Pathological findings in a Dachshund-cross dog with neuroaxonal dystrophy

Phenotypic and genetic aspects of hereditary ataxia in dogs

Hereditary ataxias are a large group of neurodegenerative diseases that have cerebellar or spinocerebellar dysfunction as core feature, occurring as an isolated sign or as part of a syndrome. Based on neuropathology, this group of diseases has so far been classified into cerebellar cortical degenerations, spinocerebellar degenerations, cerebellar ataxias without substantial neurodegeneration, canine multiple system degeneration, and episodic ataxia. Several new hereditary ataxia syndromes are described, but most of these diseases have similar clinical signs and unspecific diagnostic findings, wherefore achieving a definitive diagnosis in these dogs is challenging. Eighteen new genetic variants associated with these diseases have been discovered in the last decade, allowing clinicians to reach a definitive diagnosis for most of these conditions, and allowing breeding schemes to adapt to prevent breeding of affected puppies. This review summarizes the current knowledge about hereditary ataxias in dogs, and proposes to add a "multifocal degenerations with predominant (spino)cerebellar component" category regrouping canine multiple system degeneration, new hereditary ataxia syndromes that do not fit in 1 of the previous categories, as well as specific neuroaxonal dystrophies and lysosomal storage diseases that cause major (spino)cerebellar dysfunction.

Heterogeneous immunoreactivity of axonal spheroids in focal symmetrical encephalomalacia produced by Clostridium perfringens type D epsilon toxin in sheep

Since axonal injury (AI) is an important component of many veterinary neurologic disorders, we assessed the relative ability of a panel of antibodies (amyloid precursor protein, 3 subunits of neurofilament protein, protein gene product 9.5, ubiquitin, and synaptophysin) to detect axonal swellings or spheroids. Abundant axonal spheroids found in necrotic internal capsule foci produced in 4 sheep by chronic Clostridium perfringens type D epsilon neurotoxicity provided a model system in which to evaluate this important diagnostic tool. There was heterogeneous labeling of subsets of spheroids by the respective antibodies, suggesting that, in order to detect the complete spectrum of AI in diagnostic cases, a range of antibodies should be used, not only when spheroids are plentiful but also when they are few in number or incompletely developed. The application of insufficient markers in the latter cases can potentially lead to the contribution of AI to lesion pathogenesis being underappreciated.

Accuracy of selected neurological clinical tests in diagnosing MRI-detectable forebrain lesion in dogs

This retrospective case study aims to evaluate the accuracy of menace response, response to nasal stimulation and proprioceptive placing in diagnosing forebrain lesion in dogs. A total of 145 client-owned dogs investigated by magnetic resonance imaging study of the brain between December 2017 and June 2019 were evaluated. Seventy-one dogs with no magnetic resonance imaging-detectable intracranial and significant cerebrospinal fluid abnormality or recent history of seizure (<48 h) served as controls. Binary regression analysis was performed to determine the sensitivity, specificity and likelihood ratios of each selected test. Older age at presentation was a significant risk factor for the presence of a forebrain lesion. Menace (62.5%) and proprioceptive deficits (40.5%) were common findings in all dogs. They were also significantly associated with the presence of forebrain abnormality. Moreover, they were more sensitive (77.3% and 82.2%, respectively) and specific (50.0% and 62.5%, respectively) when applied to dogs aged 6 years or older. Nonetheless, all of these tests' likelihood ratios, and thus reliability are poor. These neurological tests are commonly employed for diagnosing forebrain disease in dogs, yet are not highly accurate in diagnosing forebrain abnormality. Clinicians should interpret these clinical test results along with the patient history when designing a diagnostic plan.

Spontaneous Axonal Dystrophy in the Brain and Spinal Cord in Naïve Beagle Dogs

Axonal dystrophy (AD) is a common age-related neurohistological finding in vertebrates that can be congenital or induced by xenobiotics, vitamin E deficiency, or trauma/compression. To understand the incidence and location of AD as a background finding in Beagle dogs used in routine toxicity studies, we examined central nervous system (CNS) and selected peripheral nervous system (PNS) tissues in twenty 18- to 24-month-old and ten 4- to 5-year-old control males and females. Both sexes were equally affected. The cuneate, gracile, and cochlear nuclei and the cerebellar white matter (rostral vermis) were the most common locations for AD. Incidence of AD increased with age in the cuneate nucleus, cerebellar white matter (rostral vermis), trigeminal nuclei/tracts, and lumbar spinal cord. Axonal dystrophy in the CNS was not accompanied by neuronal degeneration/necrosis, nerve fiber degeneration, and/or glial reaction. Axonal dystrophy was not observed in the PNS (sciatic nerve, vagus nerve branches, or gastrointestinal mural autonomic plexuses).

A Missense Mutation in the Vacuolar Protein Sorting 11 (VPS11) Gene Is Associated with Neuroaxonal Dystrophy in Rottweiler Dogs

Canine neuroaxonal dystrophy (NAD) is a recessive, degenerative neurological disease of young adult Rottweiler dogs (Canis lupus familiaris) characterized pathologically by axonal spheroids primarily targeting sensory axon terminals. A genome-wide association study of seven Rottweilers affected with NAD and 42 controls revealed a significantly associated region on canine chromosome 5 (CFA 5). Homozygosity within the associated region narrowed the critical interval to a 4.46 Mb haplotype (CFA5:11.28 Mb – 15.75 Mb; CanFam3.1) that associated with the phenotype. Whole-genome sequencing of two histopathologically confirmed canine NAD cases and 98 dogs unaffected with NAD revealed a homozygous missense mutation within the Vacuolar Protein Sorting 11 (VPS11) gene (g.14777774T > C; p.H835R) that was associated with the phenotype. These findings present the opportunity for an antemortem test for confirming NAD in Rottweilers where the allele frequency was estimated at 2.3%. VPS11 mutations have been associated with a degenerative leukoencephalopathy in humans, and VSP11 should additionally be included as a candidate gene for unexplained cases of human NAD.

Ultrastructural features of canine neuroaxonal dystrophy in a Papillon dog

Neuroaxonal dystrophy (NAD) is a neurodegenerative disease characterized by severe axonal swelling (spheroids) throughout the nervous system. In dogs, NAD has been reported in several breeds and a missense mutation in PLA2G6 gene has recently been identified in the Papillon dog NAD. Here we performed ultrastructural analysis to clarify the detailed ultrastructural features of the Papillon dog NAD. Dystrophic axons consisted of accumulation of filamentous materials, tubulovesicular structures, and swollen edematous mitochondria with degenerated inner membranes were often observed in the central nervous system. At axonal terminals, degeneration of presynaptic membrane was also detected. As reported in Pla2g6 knockout mice, mitochondrial and presynaptic degeneration may be related with the pathogenesis of NAD in Papillon dogs.

Identification of the PLA2G6 c.1579G>A Missense Mutation in Papillon Dog Neuroaxonal Dystrophy Using Whole Exome Sequencing Analysis

Whole exome sequencing (WES) has become a common tool for identifying genetic causes of human inherited disorders, and it has also recently been applied to canine genome research. We conducted WES analysis of neuroaxonal dystrophy (NAD), a neurodegenerative disease that sporadically occurs worldwide in Papillon dogs. The disease is considered an autosomal recessive monogenic disease, which is histopathologically characterized by severe axonal swelling, known as “spheroids,” throughout the nervous system. By sequencing all eleven DNA samples from one NAD-affected Papillon dog and her parents, two unrelated NAD-affected Papillon dogs, and six unaffected control Papillon dogs, we identified 10 candidate mutations. Among them, three candidates were determined to be “deleterious” by in silico pathogenesis evaluation. By subsequent massive screening by TaqMan genotyping analysis, only the PLA2G6 c.1579G>A mutation had an association with the presence or absence of the disease, suggesting that it may be a causal mutation of canine NAD. As a human homologue of this gene is a causative gene for infantile neuroaxonal dystrophy, this canine phenotype may serve as a good animal model for human disease. The results of this study also indicate that WES analysis is a powerful tool for exploring canine hereditary diseases, especially in rare monogenic hereditary diseases.