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.

Upregulation of CB2 receptors in reactive astrocytes in canine degenerative myelopathy, a disease model of amyotrophic lateral sclerosis

Targeting of the CB₂ receptor results in neuroprotection in the SOD1^G93A mutant mouse model of amyotrophic lateral sclerosis (ALS). The neuroprotective effects of CB₂ receptors are facilitated by their upregulation in the spinal cord of the mutant mice. Here, we investigated whether similar CB₂ receptor upregulation, as well as parallel changes in other endocannabinoid elements, is evident in the spinal cord of dogs with degenerative myelopathy (DM), caused by mutations in the superoxide dismutase 1 gene (SOD1). We used well-characterized post-mortem spinal cords from unaffected and DM-affected dogs. Tissues were used first to confirm the loss of motor neurons using Nissl staining, which was accompanied by glial reactivity (elevated GFAP and Iba-1 immunoreactivity). Next, we investigated possible differences in the expression of endocannabinoid genes measured by qPCR between DM-affected and control dogs. We found no changes in expression of the CB₁ receptor (confirmed with CB₁ receptor immunostaining) or NAPE-PLD, DAGL, FAAH and MAGL enzymes. In contrast, CB₂ receptor levels were significantly elevated in DM-affected dogs determined by qPCR and western blotting, which was confirmed in the grey matter using CB₂ receptor immunostaining. Using double-labelling immunofluorescence, CB₂ receptor immunolabelling colocalized with GFAP but not Iba-1, indicating upregulation of CB₂ receptors on astrocytes in DM-affected dogs. Our results demonstrate a marked upregulation of CB₂ receptors in the spinal cord in canine DM, which is concentrated in activated astrocytes. Such receptors could be used as a potential target to enhance the neuroprotective effects exerted by these glial cells.

Editors' choice: CB₂ receptors are upregulated in activated astrocytes recruited at the damaged spinal cord in dogs with degenerative myelopathy, a canine model of amyotrophic lateral sclerosis.

AAV gene transfer delays disease onset in a TPP1-deficient canine model of the late infantile form of Batten disease

The most common form of the childhood neurodegenerative disease late infantile neuronal ceroid lipofuscinosis (also called Batten disease) is caused by deficiency of the soluble lysosomal enzyme tripeptidyl peptidase 1 (TPP1) resulting from mutations in the TPP1 gene. We tested whether TPP1 gene transfer to the ependyma, the epithelial lining of the brain ventricular system, in TPP1-deficient dogs would be therapeutically beneficial. A one-time administration of recombinant adeno-associated virus (rAAV) expressing canine TPP1 (rAAV.caTPP1) resulted in high expression of TPP1 predominantly in ependymal cells and secretion of the enzyme into the cerebrospinal fluid leading to clinical benefit. Diseased dogs treated with rAAV.caTPP1 showed delays in onset of clinical signs and disease progression, protection from cognitive decline, and extension of life span. By immunostaining and enzyme assay, recombinant protein was evident throughout the brain and spinal cord, with correction of the neuropathology characteristic of the disease. This study in a naturally occurring canine model of TPP1 deficiency highlights the utility of AAV transduction of ventricular lining cells to accomplish stable secretion of recombinant protein for broad distribution in the central nervous system and therapeutic benefit.

A One Health overview, facilitating advances in comparative medicine and translational research

A1 One health advances and successes in comparative medicine and translational research

Cheryl Stroud

A2 Dendritic cell-targeted gorilla adenoviral vector for cancer vaccination for canine melanoma

Igor Dmitriev, Elena Kashentseva, Jeffrey N. Bryan, David T. Curiel

A3 Viroimmunotherapy for malignant melanoma in the companion dog model

Jeffrey N. Bryan, David Curiel, Igor Dmitriev, Elena Kashentseva, Hans Rindt, Carol Reinero, Carolyn J. Henry

A4 Of mice and men (and dogs!): development of a commercially licensed xenogeneic DNA vaccine for companion animals with malignant melanoma

Philip J. Bergman

A5 Successful immunotherapy with a recombinant HER2-expressing Listeria monocytogenes in dogs with spontaneous osteosarcoma paves the way for advances in pediatric osteosarcoma

Nicola J. Mason, Josephine S. Gnanandarajah, Julie B. Engiles, Falon Gray, Danielle Laughlin, Anita Gaurnier-Hausser, Anu Wallecha, Margie Huebner, Yvonne Paterson

A6 Human clinical development of ADXS-HER2

Daniel O’Connor

A7 Leveraging use of data for both human and veterinary benefit

Laura S. Treml

A8 Biologic replacement of the knee: innovations and early clinical results

James P. Stannard

A9 Mizzou BioJoint Center: a translational success story

James L. Cook

A10 University and industry translational partnership: from the lab to commercialization

Marc Jacobs

A11 Beyond docking: an evolutionarily guided OneHealth approach to drug discovery

Gerald J. Wyckoff, Lee Likins, Ubadah Sabbagh, Andrew Skaff

A12 Challenges and opportunities for data applications in animal health: from precision medicine to precision husbandry

Amado S. Guloy

A13 A cloud-based programmable platform for health

Harlen D. Hays

A14 Comparative oncology: One Health in action

Amy K. LeBlanc

A15 Companion animal diseases bridge the translational gap for human neurodegenerative disease

Joan R. Coates, Martin L. Katz, Leslie A. Lyons, Gayle C. Johnson, Gary S. Johnson, Dennis P. O’Brien

A16 Duchenne muscular dystrophy gene therapy

Dongsheng Duan

A17 Polycystic kidney disease: cellular mechanisms to emerging therapies

James P. Calvet

A18 The domestic cat as a large animal model for polycystic kidney disease

Leslie A. Lyons, Barbara Gandolfi

A19 The support of basic and clinical research by the Polycystic Kidney Disease Foundation

David A. Baron

A20 Using naturally occurring large animal models of human disease to enable clinical translation: treatment of arthritis using autologous stromal vascular fraction in dogs

Mark L. Weiss

A21 Regulatory requirements regarding clinical use of human cells, tissues, and tissue-based products

Debra A. Webster

A22 Regenerative medicine approaches to Type 1 diabetes treatment

Francis N. Karanu

A23 The zoobiquity of canine diabetes mellitus, man’s best friend is a friend indeed-islet transplantation

Edward J. Robb

A24 One Medicine: a development model for cellular therapy of diabetes

Robert J. Harman

Nonclinical evaluation of CNS-administered TPP1 enzyme replacement in canine CLN2 neuronal ceroid lipofuscinosis

The CLN2 form of neuronal ceroid lipofuscinosis, a type of Batten disease, is a lysosomal storage disorder caused by a deficiency of the enzyme tripeptidyl peptidase-1 (TPP1). Patients exhibit progressive neurodegeneration and loss of motor, cognitive, and visual functions, leading to death by the early teenage years. TPP1-null Dachshunds recapitulate human CLN2 disease. To characterize the safety and pharmacology of recombinant human (rh) TPP1 administration to the cerebrospinal fluid (CSF) as a potential enzyme replacement therapy (ERT) for CLN2 disease, TPP1-null and wild-type (WT) Dachshunds were given repeated intracerebroventricular (ICV) infusions and the pharmacokinetic (PK) profile, central nervous system (CNS) distribution, and safety were evaluated. TPP1-null animals and WT controls received 4 or 16mg of rhTPP1 or artificial cerebrospinal fluid (aCSF) vehicle every other week. Elevated CSF TPP1 concentrations were observed for 2-3 days after the first ICV infusion and were approximately 1000-fold higher than plasma levels at the same time points. Anti-rhTPP1 antibodies were detected in CSF and plasma after repeat rhTPP1 administration, with titers generally higher in TPP1-null than in WT animals. Widespread brain distribution of rhTPP1 was observed after chronic administration. Expected histological changes were present due to the CNS delivery catheters and were similar in rhTPP1 and vehicle-treated animals, regardless of genotype. Neuropathological evaluation demonstrated the clearance of lysosomal storage, preservation of neuronal morphology, and reduction in brain inflammation with treatment. This study demonstrates the favorable safety and pharmacology profile of rhTPP1 ERT administered directly to the CNS and supports clinical evaluation in patients with CLN2 disease.

Enzyme replacement therapy attenuates disease progression in a canine model of late-infantile neuronal ceroid lipofuscinosis (CLN2 disease)

Using a canine model of classical late-infantile neuronal ceroid lipofuscinosis (CLN2 disease), a study was conducted to evaluate the potential pharmacological activity of recombinant human tripeptidyl peptidase-1 (rhTPP1) enzyme replacement therapy administered directly to the cerebrospinal fluid (CSF). CLN2 disease is a hereditary neurodegenerative disorder resulting from mutations in CLN2, which encodes the soluble lysosomal enzyme tripeptidyl peptidase-1 (TPP1). Infants with mutations in both CLN2 alleles develop normally but in the late-infantile/early-childhood period undergo progressive neurological decline accompanied by pronounced brain atrophy. The disorder, a form of Batten disease, is uniformly fatal, with clinical signs starting between 2 and 4 years of age and death usually occurring by the early teenage years. Dachshunds homozygous for a null mutation in the canine ortholog of CLN2 (TPP1) exhibit a similar disorder that progresses to end stage at 10.5–11 months of age. Administration of rhTPP1 via infusion into the CSF every other week, starting at approximately 2.5 months of age, resulted in dose-dependent significant delays in disease progression, as measured by delayed onset of neurologic deficits, improved performance on a cognitive function test, reduced brain atrophy, and increased life span. Based on these findings, a clinical study evaluating the potential therapeutic value of rhTPP1 administration into the CSF of children with CLN2 disease has been initiated.

A homozygous KCNJ10 mutation in Jack Russell Terriers and related breeds with spinocerebellar ataxia with myokymia, seizures, or both

Background

Juvenile‐onset spinocerebellar ataxia has been recognized in Jack Russell Terriers and related Russell group terriers (RGTs) for over 40 years. Ataxia occurs with varying combinations of myokymia, seizures, and other signs of neurologic disease. More than 1 form of the disease has been suspected.

Hypothesis/Objectives

The objective was to identify the mutation causing the spinocerebellar ataxia associated with myokymia, seizures, or both and distinguish the phenotype from other ataxias in the RGTs.

Animals

DNA samples from 16 RGTs with spinocerebellar ataxia beginning from 2 to 12 months of age, 640 control RGTs, and 383 dogs from 144 other breeds along with the medical records of affected dogs were studied.

Methods

This case‐control study compared the frequencies of a KCNJ10 allele in RGTs with spinocerebellar ataxia versus control RGTs. This allele was identified in a whole‐genome sequence of a single RGT with spinocerebellar ataxia and myokymia by comparison to whole‐genome sequences from 81 other canids that were normal or had other diseases.

Results

A missense mutation in the gene coding for the inwardly rectifying potassium channel Kir4.1 (KCNJ10:c.627C>G) was significantly (P < .001) associated with the disease. Dogs homozygous for the mutant allele all had spinocerebellar ataxia with varying combinations of myokymia and seizures.

Conclusions and Clinical Importance

Identification of the KCNJ10 mutation in dogs with spinocerebellar ataxia with myokymia, seizures, or both clarifies the multiple forms of ataxia seen in these breeds and provides a DNA test to identify carriers.

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.

Diagnostic immunohistochemistry of canine and feline intracalvarial tumors in the age of brain biopsies

The focus of immunohistochemistry as applied to nervous system tumors is in identifying the neoplasm present and evaluating margins between normal and neoplastic tissue. Although not always utilized by specialists in neuropathology, immunohistochemistry remains useful to resolve concerns about the differentiation and rate of tumor growth. The aims of this review are to discuss the utility of immunohistochemical reagents currently used in diagnosis of canine and feline intracalvarial tumors, to indicate the applicability of some tests currently used in human nervous system tumors for domestic species, and to evaluate a few less commonly used reagents. A panel of biomarkers is usually needed to confirm a diagnosis, with groups of reagents for leptomeningeal, intraparenchymal, and ventricular neoplasms. In the future, signature genetic alterations found among feline and canine brain tumors--as correlated prospectively with diagnosis, rate of enlargement, or response to treatment--may result in new immunohistochemical reagents to simplify the task of diagnosis. Prospective studies determining the type and proportion of stem cell marker expression on patient longevity are likely to be fruitful and suggest new therapies. Due to increased frequency of biopsy or partial resection of tumors from the living patient, biomarkers are needed to serve as accurate prognostic indicators and assist in determining the efficacy of developing therapeutic options in nervous system tumors of dogs and cats.

Effect of treatment with simvastatin and cyclosporine on neurotransmitter concentrations in cerebrospinal fluid after subarachnoid hemorrhage in dogs

OBJECTIVE

To measure concentrations of glutamate, aspartate, γ-aminobutyric acid (GABA), and glycine in CSF of dogs with experimentally induced subarachnoid hemorrhage (SAH) and to assess effects of cyclosporine and simvastatin on these concentrations.

SAMPLE

CSF samples from 13 dogs.

PROCEDURES

In a previous study, SAH was induced in dogs via 2 injections of autologous blood into the cerebellomedullary cistern 24 hours apart. Dogs were untreated (control; n = 5) or received simvastatin alone (4) or simvastatin in combination with cyclosporine (4). Samples of CSF were collected before the first blood injection (baseline; time 0), before the second blood injection, and on days 3, 7, and 10. For the study reported here, neurotransmitter concentrations in CSF were analyzed via high-performance liquid chromatography. Data were analyzed with a repeated-measures model with adjustments for multiple comparisons by use of the Tukey method.

RESULTS

In control dogs, the glutamate concentration peaked on day 3 and there was a significant increase in GABA and glutamate concentrations. Glutamate concentrations were significantly lower and glycine concentrations significantly higher on day 3 after administration of simvastatin alone or simvastatin in combination with cyclosporine, compared with concentrations for the control group. No significant differences in GABA and aspartate concentrations were detected among treatment groups at any time point.

CONCLUSIONS AND CLINICAL RELEVANCE

Glutamate concentrations were increased in the CSF of dogs with SAH. Simvastatin administration attenuated high glutamate concentrations. A combination of immunosuppression and upregulation of nitric oxide synthase may be useful in lowering high glutamate concentrations in ischemic CNS conditions.

Pupillary light reflex deficits in a canine model of late infantile neuronal ceroid lipofuscinosis

Late-infantile neuronal ceroid lipofuscinosis (CLN2) is a hereditary neurological disorder characterized by progressive retinal degeneration and vision loss, cognitive and motor decline, seizures, and pronounced brain atrophy. The progressive loss of neurological functions eventually leads to death, usually by the early teenage years. Utilizing a canine model of CLN2, therapeutic studies to inhibit the brain and retinal degenerations are currently under way. Using this dog model, studies were undertaken to compare quantitative assessments of the pupillary light reflex (PLR) and electroretinography (ERG) as tools for evaluating the effects of the disease on retinal function. The PLR and ERG were recorded in normal and CLN2-affected Dachshunds at 2 month intervals between the ages of 4 and 10 months. Using custom instrumentation for quantitative PLR assessments, a series of white light stimuli of varying intensity was used to elicit pupil constriction, and pupil images were recorded using continuous infrared illumination and an infrared-sensitive camera. Electroretinography was used to evaluate retinal function in the same dogs. As the disease progressed, affected dogs exhibited progressive and profound declines in ERG amplitudes under both scotopic and photopic conditions. With low intensity light stimuli, CLN2 was also accompanied by progressive deficits in the PLR. Changes in the PLR to dim light stimuli included significant deficits in latency, constriction velocity, constriction amplitude, and redilation velocity. However, despite the almost complete loss of detectable ERG responses by disease end stage, the PLR to bright stimuli was well preserved throughout the disease progression. These findings demonstrate that the PLR is much more sensitive than the ERG in detecting residual retinal function in animal models of retinal degenerative disease. The preservation of the PLR in dogs with profoundly depressed ERGs correlates with a preservation of visually-mediated behavior even late in the disease progression. Quantitative analysis of the PLR has potential as a biomarker in animal models of retinal degenerative diseases and in evaluating the efficacy of therapeutic interventions in preserving retinal function.

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.

Quantitative assessment of the canine pupillary light reflex

PURPOSE

To develop instrumentation and methods for thorough quantitative assessment of the pupillary light reflex (PLR) in dogs under varying stimulus conditions.

METHODS

The PLR was recorded in normal Dachshunds using a custom system allowing full user control over stimulus intensity, color, and duration. Chemical restraint protocols were compared to determine which protocol provided for optimal baseline stability of pupil size and appropriate eye positioning. A series of white light stimuli of increasing intensity was used to elicit pupil constriction. Pupil images were concurrently recorded using continuous infrared illumination and an infrared-sensitive camera. The PLR was also recorded in response to blue and red stimuli.

RESULTS

With injectable chemical restraint alone, spontaneous fluctuations in pupil size occurred independent of light stimulation, and spontaneous eye movements made it difficult to fully visualize the pupil. Combined injectable chemical and inhalation restraint provided a steady baseline pupil size throughout PLR assessment and allowed for stable positioning of the eye using a conjunctival stay suture. Robust PLRs were elicited with all light colors. PLR constriction amplitude increased with increasing flash intensity and ranged from 5% to 70%.

CONCLUSIONS

A recording system and protocol have been developed to reliably quantify the canine PLR. The techniques and instrumentation will be useful for objective quantitative assessment of the PLR in dogs and other species in research applications and may be useful in clinical veterinary ophthalmology and neurology if PLR abnormalities detected with these procedures can be associated with specific 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.

Intrathecal tripeptidyl-peptidase 1 reduces lysosomal storage in a canine model of late infantile neuronal ceroid lipofuscinosis

Late infantile neuronal ceroid lipofuscinosis (LINCL) is caused by mutations in the gene encoding tripeptidyl-peptidase 1 (TPP1). LINCL patients accumulate lysosomal storage materials in the CNS accompanied by neurodegeneration, blindness, and functional decline. Dachshunds homozygous for a null mutation in the TPP1 gene recapitulate many symptoms of the human disease. The objectives of this study were to determine whether intrathecal (IT) TPP1 treatment attenuates storage accumulation and functional decline in TPP1-/- Dachshunds and to characterize the CNS distribution of TPP1 activity. TPP1 was administered to one TPP1-/- and one homozygous wild-type (WT) dog. An additional TPP1-/- and WT dog received vehicle. Four IT administrations of 32 mg TPP1 formulated in 2.3 mL of artificial cerebrospinal fluid (aCSF) or vehicle were administered monthly via the cerebellomedullary cistern from four to seven months of age. Functional decline was assessed by physical and neurological examinations, electrophysiology, and T-maze performance. Neural tissues were collected 48 h after the fourth administration and analyzed for TPP1 activity and autofluorescent storage material. TPP1 was distributed at greater than WT levels in many areas of the CNS of the TPP1-/- dog administered TPP1. The amount of autofluorescent storage was decreased in this dog relative to the vehicle-treated affected control. No improvement in overall function was observed in this dog compared to the vehicle-treated TPP1-/- littermate control. These results demonstrate for the first time in a large animal model of LINCL widespread delivery of biochemically active TPP1 to the brain after IT administration along with a decrease in lysosomal storage material. Further studies with this model will be necessary to optimize the dosing route and regimen to attenuate functional decline.

A reversal learning task detects cognitive deficits in a Dachshund model of late-infantile neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs) are autosomal recessive lysosomal storage diseases characterized by progressive neurodegeneration and by accumulation of autofluorescent storage material in the central nervous system and other tissues. One of the most prominent clinical signs of NCL is progressive decline in cognitive function. We previously described a frame shift mutation of TPP1 in miniature long-haired Dachshunds which causes an early-onset form of NCL analogous to classical late-infantile onset NCL (CLN2) in children. Dogs homozygous for the TPP1 mutation exhibit progressive neurological signs similar to those exhibited by human patients. In order to establish biomarkers for evaluating the efficacy of ongoing therapeutic studies in this canine model, we characterized phenotypic changes in 13 dogs through 9 months of age. Cognitive function was assessed using a T-maze reversal learning (RL) task. Cognitive dysfunction was detected in affected dogs as early as 6 months of age and worsened as the disease progressed. Physical and neurological examination, funduscopy and electroretinography (ERG) were performed at regular intervals. Only the changes in ERG responses showed signs of disease progression earlier than the RL task. In the later stages of the disease clinical signs of visual and motor deficits became evident. The visual and motor deficits were not severe enough to affect the performance of dogs in the T-maze. Declining performance on the RL task is a sensitive measure of higher-order cognitive dysfunction which can serve as a useful biomarker of disease progression.

Characterization and mode of inheritance of a paroxysmal dyskinesia in Chinook dogs

BACKGROUND

Paroxysmal dyskinesias are episodes of abnormal, involuntary movement or muscle tone, distinguished from seizures by the character of the episode and lack of seizure activity on ictal EEG.

HYPOTHESIS

Paroxysmal dyskinesia is an inherited, autosomal recessive disorder in Chinook dogs.

ANIMALS

Families of Chinook dogs with paroxysmal dyskinesia.

METHODS

Pedigrees and medical histories were reviewed for 299 Chinook dogs. A family of 51 dogs was used for analysis. Episodes were classified as seizures, paroxysmal dyskinesia, or unknown, and segregation analysis was performed.

RESULTS

Paroxysmal dyskinesia was identified in 16 of 51 dogs and characterized by an inability to stand or ambulate, head tremors, and involuntary flexion of 1 or multiple limbs, without autonomic signs or loss of consciousness. Episode duration varied from minutes to an hour. Inter-ictal EEGs recorded on 2 dogs with dyskinesia were normal. Three dogs with dyskinesia also had generalized tonic-clonic seizures. One of 51 dogs had episodes of undetermined type. Phenotype was unknown for 6 of 51 dogs, and 28 dogs were unaffected. Segregation was consistent with an autosomal recessive trait.

CONCLUSIONS AND CLINICAL IMPORTANCE

This movement disorder is prevalent in the Chinook breed, and consistent with a partially penetrant autosomal recessive or polygenic trait. Insufficient evidence exists for definitive localization; episodes may be of basal nuclear origin, but atypical seizures and muscle membrane disorders remain possible etiologies. The generalized seizures may be a variant phenotype of the same mutation that results in dyskinesia, or the 2 syndromes may be independent.

A truncated retrotransposon disrupts the GRM1 coding sequence in Coton de Tulear dogs with Bandera's neonatal ataxia

BACKGROUND

Bandera's neonatal ataxia (BNAt) is an autosomal recessive cerebellar ataxia that affects members of the Coton de Tulear dog breed.

OBJECTIVE

To identify the mutation that causes BNAt.

ANIMALS

The study involved DNA from 112 Cotons de Tulear (including 15 puppies with signs of BNAt) and 87 DNA samples from dogs of 12 other breeds.

METHODS

The BNAt locus was mapped with a genome-wide association study (GWAS). The coding exons of positional candidate gene GRM1, which encodes metabotropic glutamate receptor 1, were polymerase chain reaction (PCR)-amplified and resequenced. A 3-primer PCR assay was used to genotype individual dogs for a truncated retrotransposon inserted into exon 8 of GRM1.

RESULTS

The GWAS indicated that the BNAt locus was in a canine chromosome 1 region that contained candidate gene GRM1. Resequencing this gene from BNAt-affected puppies indicated that exon 8 was interrupted by the insertion of a 5'-truncated retrotransposon. All 15 BNAt-affected puppies were homozygous for the insert, whereas all other Cotons de Tulear were heterozygotes (n = 43) or homozygous (n = 54) for the ancestral allele. None of the 87 dogs from 12 other breeds had the insertion allele.

CONCLUSIONS AND CLINICAL IMPORTANCE

BNAt is caused by a retrotransposon inserted into exon 8 of GRM1. A DNA test for the GRM1 retrotransposon insert can be used for genetic counseling and to confirm the diagnosis of BNAt.