or “Supermutt”. Mitochondrial and Y chromosome haplogroups and haplotypes were found with Alaskan sled dogs carrying most of the haplogroups and types found in Siberian and Polar Huskies. Genomic principal component analysis reflected population structure corresponding to breed and substructure within the Alaskan sled dogs related to sprint or distance competition. Genetic markers associated with Alanine Aminotransferase activity, Alaskan Husky Encephalopathy, dilated cardiomyopathy, Collie eye anomaly, degenerative myelopathy, ichthyosis, and factor VII deficiency were identified in the populations of sledding breeds.

Conclusion

These results provide a preliminary description of genetic characteristics found in sledding breeds, improving the understanding and care of working sled dogs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40575-021-00108-z.

Allele and genotype frequencies of the SOD1 gene polymorphism associated with canine degenerative myelopathy in Belgian Malinois dogs in Greece

Background and Aim

Canine degenerative myelopathy (CDM) is an adult-onset fatal disorder associated with a point mutation of the superoxide dismutase 1 (SOD1) gene (SOD1:c.118G>A). This study aimed to determine the allele and genotype frequencies of this mutation in a group of Belgian Malinois dogs in Greece.

Materials and Methods

Samples (n=72) of whole blood were collected from 72 purebred dogs of the Hellenic Armed Forces; these samples were processed for DNA isolation, polymerase chain reaction, and digestion with the restriction endonuclease AcuI. Sample testing was conducted in compliance with ISO17025 accreditation requirements.

Results

The observed relative genotype frequencies were 71% for the homozygous (GG), 25% for the heterozygous (AG), and 4% for the homozygous mutant (AA) alleles. These frequencies were close to those expected, indicating no significant departure from Hardy-Weinberg equilibrium (HWE, p=0.395). The frequency of heterozygous animals indicates that a high risk of developing CDM in forthcoming generations exists in the tested population because mating among carriers would result in 25% AA progeny. The medical record of the group of study animals indicated selection against leishmaniosis, as applied throughout generations by owners and breeders. The potential association of this selection with the HWE status of the study population was discussed.

Conclusion

The SOD1:c.118G>A mutation was common in the tested group of dogs; thus, they are suitable for a follow-up investigation on the development and progression of CDM. A case-control study on animals with evidence of sensitivity to infectious myelopathy could provide new insights into disease pathogenesis.

In vitro evidence consistent with an interaction between wild-type and mutant SOD1 protein associated with canine degenerative myelopathy

Canine degenerative myelopathy (DM) is a progressive neurological disorder that may be considered to be a large animal model for specific forms of the fatal human disease, familial amyotrophic lateral sclerosis (fALS). DM is associated with a c118G>A mutation of the superoxide dismutase 1 (Sod1) gene, and a significant proportion of cases are inherited in an autosomal recessive manner in contrast to the largely, but not exclusively, dominant mode of inheritance in fALS. The consensus view is that these Sod1/SOD1 mutations result in a toxic gain of function but the mechanisms remain unclear. Here we used an in vitro neuroblastoma cell line transfection system to monitor wild-type and mutant forms of SOD1 fusion proteins containing either a Cherry or an enhanced green fluorescent protein (EGFP) tag. These fusion proteins retained SOD1 enzymatic activity on a native gel assay system. We demonstrate that SOD1 aggregate density is significantly higher in DM transfectants compared to wild-type. In addition, we show by co-immunoprecipitation and confocal microscopy, evidence for a potential interaction between wild-type and mutant forms of SOD1 in co-transfected cells. While in vitro studies have shown SOD1 heterodimer formation in fALS models, this is the first report for DM SOD1. Therefore, despite for the majority of cases there is a difference in the mode of inheritance between fALS and DM, a similar interaction between wild-type and mutant SOD1 forms can occur. Clarifying the role of SOD1 in DM may also be of benefit to understanding the role of SOD1 in fALS.

Arginase-1 expressing microglia in close proximity to motor neurons were increased early in disease progression in canine degenerative myelopathy, a model of amyotrophic lateral sclerosis

Toxicity within superoxide dismutase-1 (SOD1)-associated familial amyotrophic lateral sclerosis (ALS) is non-cell autonomous with direct contribution from microglia. Microglia exhibit variable expression of neuroprotective and neurotoxic molecules throughout disease progression. The mechanisms regulating microglial phenotype within ALS are not well understood. This work presents a first study to examine the specific microglial phenotypic response in close association to motor neurons in a naturally occurring disease model of ALS, canine degenerative myelopathy (DM). Microglia closely associated with motor neurons were increased in all stages of DM progression, although only DM Late reached statistical significance. Furthermore, the number of arginase-1 expressing microglia per motor neuron were significantly increased in early stages of DM, whereas the number of inducible nitric oxide synthase (iNOS)-expressing microglia per motor neuron was indistinguishable from aged controls at all stages of disease. Fractalkine, a chemotactic molecule for microglia, was expressed in motor neurons, and the fractalkine receptor was specifically localized to microglia. However, we found no correlation between microglial response and lumbar spinal cord fractalkine levels. Taken together, these data suggest that arginase-1-expressing microglia are recruited to the motor neuron early in DM disease through a fractalkine-independent mechanism.

Immunohistochemical analysis of canine and feline muscle disorders using formalin-fixed, paraffin-embedded tissues

Histochemical techniques used in examination of muscle biopsies typically require frozen sections. Given that most of the specimens submitted to a veterinary laboratory for diagnosis are formalin-fixed, the choice of staining methods is limited. We aimed to further advance the diagnostic capabilities of pathologists presented with formalin-fixed muscle samples and to describe the differences in immunohistopathologic findings between neurogenic and myogenic muscle disorders. Based on hematoxylin and eosin staining, we defined in dogs the histologic lesions in 4 neurogenic disorders (degenerative myelopathy and polyneuropathy) and 2 myogenic disorders (dystrophin-deficient muscular dystrophy). In cats, we defined the lesions in 2 neurogenic disorders (lymphoma of nerve roots and spinal cords) and 1 myogenic disorder (laminin α2-deficient muscular dystrophy). Immunohistochemistry for slow and fast myosins revealed angular and group atrophy of type 1 and type 2 fibers in dogs and cats, and fiber type grouping in dogs. These immunohistopathologic findings were specific to neurogenic muscle disorders. Immunohistochemistry for nestin and myogenin revealed nestin-positive fibers and myogenin-positive nuclei in dogs and cats. They were not specific, but these fibers in myogenic disorders can be interpreted as regenerating fibers. The immunohistochemical method described herein appears to be useful for discriminating neurogenic and myogenic disorders in formalin-fixed, paraffin-embedded muscle tissue of dogs and cats.

Cerebrospinal Fluid Levels of Phosphorylated Neurofilament Heavy as a Diagnostic Marker of Canine Degenerative Myelopathy

BACKGROUND

No definitive, antemortem diagnostic test for canine degenerative myelopathy (DM) is available. Phosphorylated neurofilament heavy (pNF-H) is a promising biomarker for nervous system diseases.

HYPOTHESIS/OBJECTIVE

Cerebrospinal fluid (CSF) and serum pNF-H is a detectable biological marker for diagnosis of canine DM.

ANIMALS

Fifty-three DM-affected, 27 neurologically normal, 7 asymptomatic at-risk, and 12 DM mimic dogs.

METHODS

Archived CSF and serum pNF-H concentrations were determined by a commercially available ELISA. A receiver-operating characteristic (ROC) curve was generated with CSF values.

RESULTS

Compared with old control dogs, median CSF pNF-H concentration was increased in all stages of DM; old dogs 5.1 ng/mL (interquartile range [IQR] 1.4-9.3) versus DM stage 1 23.9 ng/mL (IQR 20.8-29.6; P < .05) versus DM stage 2 36.8 ng/mL (IQR 22.9-51.2; P < .0001) versus DM stage 3 25.2 ng/mL (IQR 20.2-61.8; P < .001) versus DM stage 4 38.0 ng/mL (IQR 11.6-59.9; P < .01). Degenerative myelopathy stage 1 dogs had increased median CSF pNF-H concentrations compared with asymptomatic, at-risk dogs (3.4 ng/mL [IQR 1.5-10.9; P < .01]) and DM mimics (6.6 ng/mL [IQR 3.0-12.3; P < .01]). CSF pNF-H concentration >20.25 ng/mL was 80.4% sensitive (confidence interval [CI] 66.09-90.64%) and 93.6% specific (CI 78.58-99.21%) for DM. Area under the ROC curve was 0.9467 (CI 0.92-0.9974). No differences in serum pNF-H concentration were found between control and DM-affected dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

pNF-H concentration in CSF is a sensitive biomarker for diagnosis of DM. Although there was high specificity for DM in this cohort, further study should focus on a larger cohort of DM mimics, particularly other central and peripheral axonopathies.

Resolution of polyneuropathy in a hypothyroid dog following thyroid supplementation

An 8 yr old male golden retriever was evaluated because of chronic, progressive, multiple neurologic signs. Physical examination showed marked obesity and facial swelling with a "tragic facial expression." Neurologic evaluation revealed the dog had multiple cranial nerve deficits and lower motor neuron signs in the pelvic limbs. Serum biochemical analysis and thyroid function tests were consistent with hypothyroidism. A biopsy from the common peroneal nerve revealed a loss of myelinated fibers, inappropriately thin myelinated fibers, and resolving subperineurial edema. The diagnosis of polyneuropathy associated with hypothyroidism was made. Levothyroxine therapy was initiated. Response to levothyroxine treatment was slow, with most neurologic abnormalities persisting for >6 wk. However, the dog made a full neurologic recovery within 6 mo. Although the occurrence of polyneuropathy in dogs resulting from hypothyroidism has been controversial, the study authors demonstrated that hypothyroid polyneuropathy can occur in dogs as documented in humans. This is the first report describing long-term follow-up information together with detailed pathological features of hypothyroid polyneuropathy in a dog. In hypothyroid polyneuropathy, the response to thyroid replacement may be slow, but a recovery can be expected if treatment is initiated before peripheral nerve fiber loss becomes severe.

Variants within the SP110 nuclear body protein modify risk of canine degenerative myelopathy

Canine degenerative myelopathy (DM) is a naturally occurring neurodegenerative disease with similarities to some forms of amyotrophic lateral sclerosis (ALS). Most dogs that develop DM are homozygous for a common superoxide dismutase 1 gene (SOD1) mutation. However, not all dogs homozygous for this mutation develop disease. We performed a genome-wide association analysis in the Pembroke Welsh Corgi (PWC) breed comparing DM-affected and -unaffected dogs homozygous for the SOD1 mutation. The analysis revealed a modifier locus on canine chromosome 25. A haplotype within the SP110 nuclear body protein (SP110) was present in 40% of affected compared with 4% of unaffected dogs (P = 1.5 × 10(-5)), and was associated with increased probability of developing DM (P = 4.8 × 10(-6)) and earlier onset of disease (P = 1.7 × 10(-5)). SP110 is a nuclear body protein involved in the regulation of gene transcription. Our findings suggest that variations in SP110-mediated gene transcription may underlie, at least in part, the variability in risk for developing DM among PWCs that are homozygous for the disease-related SOD1 mutation. Further studies are warranted to clarify the effect of this modifier across dog breeds.

Changes in respiratory function in Pembroke Welsh Corgi dogs with degenerative myelopathy

Canine degenerative myelopathy (DM) is characterized by progressive degeneration of the spinal cord. Although atrophic changes in the intercostal muscles were previously reported in the late stage of DM in Pembroke Welsh Corgis (PWCs), changes in respiratory function have not yet been examined. In the present study, we performed an arterial blood gas analysis and measured respiratory movements over progressive disease stages to document changes in respiratory function in DM-affected PWCs. We found that respiratory dysfunction progressed during the later stages of DM and correlated with a change in respiratory movement to the abdominal breathing pattern. These results suggested that hypoventilation occurred due to dysfunctional changes in the intercostal muscles and resulted in hypoxemia in the later stages of DM.

Aggregation propensities of superoxide dismutase G93 hotspot mutants mirror ALS clinical phenotypes

Protein framework alterations in heritable Cu, Zn superoxide dismutase (SOD) mutants cause misassembly and aggregation in cells affected by the motor neuron disease ALS. However, the mechanistic relationship between superoxide dismutase 1 (SOD1) mutations and human disease is controversial, with many hypotheses postulated for the propensity of specific SOD mutants to cause ALS. Here, we experimentally identify distinguishing attributes of ALS mutant SOD proteins that correlate with clinical severity by applying solution biophysical techniques to six ALS mutants at human SOD hotspot glycine 93. A small-angle X-ray scattering (SAXS) assay and other structural methods assessed aggregation propensity by defining the size and shape of fibrillar SOD aggregates after mild biochemical perturbations. Inductively coupled plasma MS quantified metal ion binding stoichiometry, and pulsed dipolar ESR spectroscopy evaluated the Cu(2+) binding site and defined cross-dimer copper-copper distance distributions. Importantly, we find that copper deficiency in these mutants promotes aggregation in a manner strikingly consistent with their clinical severities. G93 mutants seem to properly incorporate metal ions under physiological conditions when assisted by the copper chaperone but release copper under destabilizing conditions more readily than the WT enzyme. Altered intradimer flexibility in ALS mutants may cause differential metal retention and promote distinct aggregation trends observed for mutant proteins in vitro and in ALS patients. Combined biophysical and structural results test and link copper retention to the framework destabilization hypothesis as a unifying general mechanism for both SOD aggregation and ALS disease progression, with implications for disease severity and therapeutic intervention strategies.

The chaperone protein clusterin may serve as a cerebrospinal fluid biomarker for chronic spinal cord disorders in the dog

Chronic spinal cord dysfunction occurs in dogs as a consequence of diverse aetiologies, including long-standing spinal cord compression and insidious neurodegenerative conditions. One such neurodegenerative condition is canine degenerative myelopathy (DM), which clinically is a challenge to differentiate from other chronic spinal cord conditions. Although the clinical diagnosis of DM can be strengthened by the identification of the Sod1 mutations that are observed in affected dogs, genetic analysis alone is insufficient to provide a definitive diagnosis. There is a requirement to identify biomarkers that can differentiate conditions with a similar clinical presentation, thus facilitating patient diagnostic and management strategies. A comparison of the cerebrospinal fluid (CSF) protein gel electrophoresis profile between idiopathic epilepsy (IE) and DM identified a protein band that was more prominent in DM. This band was subsequently found to contain a multifunctional protein clusterin (apolipoprotein J) that is protective against endoplasmic reticulum (ER) stress-mediated apoptosis, oxidative stress, and also serves as an extracellular chaperone influencing protein aggregation. Western blot analysis of CSF clusterin confirmed elevated levels in DM compared to IE (p < 0.05). Analysis of spinal cord tissue from DM and control material found that clusterin expression was evident in neurons and that the clusterin mRNA levels from tissue extracts were elevated in DM compared to the control. The plasma clusterin levels was comparable between these groups. However, a comparison of clusterin CSF levels in a number of neurological conditions found that clusterin was elevated in both DM and chronic intervertebral disc disease (cIVDD) but not in meningoencephalitis and IE. These findings indicate that clusterin may potentially serve as a marker for chronic spinal cord disease in the dog; however, additional markers are required to differentiate DM from a concurrent condition such as cIVDD.

Breed distribution of SOD1 alleles previously associated with canine degenerative myelopathy

Background

Previous reports associated 2 mutant SOD1 alleles (SOD1:c.118A and SOD1:c.52T) with degenerative myelopathy in 6 canine breeds. The distribution of these alleles in other breeds has not been reported.

Objective

To describe the distribution of SOD1:c.118A and SOD1:c.52T in 222 breeds.

Animals

DNA from 33,747 dogs was genotyped at SOD1:c.118,SOD1:c.52, or both. Spinal cord sections from 249 of these dogs were examined.

Methods

Retrospective analysis of 35,359 previously determined genotypes at SOD1:c.118G>A or SOD1:c.52A>T and prospective survey to update the clinical status of a subset of dogs from which samples were obtained with a relatively low ascertainment bias.

Results

The SOD1:c.118A allele was found in cross‐bred dogs and in 124 different canine breeds whereas the SOD1:c.52T allele was only found in Bernese Mountain Dogs. Most of the dogs with histopathologically confirmed degenerative myelopathy were SOD1:c.118A homozygotes, but 8 dogs with histopathologically confirmed degenerative myelopathy were SOD1:c.118A/G heterozygotes and had no other sequence variants in their SOD1 amino acid coding regions. The updated clinical conditions of dogs from which samples were obtained with a relatively low ascertainment bias suggest that SOD1:c.118A homozygotes are at a much higher risk of developing degenerative myelopathy than are SOD1:c.118A/G heterozygotes.

Conclusions and Clinical Importance

We conclude that the SOD1:c.118A allele is widespread and common among privately owned dogs whereas the SOD1:c.52T allele is rare and appears to be limited to Bernese Mountain Dogs. We also conclude that breeding to avoid the production of SOD1:c.118A homozygotes is a rational strategy.

Characterization of thoracic motor and sensory neurons and spinal nerve roots in canine degenerative myelopathy, a potential disease model of amyotrophic lateral sclerosis

Canine degenerative myelopathy (DM) is a progressive, adult-onset, multisystem degenerative disease with many features in common with amyotrophic lateral sclerosis (ALS). As with some forms of ALS, DM is associated with mutations in superoxide dismutase 1 (SOD1). Clinical signs include general proprioceptive ataxia and spastic upper motor neuron paresis in pelvic limbs, which progress to flaccid tetraplegia and dysphagia. The purpose of this study was to characterize DM as a potential disease model for ALS. We previously reported that intercostal muscle atrophy develops in dogs with advanced-stage DM. To determine whether other components of the thoracic motor unit (MU) also demonstrated morphological changes consistent with dysfunction, histopathologic and morphometric analyses were conducted on thoracic spinal motor neurons (MNs) and dorsal root ganglia (DRG) and in motor and sensory nerve root axons from DM-affected boxers and Pembroke Welsh corgis (PWCs). No alterations in MNs or motor root axons were observed in either breed. However, advanced-stage PWCs exhibited significant losses of sensory root axons, and numerous DRG sensory neurons displayed evidence of degeneration. These results indicate that intercostal muscle atrophy in DM is not preceded by physical loss of the motor neurons innervating these muscles, nor of their axons. Axonal loss in thoracic sensory roots and sensory neuron death suggest that sensory involvement may play an important role in DM disease progression. Further analysis of the mechanisms responsible for these morphological findings would aid in the development of therapeutic intervention for DM and some forms of ALS.

Genetic testing of canine degenerative myelopathy in the South African Boxer dog population

Canine degenerative myelopathy (DM) is a progressive disease process that is diagnosed late in life and mainly affects the pelvic limbs. Factors that make an ante-mortem definitive diagnosis of DM include: an insidious onset and clinical manifestation that mimics other disease processes of the pelvic limbs (hip dysplasia, cranial cruciate ligament rupture, etc.) or there may even be concurrent disease processes, old-age onset and lack of reliable diagnostic methods. Until recently, South African dog owners had to submit samples to laboratories overseas for genetic testing in order to confirm an affected dog (homozygous A/A) and to aid in the ante-mortem diagnosis of DM. Only affected dogs have been confirmed to manifest the clinical signs of DM. This study aimed to verify whether genetic testing by a local genetic laboratory was possible in order to detect a missense mutation of the superoxide dismutase gene (SOD1) that is implicated in causing the clinical signs of DM. The study also aimed to detect and map the inheritance of this disease process in a local Boxer dog population where the pedigree of the sampled population was known. Venous blood collected from Boxer dogs using a simple random sampling technique. The samples were genotyped for the SOD1:c.118GA polymorphism. Carrier and affected Boxer dogs were detected. A pedigree that demonstrated the significance of inheriting a carrier or affected state in the population was mapped. The present study concludes that genotyping of the missense mutation in Boxer dogs is possible in South Africa. There are carrier and affected Boxer dogs in the local population, making DM a plausible diagnosis in aged dogs presenting with pelvic limb pathology.

Characterization of intercostal muscle pathology in canine degenerative myelopathy: a disease model for amyotrophic lateral sclerosis

Dogs homozygous for missense mutations in the SOD1 gene develop a late-onset neuromuscular disorder called degenerative myelopathy (DM) that has many similarities to amyotrophic lateral sclerosis (ALS). Both disorders are characterized by widespread progressive declines in motor functions, accompanied by atrophic changes in the descending spinal cord tracts. Some forms of ALS are also associated with SOD1 mutations. In end-stage ALS, death usually occurs as a result of respiratory failure from severe functional impairment of respiratory muscles. The mechanisms that lead to this loss of function are not known. Dogs with DM are euthanized at all stages of disease progression, providing an opportunity to characterize the onset and progression of any pathological changes in the respiratory muscles that may precede respiratory failure. To characterize such potential disease-related pathology, we evaluated intercostal muscles from Boxer and Pembroke Welsh Corgi dogs that were euthanized at various stages of DM disease progression. DM was found to result in intercostal muscle atrophy, fibrosis, increased variability in muscle fiber size and shape, and alteration in muscle fiber type composition. This pathology was not accompanied by retraction of the motor neuron terminals from the muscle acetylcholine receptor complexes, suggesting that the muscle atrophy did not result from physical denervation. These findings provide a better understanding of the mechanisms that likely lead to respiratory failure in at least some forms of ALS and will be useful in the development and evaluation of potential therapeutic interventions using the DM model.

Neuronal Loss and Decreased GLT-1 Expression Observed in the Spinal Cord of Pembroke Welsh Corgi Dogs With Canine Degenerative Myelopathy

Canine degenerative myelopathy (DM) is a progressive neurodegenerative disease that is frequently found in Pembroke Welsh Corgi (PWC) dogs. Canine DM is potentially a spontaneous animal model for human amyotrophic lateral sclerosis (ALS) because of similar lesions and the involvement of superoxide dismutase 1 (SOD1) mutation. However, the ventral horn lesion in DM has not been characterized in detail. Glutamate excitotoxicity due to deficiency of the glutamine-glutamate cycle has been implicated in neuron death in ALS. Thus, we examined 5 PWC dogs with an SOD1 mutation that were affected by DM, 5 non-DM PWC dogs, and 5 Beagle dogs without neurologic signs to assess the neuronal changes and the expression levels of 2 glial excitatory amino acid transporters (glutamate transporter 1 [GLT-1] and glutamate/aspartate transporter [GLAST]). The number of neurons in the spinal ventral horns of the DM dogs was significantly decreased, whereas no change was found in the cell size. Chromatolysis, lipofuscin-laden neurons, and marked synapse loss were also observed. GLT-1 expression was strikingly decreased in DM dogs, whereas GLAST expression showed no significant change. The results indicate that excitotoxicity related to the reduced expression of GLT-1, but not GLAST, may be involved in neuron loss in DM, as in human ALS, whereas intraneuronal events may differ between the 2 diseases.

Canine degenerative myelopathy: biochemical characterization of superoxide dismutase 1 in the first naturally occurring non-human amyotrophic lateral sclerosis model

Mutations in canine superoxide dismutase 1 (SOD1) have recently been shown to cause canine degenerative myelopathy, a disabling neurodegenerative disorder affecting specific breeds of dogs characterized by progressive motor neuron loss and paralysis until death, or more common, euthanasia. This discovery makes canine degenerative myelopathy the first and only naturally occurring non-human model of amyotrophic lateral sclerosis (ALS), closely paralleling the clinical, pathological, and genetic presentation of its human counterpart, SOD1-mediated familial ALS. To further understand the biochemical role that canine SOD1 plays in this disease and how it may be similar to human SOD1, we characterized the only two SOD1 mutations described in affected dogs to date, E40K and T18S. We show that a detergent-insoluble species of mutant SOD1 is present in spinal cords of affected dogs that increases with disease progression. Our in vitro results indicate that both canine SOD1 mutants form enzymatically active dimers, arguing against a loss of function in affected homozygous animals. Further studies show that these mutants, like most human SOD1 mutants, have an increased propensity to form aggregates in cell culture, with 10-20% of cells possessing visible aggregates. Creation of the E40K mutation in human SOD1 recapitulates the normal enzymatic activity but not the aggregation propensity seen with the canine mutant. Our findings lend strong biochemical support to the toxic role of SOD1 in canine degenerative myelopathy and establish close parallels for the role mutant SOD1 plays in both canine and human disorders.