Cross-Species Single-Cell Analysis Reveals Divergence of the Primate Microglia Program.

Microglia, the brain-resident immune cells, are critically involved in many physiological and pathological brain processes, including neurodegeneration. Here we characterize microglia morphology and transcriptional programs across ten species spanning more than 450 million years of evolution. We find that microglia express a conserved core gene program of orthologous genes from rodents to humans, including ligands and receptors associated with interactions between glia and neurons. In most species, microglia show a single dominant transcriptional state, whereas human microglia display significant heterogeneity. In addition, we observed notable differences in several gene modules of rodents compared with primate microglia, including complement, phagocytic, and susceptibility genes to neurodegeneration, such as Alzheimer's and Parkinson's disease. Our study provides an essential resource of conserved and divergent microglia pathways across evolution, with important implications for future development of microglia-based therapies in humans.

Intragenic duplication disrupting the reading frame of MFSD8 in Small Swiss Hounds with neuronal ceroid lipofuscinosis.

Neuronal ceroid lipofuscinosis (NCL) represents a heterogenous group of lysosomal storage diseases resulting in progressive neurodegeneration. We investigated two Small Swiss Hound littermates that showed progressive ataxia and loss of cognitive functions and vision starting around the age of 12 months. Both dogs had to be euthanized a few months after the onset of disease owing to the severity of their clinical signs. Pathological investigation of one affected dog revealed cerebral and cerebellar atrophy with cytoplasmic accumulation of autofluorescent material in degenerating neurons. The clinical signs in combination with the characteristic histopathology led to a tentative diagnosis of NCL. In the subsequent genetic investigation, the genome of one affected dog was sequenced. This revealed a duplication of 18 819 bp within the MFSD8 gene. The duplication breakpoints were located in intron 3 and exon 12 of the gene and were predicted to disrupt the reading frame. Both affected dogs carried the duplication in a homozygous state and there was perfect cosegregation of the genotypes with the phenotype in a large pedigree, consistent with autosomal recessive inheritance. MFSD8 loss-of-function variants are a known cause of NCL7 in human patients, dogs and other mammalian species. The existing knowledge on MFSD8 together with the experimental data strongly suggests that the identified intragenic MFSD8 duplication caused the disease in the Small Swiss Hounds. These results allow their diagnosis to be refined to NCL7 and enable genetic testing in the breed to avoid further unintentional carrier × carrier matings.

Intradural-extramedullary inflammatory pseudotumour of the cervical spinal cord of a dog.

An 8-year-old mixed-breed dog was presented with cervical hyperesthesia, tetraparesis, and mild proprioceptive ataxia in all four limbs. 3 Tesla MRI showed a dorsal compressive intradural-extramedullary mass at the level of C1-C2, isointense to the gray matter with a hypointense ventral core on T2 weighted images (WI), isointense on T1WI, with a strong and homogeneous contrast enhancement. A C1-C2 partial dorsal laminectomy was performed, and the lesion was removed en bloc. The histopathological and immunohistochemical analysis defined the diagnosis of inflammatory pseudotumor.

A loss-of-function variant in canine GLRA1 associates with a neurological disorder resembling human hyperekplexia.

Hereditary hyperekplexia is a rare neuronal disorder characterized by an exaggerated startle response to sudden tactile or acoustic stimuli. In this study, we present a Miniature Australian Shepherd family showing clinical signs, which have genetic and phenotypic similarities with human hereditary hyperekplexia: episodes of muscle stiffness that could occasionally be triggered by acoustic stimuli. Whole genome sequence data analysis of two affected dogs revealed a 36-bp deletion spanning the exon-intron boundary in the glycine receptor alpha 1 (GLRA1) gene. Further validation in pedigree samples and an additional cohort of 127 Miniature Australian Shepherds, 45 Miniature American Shepherds and 74 Australian Shepherds demonstrated complete segregation of the variant with the disease, according to an autosomal recessive inheritance pattern. The protein encoded by GLRA1 is a subunit of the glycine receptor, which mediates postsynaptic inhibition in the brain stem and spinal cord. The canine GLRA1 deletion is located in the signal peptide and is predicted to cause exon skipping and subsequent premature stop codon resulting in a significant defect in glycine signaling. Variants in GLRA1 are known to cause hereditary hyperekplexia in humans; however, this is the first study to associate a variant in canine GLRA1 with the disorder, establishing a spontaneous large animal disease model for the human condition.

Characterisation of canine KCNIP4: A novel gene for cerebellar ataxia identified by whole-genome sequencing two affected Norwegian Buhund dogs.

A form of hereditary cerebellar ataxia has recently been described in the Norwegian Buhund dog breed. This study aimed to identify the genetic cause of the disease. Whole-genome sequencing of two Norwegian Buhund siblings diagnosed with progressive cerebellar ataxia was carried out, and sequences compared with 405 whole genome sequences of dogs of other breeds to filter benign common variants. Nine variants predicted to be deleterious segregated among the genomes in concordance with an autosomal recessive mode of inheritance, only one of which segregated within the breed when genotyped in additional Norwegian Buhunds. In total this variant was assessed in 802 whole genome sequences, and genotyped in an additional 505 unaffected dogs (including 146 Buhunds), and only four affected Norwegian Buhunds were homozygous for the variant. The variant identified, a T to C single nucleotide polymorphism (SNP) (NC_006585.3:g.88890674T>C), is predicted to cause a tryptophan to arginine substitution in a highly conserved region of the potassium voltage-gated channel interacting protein KCNIP4. This gene has not been implicated previously in hereditary ataxia in any species. Evaluation of KCNIP4 protein expression through western blot and immunohistochemical analysis using cerebellum tissue of affected and control dogs demonstrated that the mutation causes a dramatic reduction of KCNIP4 protein expression. The expression of alternative KCNIP4 transcripts within the canine cerebellum, and regional differences in KCNIP4 protein expression, were characterised through RT-PCR and immunohistochemistry respectively. The voltage-gated potassium channel protein KCND3 has previously been implicated in spinocerebellar ataxia, and our findings suggest that the Kv4 channel complex KCNIP accessory subunits also have an essential role in voltage-gated potassium channel function in the cerebellum and should be investigated as potential candidate genes for cerebellar ataxia in future studies in other species.

In-frame deletion in canine PITRM1 is associated with a severe early-onset epilepsy, mitochondrial dysfunction and neurodegeneration.

We investigated the clinical, genetic, and pathological characteristics of a previously unknown severe juvenile brain disorder in several litters of Parson Russel Terriers. The disease started with epileptic seizures at 6-12 weeks of age and progressed rapidly to status epilepticus and death or euthanasia. Histopathological changes at autopsy were restricted to the brain. There was severe acute neuronal degeneration and necrosis diffusely affecting the grey matter throughout the brain with extensive intraneuronal mitochondrial crowding and accumulation of amyloid-ß (Aß). Combined homozygosity mapping and genome sequencing revealed an in-frame 6-bp deletion in the nuclear-encoded pitrilysin metallopeptidase 1 (PITRM1) encoding for a mitochondrial protease involved in mitochondrial targeting sequence processing and degradation. The 6-bp deletion results in the loss of two amino acid residues in the N-terminal part of PITRM1, potentially affecting protein folding and function. Assessment of the mitochondrial function in the affected brain tissue showed a significant deficiency in respiratory chain function. The functional consequences of the mutation were modeled in yeast and showed impaired growth in permissive conditions and an impaired respiration capacity. Loss-of-function variants in human PITRM1 result in a childhood-onset progressive amyloidotic neurological syndrome characterized by spinocerebellar ataxia with behavioral, psychiatric and cognitive abnormalities. Homozygous Pitrm1-knockout mice are embryonic lethal, while heterozygotes show a progressive, neurodegenerative phenotype characterized by impairment in motor coordination and Aß deposits. Our study describes a novel early-onset PITRM1-related neurodegenerative canine brain disorder with mitochondrial dysfunction, Aß accumulation, and lethal epilepsy. The findings highlight the essential role of PITRM1 in neuronal survival and strengthen the connection between mitochondrial dysfunction and neurodegeneration.

Demyelinating polyneuropathy in goats lacking prion protein.

Studies in mice with ablation of Prnp, the gene that encodes the cellular prion protein (PrPC ), have led to the hypothesis that PrPC is important for peripheral nerve myelin maintenance. Here, we have used a nontransgenic animal model to put this idea to the test; namely, goats that, due to a naturally occurring nonsense mutation, lack PrPC . Teased nerve fiber preparation revealed a demyelinating pathology in goats without PrPC . Affected nerves were invaded by macrophages and T cells and displayed vacuolated fibers, shrunken axons, and onion bulbs. Peripheral nerve lipid composition was similar in young goats with or without PrPC , but markedly different between corresponding groups of adult goats, reflecting the progressive nature of the neuropathy. This is the first report of a subclinical demyelinating polyneuropathy caused by loss of PrPC function in a nontransgenic mammal.

Generalized myoclonic epilepsy with photosensitivity in juvenile dogs caused by a defective DIRAS family GTPase 1.

The clinical and electroencephalographic features of a canine generalized myoclonic epilepsy with photosensitivity and onset in young Rhodesian Ridgeback dogs (6 wk to 18 mo) are described. A fully penetrant recessive 4-bp deletion was identified in the DIRAS family GTPase 1 (DIRAS1) gene with an altered expression pattern of DIRAS1 protein in the affected brain. This neuronal DIRAS1 gene with a proposed role in cholinergic transmission provides not only a candidate for human myoclonic epilepsy but also insights into the disease etiology, while establishing a spontaneous model for future intervention studies and functional characterization.

The neuropathology of fatal encephalomyelitis in human Borna virus infection.

After many years of controversy, there is now recent and solid evidence that classical Borna disease virus 1 (BoDV-1) can infect humans. On the basis of six brain autopsies, we provide the first systematic overview on BoDV-1 tissue distribution and the lesion pattern in fatal BoDV-1-induced encephalitis. All brains revealed a non-purulent, lymphocytic sclerosing panencephalomyelitis with detection of BoDV-1-typical eosinophilic, spherical intranuclear Joest-Degen inclusion bodies. While the composition of histopathological changes was constant, the inflammatory distribution pattern varied interindividually, affecting predominantly the basal nuclei in two patients, hippocampus in one patient, whereas two patients showed a more diffuse distribution. By immunohistochemistry and RNA in situ hybridization, BoDV-1 was detected in all examined brain tissue samples. Furthermore, infection of the peripheral nervous system was observed. This study aims at raising awareness to human bornavirus encephalitis as differential diagnosis in lymphocytic sclerosing panencephalomyelitis. A higher attention to human BoDV-1 infection by health professionals may likely increase the detection of more cases and foster a clearer picture of the disease.

Cell and context-dependent sorting of neuropathy-associated protein NDRG1 - insights from canine tissues and primary Schwann cell cultures.

BACKGROUND: Mutations in the N-myc downstream-regulated gene 1 (NDRG1) can cause degenerative polyneuropathy in humans, dogs, and rodents. In humans, this motor and sensory neuropathy is known as Charcot-Marie-Tooth disease type 4D, and it is assumed that analogous canine diseases can be used as models for this disease. NDRG1 is also regarded as a metastasis-suppressor in several malignancies. The tissue distribution of NDRG1 has been described in humans and rodents, but this has not been studied in the dog. RESULTS: By immunolabeling and Western blotting, we present a detailed mapping of NDRG1 in dog tissues and primary canine Schwann cell cultures, with particular emphasis on peripheral nerves. High levels of phosphorylated NDRG1 appear in distinct subcellular localizations of the Schwann cells, suggesting signaling-driven rerouting of the protein. In a nerve from an Alaskan malamute homozygous for the disease-causing Gly98Val mutation in NDRG1, this signal was absent. Furthermore, NDRG1 is present in canine epithelial cells, predominantly in the cytosolic compartment, often with basolateral localization. Constitutive expression also occurs in mesenchymal cells, including developing spermatids that are transiently positive for NDRG1. In some cells, NDRG1 localize to centrosomes. CONCLUSIONS: Overall, canine NDRG1 shows a cell and context-dependent localization. Our data from peripheral nerves and primary Schwann cell cultures suggest that the subcellular localization of NDRG1 in Schwann cells is dynamically influenced by signaling events leading to reversible phosphorylation of the protein. We propose that disease-causing mutations in NDRG1 can disrupt signaling in myelinating Schwann cells, causing disturbance in myelin homeostasis and axonal-glial cross talk, thereby precipitating polyneuropathy.

Phenotype of macular corneal dystrophy in Labrador Retrievers: A multicenter study.

OBJECTIVE: To describe the phenotype of canine macular corneal dystrophy (MCD) including the clinical presentation, multimodal ocular imaging, histopathology, and ultrastructural analysis in ten Labrador Retrievers. PROCEDURE: Multicentered data collection. RESULTS: Labrador Retrievers affected by MCD were presented between the age of 4.5 and 6 years of age with a history of cloudy eyes and/or visual impairment. Findings on ophthalmic examination included a diffuse haze of the corneal stroma and multiple, well-demarcated, off-white to yellow-brown, punctate corneal opacities heterogeneous in size. Corneal vascularization developed in most dogs as the disease progressed. Disease progression was associated with increased density of the corneal haze as well as increased number and size of the focal opacities and dogs developed significant visual impairment. Spectral domain-optical coherence tomography revealed multifocal hyper-reflective regions within the stroma. In vivo confocal microscopy revealed marked alterations in reflectivity throughout the entire stroma. Normal keratocytes could not be identified in affected areas. Histopathology showed stromal collagen fibers separated by acidophilic granular material on hematoxylin and eosin stain. The material stained with periodic acid-Schiff and colloidal iron stain but not with Masson trichrome stain, confirming the accumulation of glycosaminoglycans. On electron microscopic ultrastructural examination, keratocytes presented with vacuolated rough endoplasmic reticulum and multiple electron dense cytoplasmic inclusions. In areas keratocytes appeared ruptured, with cell organelles and proteinaceous material grouped together between collagen fibers. CONCLUSION: MCD in Labrador Retrievers has similarities with the human counterpart of the condition and is an important differential diagnosis in dogs with corneal disease.

Utility of an immunocytochemical assay using aqueous humor in the diagnosis of feline infectious peritonitis.

OBJECTIVE: In cats suffering from feline infectious peritonitis (FIP) without effusion, antemortem diagnosis is challenging. Uveitis is common in these cats. It was the aim of this study to evaluate sensitivity and specificity of an immunocytochemical assay (ICC) in aqueous humor of cats suspected of having FIP. ANIMALS STUDIED: The study included 26 cats with immunohistochemically confirmed FIP and 12 control cats for which FIP was suspected due to similar clinical or laboratory changes, but which suffered from other diseases confirmed via histopathology. PROCEDURES: All aqueous humor samples were collected postmortem by paracentesis. ICC was carried out as avidin-biotin complex method. Sensitivity, specificity, and the overall accuracy including 95% confidence intervals (95% CI) were calculated. RESULTS: Immunocytochemistry was positive in 16 of 25 cats with FIP and 2 of 11 control cats (one cat with lymphoma, one with pulmonary adenocarcinoma). Aqueous humor samples of one cat with FIP and of one control cat were excluded from statistical analysis. Sensitivity was 64.0% (95% CI: 42.5-82.0); specificity 81.8% (95% CI: 48.2-97.7); and overall accuracy 69.4% (95% CI: 51.9-83.7). CONCLUSIONS: As false-positive results occurred and specificity is most important in the diagnosis of FIP, the diagnostic utility of ICC in aqueous humor is limited. Further studies are required to clarify the origin of false-positive ICC results.

Sensitivity and specificity of a real-time reverse transcriptase polymerase chain reaction detecting feline coronavirus mutations in effusion and serum/plasma of cats to diagnose feline infectious peritonitis.

BACKGROUND: Feline coronavirus (FCoV) exists as two pathotypes, and FCoV spike gene mutations are considered responsible for the pathotypic switch in feline infectious peritonitis (FIP) pathogenesis. The aim of this study was to evaluate sensitivity and specificity of a real-time reverse transcriptase polymerase chain reaction (RT-PCR) specifically designed to detect FCoV spike gene mutations at two nucleotide positions. It was hypothesized that this test would correctly discriminate feline infectious peritonitis virus (FIPV) and feline enteric coronavirus (FECV). METHODS: The study included 63 cats with signs consistent with FIP. FIP was confirmed in 38 cats. Twenty-five control cats were definitively diagnosed with a disease other than FIP. Effusion and/or serum/plasma samples were examined by real-time RT-PCR targeting the two FCoV spike gene fusion peptide mutations M1058 L and S1060A using an allelic discrimination approach. Sensitivity, specificity, negative and positive predictive values including 95% confidence intervals (95% CI) were calculated. RESULTS: FIPV was detected in the effusion of 25/59 cats, one of them being a control cat with chronic kidney disease. A mixed population of FIPV/FECV was detected in the effusion of 2/59 cats; all of them had FIP. RT-PCR was negative or the pathotype could not be determined in 34/59 effusion samples. In effusion, sensitivity was 68.6% (95% CI 50.7-83.2), specificity was 95.8% (95% CI 78.9-99.9). No serum/plasma samples were positive for FIPV. CONCLUSIONS: Although specificity of the test in effusions was high, one false positive result occurred. The use of serum/plasma cannot be recommended due to a low viral load in blood.

Cavalier King Charles Spaniels with Chiari-like malformation and Syringomyelia have increased variability of spatio-temporal gait characteristics.

BACKGROUND: Chiari-like malformation in the Cavalier King Charles Spaniel is a herniation of the cerebellum and brainstem into or through the foramen magnum. This condition predisposes to Syringomyelia; fluid filled syrinxes within the spinal cord. The resulting pathology in spinal cord and cerebellum create neuropathic pain and changes in gait. This study aims to quantify the changes in gait for Cavalier King Charles Spaniel with Chiari-like malformation and Syringomyelia. METHODS: We compared Cavalier King Charles Spaniel with Chiari-like malformation with (n = 9) and without (n = 8) Syringomyelia to Border Terriers (n = 8). Two video cameras and manual tracking was used to quantify gait parameters. RESULTS AND CONCLUSIONS: We found a significant increase in coefficient of variation for the spatio-temporal characteristics and ipsilateral distance between paws and a wider base of support in the thoracic limbs but not in the pelvic limbs for Cavalier King Charles Spaniels compared with the border terrier.

IMAGING DIAGNOSIS-CONCENTRIC PERIRADICULAR LIPOMA CAUSING LUMBAR NERVE ROOT COMPRESSION IN A DOG.

An 11-year-old, male neutered Jack Russell Terrier was presented with a nerve root signature of the right pelvic limb. Magnetic resonance imaging revealed a well demarcated, ovoid, extramedullary mass at the level of the L7 vertebral body. This showed, compared to normal spinal cord, hyperintense signal on T1- and T2-weighted images, which was suppressed on gradient echo short tau inversion recovery (GE-STIR) images. Additionally, the mass was characterized by a fat density on computed tomography images. Histopathology of the surgically excised mass was consistent with concentric periradicular lipoma, which has not been described in domestic animals yet.

Confirmation of a non-synonymous SNP in PNPLA8 as a candidate causal mutation for Weaver syndrome in Brown Swiss cattle.

BACKGROUND: Bovine progressive degenerative myeloencephalopathy (Weaver syndrome) is a neurodegenerative disorder in Brown Swiss cattle that is characterized by progressive hind leg weakness and ataxia, while sensorium and spinal reflexes remain unaffected. Although the causal mutation has not been identified yet, an indirect genetic test based on six microsatellite markers and consequent exclusion of Weaver carriers from breeding have led to the complete absence of new cases for over two decades. Evaluation of disease status by imputation of 41 diagnostic single nucleotide polymorphisms (SNPs) and a common haplotype published in 2013 identified several suspected carriers in the current breeding population, which suggests a higher frequency of the Weaver allele than anticipated. In order to prevent the reemergence of the disease, this study aimed at mapping the gene that underlies Weaver syndrome and thus at providing the basis for direct genetic testing and monitoring of today's Braunvieh/Brown Swiss herds. RESULTS: Combined linkage/linkage disequilibrium mapping on Bos taurus chromosome (BTA) 4 based on Illumina Bovine SNP50 genotypes of 43 Weaver-affected, 31 Weaver carrier and 86 Weaver-free animals resulted in a maximum likelihood ratio test statistic value at position 49,812,384 bp. The confidence interval (0.853 Mb) determined by the 2-LOD drop-off method was contained within a 1.72-Mb segment of extended homozygosity. Exploitation of whole-genome sequence data from two official Weaver carriers and 1145 other bulls that were sequenced in Run4 of the 1000 bull genomes project showed that only a non-synonymous SNP (rs800397662) within the PNPLA8 gene at position 49,878,773 bp was concordant with the Weaver carrier status. Targeted SNP genotyping confirmed this SNP as a candidate causal mutation for Weaver syndrome. Genotyping for the candidate causal mutation in a random sample of 2334 current Braunvieh animals suggested a frequency of the Weaver allele of 0.26 %. CONCLUSIONS: Through combined use of exhaustive sequencing data and SNP genotyping results, we were able to provide evidence that supports the non-synonymous mutation at position 49,878,773 bp as the most likely causal mutation for Weaver syndrome. Further studies are needed to uncover the exact mechanisms that underlie this syndrome.

Spinocerebellar ataxia in the Italian Spinone dog is associated with an intronic GAA repeat expansion in ITPR1.

Spinocerebellar ataxia in the Italian Spinone dog breed is characterised by a progressive gait abnormality that manifests from approximately 4 months of age. The disorder shows an autosomal recessive mode of inheritance, and affected individuals are usually euthanized by one year of age on welfare grounds due to an inability to ambulate. Using a homozygosity mapping technique with six cases and six controls, we mapped the disease locus to chromosome 20 of the canine genome. Linkage analysis across an extended pedigree confirmed the association, with microsatellite C20.374 achieving a maximal LOD score of 4.41. All five genes within the disease-associated interval were exon resequenced, although no exonic candidate mutations were identified. A targeted resequencing approach was therefore adopted to sequence the entire disease-associated interval. Analysis of the sequencing data revealed a GAA repeat expansion in intron 35 of ITPR1, which was homozygous in all cases and heterozygous in obligate carriers. Partial impairment of cerebellar ITPR1 expression in affected dogs was demonstrated by immunohistochemistry. Given the association of ITPR1 mutations with spinocerebellar ataxia (SCA) type 15 (also designated SCA16) in humans and that an intronic GAA repeat expansion has been shown to cause Friedreich ataxia, the repeat expansion is an excellent candidate for the cause of spinocerebellar ataxia in the Italian Spinone. This finding represents the first naturally occurring pathogenic intronic GAA repeat expansion in a non-human species and a novel mechanism for ITPR1 associated spinocerebellar ataxia.