Canine hereditary ataxia in old english sheepdogs and gordon setters is associated with a defect in the autophagy gene encoding RAB24

Clinical, imaging and histopathological characterization of a series of three cats with cerebellar cortical degeneration

BACKGROUND

Neurological inherited disorders are rare in domestic animals. Cerebellar cortical degeneration remains amongst the most common of these disorders. The condition is defined as the premature loss of fully differentiated cerebellar components due to genetic or metabolic defects. It has been studied in dogs and cats, and various genetic defects and diagnostic tests (including magnetic resonance imaging (MRI)) have been refined in these species. Cases in cats remain rare and mostly individual, and few diagnostic criteria, other than post-mortem exam, have been evaluated in reports with multiple cases. Here, we report three feline cases of cerebellar cortical degeneration with detailed clinical, diagnostic imaging and post-mortem findings.

CASE PRESENTATION

The three cases were directly (siblings, case #1 and #2) or indirectly related (same farm, case #3) and showed early-onset of the disease, with clinical signs including cerebellar ataxia and tremors. Brain MRI was highly suggestive of cerebellar cortical degeneration on all three cases. The relative cerebrospinal fluid (CSF) space, relative cerebellum size, brainstem: cerebellum area ratio, and cerebellum: total brain area ratio, were measured and compared to a control group of cats and reference cut-offs for dogs in the literature. For the relative cerebellum size and cerebellum: total brain area ratio, all affected cases had a lower value than the control group. For the relative CSF space and brainstem: cerebellum area ratio, the more affected cases (#2 and #3) had higher values than the control group, while the least affected case (#3) had values within the ranges of the control group, but a progression was visible over time. Post-mortem examination confirmed the diagnosis of cerebellar cortical degeneration, with marked to complete loss of Purkinje cells and associated granular layer depletion and proliferation of Bergmann glia. One case also had Wallerian-like degeneration in the spinal cord, suggestive of spinocerebellar degeneration.

CONCLUSION

Our report further supports a potential genetic component for the disease in cats. For the MRI examination, the relative cerebellum size and cerebellum: total brain area ratio seem promising, but further studies are needed to establish specific feline cut-offs. Post-mortem evaluation of the cerebellum remains the gold standard for the final diagnosis.

Clinicopathological and pedigree investigation of a novel spinocerebellar neurological disease in juvenile Quarter Horses in North America

BACKGROUND

In 2020, a novel neurologic disease was observed in juvenile Quarter Horses (QHs) in North America. It was unknown if this was an aberrant manifestation of another previously described neurological disorder in foals, such as equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM).

HYPOTHESIS/OBJECTIVES

To describe the clinical findings, outcomes, and postmortem changes with Equine Juvenile Spinocerebellar Ataxia (EJSCA), differentiate the disease from other similar neurological disorders, and determine a mode of inheritance.

ANIMALS

Twelve neurologically affected QH foals and the dams.

METHODS

Genomic DNA was isolated and pedigrees were manually constructed.

RESULTS

All foals (n = 12/12) had a history of acute onset of neurological deficits with no history of trauma. Neurological deficits were characterized by asymmetrical spinal ataxia, with pelvic limbs more severely affected than thoracic limbs. Clinicopathological abnormalities included high serum activity of gamma-glutamyl transferase and hyperglycemia. All foals became recumbent (median, 3 days: [0-18 days]), which necessitated humane euthanasia (n = 11/12, 92%; the remaining case was found dead). Histological evaluation at postmortem revealed dilated myelin sheaths and digestion chambers within the spinal cord, most prominently in the dorsal spinocerebellar tracts. Pedigree analysis revealed a likely autosomal recessive mode of inheritance.

CONCLUSIONS AND CLINICAL IMPORTANCE

EJSCA is a uniformly fatal, rapidly progressive, likely autosomal recessive neurological disease of QHs <1 month of age in North America that is etiologically distinct from other clinically similar neurological disorders. Once the causative variant for EJSCA is validated, carriers can be identified through genetic testing to inform breeding decisions.

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.

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.

The mediating role of gut microbiota in the associations of prenatal maternal combined exposure to lead and stress with neurodevelopmental deficits in young rats

Prenatal single and combined exposure to lead (Pb) and stress (Ps) impairs neurodevelopment. Prenatal single exposure to Pb or Ps affects the composition of intestinal microbiota, and bidirectional communication between gut microbiota and central nervous system has been well recognized. However, whether gut microbiota mediated the effects of prenatal Pb+Ps co-exposure on neurodevelopmental deficits remains unclear. This study established rat models with prenatal single and combined exposure to Ps and Pb. We investigated the effects of such prenatal single and combined exposure on hippocampal structures using morphological analyses, on learning/memory using the Morris-water-maze test, and on fecal microbiota using 16S rRNA sequencing. The mediating roles of gut microbiota were analyzed using the bootstrap method. The study found both single and combined exposure affected hippocampal ultra-structures and spatial learning/memory, and the most significant impairments were observed in the Pb+Ps group. Prenatal Pb+Ps co-exposure decreased fecal microbial alpha/beta-diversity. Significantly lower levels of B/F-ratio, class-Bacteroidia, order-Bacteroidales, and family-S24-7, and significantly higher levels of class-Bacilli, order-Lactobacillales, family-Lactobacillaceae, and genus-Lactobacillus were observed in the co-exposure group, compared with the controls. Increased relative abundances of genus-Helicobacter mediated the detrimental effect of prenatal Ps+Pb co-exposure on learning/memory [β (95%CI) for the total and indirect effects: - 10.70 (-19.19, -2.21) and - 4.65(-11.07, -1.85)], accounting for 43.47% of the total effect. As a result, increased relative abundances of genus-Lactobacillus alleviated the adverse effects of the co-exposure on learning/memory, and the alleviation effect accounted for 44.55% of the direct effect [β (95%CI) for the direct and indirect effects: - 0.28(-0.48, -0.08) and 0.13(0.01, 0.41)]. This study suggested that prenatal combined exposure to Pb and Ps induced more impairments in offspring gut microbiota and neurodevelopment than single exposure, and alterations in fecal microbiome may mediate the developmental neurotoxicity induced by such prenatal co-exposure.

Cerebellar Abiotrophy in Australian Working Kelpies Is Associated with Two Major Risk Loci

An autosomal recessive form of inherited cerebellar abiotrophy (CA) that is characterized by a degeneration of Purkinje and granule cells in the cerebellar cortex occurs in the Australian working kelpie dog breed. The clinical signs of CA include ataxia, head tremor, motor in-coordination, wide-based stance, and high-stepping gait. Investigation of clinical and pathological features indicated two closely related diseases with differences in age of onset. A genome-wide association study on 45 CA affected and 290 normal healthy Kelpies identified two significantly associated loci, one on CFA9 and a second on CFA20. Dogs homozygous for the risk haplotype on CFA20 (23 dogs) show clinical signs before ten weeks of age. Missense variants in the sixth exon of disruptor of telomeric silencing 1-like (DOT1Lp.R200Q) and in the only exon of Leucine Rich Repeat And Ig Domain Containing 3 (LINGO3p.R359C), both on CFA20, segregate with the associated risk marker which has incomplete penetrance (42%). Affected dogs homozygous for the risk haplotype on CFA9 have later onset ataxia. A missense variant in exon 5 of Vacuole Membrane Protein 1 (VMP1 p.P160Q) on CFA9 segregates as a fully penetrant Mendelian recessive with later-onset CA. Across mammals, the variety of causative loci so far identified as influencing cerebellar disorders reinforces the complexity of the pathways that contribute to cerebellar development and function, and to the pathophysiological mechanisms that may lead to cerebellar ataxia.

The spectrum of neurodevelopmental, neuromuscular and neurodegenerative disorders due to defective autophagy

Primary dysfunction of autophagy due to Mendelian defects affecting core components of the autophagy machinery or closely related proteins have recently emerged as an important cause of genetic disease. This novel group of human disorders may present throughout life and comprises severe early-onset neurodevelopmental and more common adult-onset neurodegenerative disorders. Early-onset (or congenital) disorders of autophagy often share a recognizable "clinical signature," including variable combinations of neurological, neuromuscular and multisystem manifestations. Structural CNS abnormalities, cerebellar involvement, spasticity and peripheral nerve pathology are prominent neurological features, indicating a specific vulnerability of certain neuronal populations to autophagic disturbance. A typically biphasic disease course of late-onset neurodegeneration occurring on the background of a neurodevelopmental disorder further supports a role of autophagy in both neuronal development and maintenance. Additionally, an associated myopathy has been characterized in several conditions. The differential diagnosis comprises a wide range of other multisystem disorders, including mitochondrial, glycogen and lysosomal storage disorders, as well as ciliopathies, glycosylation and vesicular trafficking defects. The clinical overlap between the congenital disorders of autophagy and these conditions reflects the multiple roles of the proteins and/or emerging molecular connections between the pathways implicated and suggests an exciting area for future research. Therapy development for congenital disorders of autophagy is still in its infancy but may result in the identification of molecules that target autophagy more specifically than currently available compounds. The close connection with adult-onset neurodegenerative disorders highlights the relevance of research into rare early-onset neurodevelopmental conditions for much more common, age-related human diseases.Abbreviations: AC: anterior commissure; AD: Alzheimer disease; ALR: autophagic lysosomal reformation; ALS: amyotrophic lateral sclerosis; AMBRA1: autophagy and beclin 1 regulator 1; AMPK: AMP-activated protein kinase; ASD: autism spectrum disorder; ATG: autophagy related; BIN1: bridging integrator 1; BPAN: beta-propeller protein associated neurodegeneration; CC: corpus callosum; CHMP2B: charged multivesicular body protein 2B; CHS: Chediak-Higashi syndrome; CMA: chaperone-mediated autophagy; CMT: Charcot-Marie-Tooth disease; CNM: centronuclear myopathy; CNS: central nervous system; DNM2: dynamin 2; DPR: dipeptide repeat protein; DVL3: disheveled segment polarity protein 3; EPG5: ectopic P-granules autophagy protein 5 homolog; ER: endoplasmic reticulum; ESCRT: homotypic fusion and protein sorting complex; FIG4: FIG4 phosphoinositide 5-phosphatase; FTD: frontotemporal dementia; GBA: glucocerebrosidase; GD: Gaucher disease; GRN: progranulin; GSD: glycogen storage disorder; HC: hippocampal commissure; HD: Huntington disease; HOPS: homotypic fusion and protein sorting complex; HSPP: hereditary spastic paraparesis; LAMP2A: lysosomal associated membrane protein 2A; MEAX: X-linked myopathy with excessive autophagy; mHTT: mutant huntingtin; MSS: Marinesco-Sjoegren syndrome; MTM1: myotubularin 1; MTOR: mechanistic target of rapamycin kinase; NBIA: neurodegeneration with brain iron accumulation; NCL: neuronal ceroid lipofuscinosis; NPC1: Niemann-Pick disease type 1; PD: Parkinson disease; PtdIns3P: phosphatidylinositol-3-phosphate; RAB3GAP1: RAB3 GTPase activating protein catalytic subunit 1; RAB3GAP2: RAB3 GTPase activating non-catalytic protein subunit 2; RB1: RB1-inducible coiled-coil protein 1; RHEB: ras homolog, mTORC1 binding; SCAR20: SNX14-related ataxia; SENDA: static encephalopathy of childhood with neurodegeneration in adulthood; SNX14: sorting nexin 14; SPG11: SPG11 vesicle trafficking associated, spatacsin; SQSTM1: sequestosome 1; TBC1D20: TBC1 domain family member 20; TECPR2: tectonin beta-propeller repeat containing 2; TSC1: TSC complex subunit 1; TSC2: TSC complex subunit 2; UBQLN2: ubiquilin 2; VCP: valosin-containing protein; VMA21: vacuolar ATPase assembly factor VMA21; WDFY3/ALFY: WD repeat and FYVE domain containing protein 3; WDR45: WD repeat domain 45; WDR47: WD repeat domain 47; WMS: Warburg Micro syndrome; XLMTM: X-linked myotubular myopathy; ZFYVE26: zinc finger FYVE-type containing 26.

Growth hormone rescue cerebellar degeneration in SCA3 transgenic mice

Spinocerebellar ataxia type 3 (SCA3) is a fatal neurodegenerative disease for which no identified effective treatment or prevention methods exist. However, low-dose growth hormone (GH) therapy, as a potential off-label use, may deter the progress of SCA3. SCA3 15Q and SCA3 84Q transgenic mice harboring a YAC transgene that expresses the human ATXN3 gene with a pathogenic expanded 15 CAG repeat and 84 CAG repeat motif, respectively, were recruited. SCA3 15Q transgenic mice were considered as the healthy control group, whereas low-dose GH- and PBS-treated SCA3 84Q transgenic mice were considered as the study and sham groups, respectively. The SCA3 84Q transgenic mice were administered intraperitoneal injections of GH or PBS weekly from the postnatal age of 9 months-18 months. After 9 months of GH treatment in the SCA3 84Q transgenic mice, all locomotor functions including rotarod test, behavior box analysis were restored. The GH-treated SCA3 84Q transgenic mice revealed more preserved Purkinje cells/cerebellar cortex and less ataxin-3 aggregation, DNA oxidative, cell apoptosis compared with the PBS-treated SCA3 84Q transgenic mice. GH therapy may be one of the potential off-labeled using in the alleviation of SCA3 progression.

Rab family of small GTPases: an updated view on their regulation and functions

The Rab family of small GTPases regulates intracellular membrane trafficking by orchestrating the biogenesis, transport, tethering, and fusion of membrane‐bound organelles and vesicles. Like other small GTPases, Rabs cycle between two states, an active (GTP‐loaded) state and an inactive (GDP‐loaded) state, and their cycling is catalyzed by guanine nucleotide exchange factors (GEFs) and GTPase‐activating proteins (GAPs). Because an active form of each Rab localizes on a specific organelle (or vesicle) and recruits various effector proteins to facilitate each step of membrane trafficking, knowing when and where Rabs are activated and what effectors Rabs recruit is crucial to understand their functions. Since the discovery of Rabs, they have been regarded as one of the central hubs for membrane trafficking, and numerous biochemical and genetic studies have revealed the mechanisms of Rab functions in recent years. The results of these studies have included the identification and characterization of novel GEFs, GAPs, and effectors, as well as post‐translational modifications, for example, phosphorylation, of Rabs. Rab functions beyond the simple effector‐recruiting model are also emerging. Furthermore, the recently developed CRISPR/Cas technology has enabled acceleration of knockout analyses in both animals and cultured cells and revealed previously unknown physiological roles of many Rabs. In this review article, we provide the most up‐to‐date and comprehensive lists of GEFs, GAPs, effectors, and knockout phenotypes of mammalian Rabs and discuss recent findings in regard to their regulation and functions.

Genome-wide association studies and genetic testing: understanding the science, success, and future of a rapidly developing field

Dog owners are increasingly interested in using commercially available testing panels to learn about the genetics of their pets, both to identify breed ancestry and to screen for specific genetic diseases. Helping owners interpret and understand results from genetic screening panels is becoming an important issue facing veterinarians. The objective of this review article is to introduce basic concepts behind genetic studies and current genetic screening tests while highlighting their value in veterinary medicine. The potential uses and limitations of commercially available genetic testing panels as screening tests are discussed, including appropriate cautions regarding the interpretation of results. Future directions, particularly with regard to the study of common complex genetic diseases, are also described.

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.

Autophagy-Related Gene 7 Polymorphisms and Cerebral Palsy in Chinese Infants

Cerebral palsy (CP) is a group of non-progressive motor impairment syndromes that are secondary to brain injury in the early stages of brain development. Numerous etiologies and risk factors of CP have been reported, and genetic contributions have recently been identified. Autophagy has an important role in brain development and pathological process, and autophagy-related gene 7 (ATG7) is essential for autophagosome biogenesis. The purpose of this study was to investigate the genetic association between ATG7 gene single nucleotide polymorphisms (SNPs) and CP in Han Chinese children. Six SNPs (rs346078, rs1470612, rs11706903, rs2606750, rs2594972, and rs4684787) were genotyped in 715 CP patients and 658 healthy controls using the MassArray platform. Plasma ATG7 protein was determined in 73 CP patients and 79 healthy controls. The differences in the allele and genotype frequencies of the rs1470612 and rs2594972 SNPs were determined between the CP patients and controls (p _allele = 0.02 and 0.0004, p _genotype = 0.044 and 0.0012, respectively). Subgroup analysis revealed a more significant association of rs1470612 (p _allele = 0.004, p _genotype = 0.0036) and rs2594972 (p _allele = 0.0004, p _genotype < 0.0001) with male CP, and more significant differences in allele and genotype frequencies were also noticed between CP patients with spastic diplegia and controls for rs1470612 (p _allele = 0.0024, p _genotype = 0.008) and rs2594972 (p _allele < 0.0001, p _genotype = 0.006). The plasma ATG7 level was higher in CP patients compared to the controls (10.58 ± 0.85 vs. 8.18 ± 0.64 pg/mL, p = 0.024). The luciferase reporter gene assay showed that the T allele of rs2594972 SNP could significantly increase transcriptional activity of the ATG7 promoter compared to the C allele (p = 0.009). These findings suggest that an association exists between genetic variants of ATG7 and susceptibility to CP, which provides novel evidence for the role of ATG7 in CP and contributes to our understanding of the molecular mechanisms of this neurodevelopmental disorder.

Genetic Pathways of Aging and Their Relevance in the Dog as a Natural Model of Human Aging

Aging research has experienced a burst of scientific efforts in the last decades as the growing ratio of elderly people has begun to pose an increased burden on the healthcare and pension systems of developed countries. Although many breakthroughs have been reported in understanding the cellular mechanisms of aging, the intrinsic and extrinsic factors that contribute to senescence on higher biological levels are still barely understood. The dog, Canis familiaris, has already served as a valuable model of human physiology and disease. The possible role the dog could play in aging research is still an open question, although utilization of dogs may hold great promises as they naturally develop age-related cognitive decline, with behavioral and histological characteristics very similar to those of humans. In this regard, family dogs may possess unmatched potentials as models for investigations on the complex interactions between environmental, behavioral, and genetic factors that determine the course of aging. In this review, we summarize the known genetic pathways in aging and their relevance in dogs, putting emphasis on the yet barely described nature of certain aging pathways in canines. Reasons for highlighting the dog as a future aging and gerontology model are also discussed, ranging from its unique evolutionary path shared with humans, its social skills, and the fact that family dogs live together with their owners, and are being exposed to the same environmental effects.

Hereditary ataxia in four related Norwegian Buhunds

CASE DESCRIPTION Two 12-week-old Norwegian Buhunds from a litter of 5 were evaluated because of slowly progressive cerebellar ataxia and fine head tremors. Two other females from the same pedigree had been previously evaluated for similar signs. CLINICAL FINDINGS Findings of general physical examination, CBC, and serum biochemical analysis were unremarkable for all affected puppies. Brain MRI and CSF analysis, including PCR assays for detection of Toxoplasma gondii, Neospora caninum, and canine distemper virus, were performed for 3 dogs, yielding unremarkable results. Urinary organic acid screening, enzyme analysis of fibroblasts cultured from skin biopsy specimens, and brainstem auditory-evoked response testing were performed for 2 puppies, and results were also unremarkable. TREATMENT AND OUTCOME The affected puppies were euthanized at the breeder's request, and their brains and spinal cords were submitted for histologic examination. Histopathologic findings included a markedly reduced expression of calbindin D28K and inositol triphosphate receptor 1 by Purkinje cells, with only mild signs of neuronal degeneration. Results of pedigree analysis suggested an autosomal recessive mode of inheritance. Candidate-gene analysis via mRNA sequencing for 2 of the affected puppies revealed no genetic variants that could be causally associated with the observed abnormalities. CLINICAL RELEVANCE Findings for the dogs of this report suggested the existence of a hereditary form of ataxia in Norwegian Buhunds with histologic characteristics suggestive of Purkinje cell dysfunction. The presence of hereditary ataxia in this breed must be considered both in clinical settings and for breeding strategies.

Roles for RAB24 in autophagy and disease

Autophagy is an evolutionarily conserved degradation pathway for cells to maintain homeostasis, produce energy, degrade misfolded proteins and damaged organelles, and fight against intracellular pathogens. The process of autophagy entails the isolation of cytoplasmic cargo into double membrane bound autophagosomes that undergo maturation by fusion with endosomes and lysosomes to obtain degradation capacity. RAB proteins regulate intracellular vesicle trafficking events including autophagy. RAB24 is an atypical RAB protein that is required for the clearance of late autophagic vacuoles under basal conditions. RAB24 has also been connected to several diseases including ataxia, cancer and tuberculosis. This review gives a short summary on autophagy and RAB proteins, and an overview on the current knowledge on the roles of RAB24 in autophagy and disease.

Consequences of Rab GTPase dysfunction in genetic or acquired human diseases

Rab GTPases are important regulators of intracellular membrane trafficking in eukaryotes. Both activating and inactivating mutations in Rab genes have been identified and implicated in human diseases ranging from neurological disorders to cancer. In addition, altered Rab expression is often associated with disease prognosis. As such, the study of diseases associated with Rabs or Rab-interacting proteins has shed light on the important role of intracellular membrane trafficking in disease etiology. In this review, we cover recent advances in the field with an emphasis on cellular mechanisms.

Consequences of Rab GTPase dysfunction in genetic or acquired human diseases

Rab GTPases are important regulators of intracellular membrane trafficking in eukaryotes. Both activating and inactivating mutations in Rab genes have been identified and implicated in human diseases ranging from neurological disorders to cancer. In addition, altered Rab expression is often associated with disease prognosis. As such, the study of diseases associated with Rabs or Rab-interacting proteins has shed light on the important role of intracellular membrane trafficking in disease etiology. In this review, we cover recent advances in the field with an emphasis on cellular mechanisms.

Familial episodic ataxia in lambs is potentially associated with a mutation in the fibroblast growth factor 14 (FGF14) gene

Familial episodic ataxia of lambs is a congenital transient autosomal dominant disorder of newborn lambs, with varying expressivity. Affected lambs show episodes of an asymmetric ataxic gait, base-wide extensor hypertonia of the thoracic limbs and flexor hypertonia of the pelvic limbs. The aim of the study was to determine the genetic variant causing familial episodic ataxia in lambs. Using whole genome sequencing of two half-sib affected lambs, their sire, and their two normal dams, a heterozygous C>T transition at OAR10:77593415 (Oar_v3.1) in exon 1 of the fibroblast growth factor 14 (FGF14) gene (c.46C>T) was identified. The c.46C>T transition resulted in a premature stop codon at position 16 of the 247 amino acid FGF14 protein (p.Q16*). PCR and Sanger sequencing was used to genotype an additional 20 clinically affected animals, demonstrating all lambs carried the c.46C>T variant but 1 clinically more severely affected inbred lamb was homozygous (TT). A further 11 unrelated normal ewes were positionally sequenced, none of which had the variant, while in 18 lambs of unknown status born over 2 years of breeding trials six lambs were found to have the c.46C>T variant, likely clinically unidentified heterozygotes due to the variable expressivity, while 12 did not. In conclusion, familial episodic ataxia of lambs is potentially associated with a c.46C>T variant in the FGF14 gene. Further research is required into the mechanism behind the apparent recovery of lambs.

Transplantation of Human Neural Progenitor Cells Reveals Structural and Functional Improvements in the Spastic Han-Wistar Rat Model of Ataxia

The use of regenerative medicine to treat nervous system disorders like ataxia has been proposed to either replace or support degenerating neurons. In this study, we assessed the ability of human neural progenitor cells (hNPCs) to repair and restore the function of dying neurons within the spastic Han-Wistar rat (sHW), a model of ataxia. The sHW rat suffers from neurodegeneration of specific neurons, including cerebellar Purkinje cells and hippocampal CA3 pyramidal cells leading to the observed symptoms of forelimb tremor, hind-leg rigidity, gait abnormality, motor incoordination, and a shortened life span. To alleviate the symptoms of neurodegeneration and to replace or augment dying neurons, neuronal human progenitor cells were implanted into the sHW rats. At 30 d of age, male sHW mutant rats underwent subcutaneous implantation of an Alzet osmotic pump that infused cyclosporine (15 mg/kg/d) used to suppress the rat's immune system. At 40 d, sHW rats received bilateral injections (500,000 cells in 5 µL media) of live hNPCs, dead hNPCs, live human embryonic kidney cells, or growth media either into the cerebellar cortex or into the hippocampus. To monitor results, motor activity scores (open-field testing) and weights of the animals were recorded weekly. The sHW rats that received hNPC transplantation into the cerebellum, at 60 d of age, displayed significantly higher motor activity scores and sustained greater weights and longevities than control-treated sHW rats or any hippocampal treatment group. In addition, cerebellar histology revealed that the transplanted hNPCs displayed signs of migration and signs of neuronal development in the degenerated Purkinje cell layer. This study revealed that implanted human progenitor cells reduced the ataxic symptoms in the sHW rat, identifying a future clinical use of these progenitor cells against ataxia and associated neurodegenerative diseases.

Networks Underpinning Symbiosis Revealed Through Cross-Species eQTL Mapping

Organisms engage in extensive cross-species molecular dialog, yet the underlying molecular actors are known for only a few interactions. Many techniques have been designed to uncover genes involved in signaling between organisms. Typically, these focus on only one of the partners. We developed an expression quantitative trait locus (eQTL) mapping-based approach to identify cause-and-effect relationships between genes from two partners engaged in an interspecific interaction. We demonstrated the approach by assaying expression of 98 isogenic plants (Medicago truncatula), each inoculated with a genetically distinct line of the diploid parasitic nematode Meloidogyne hapla With this design, systematic differences in gene expression across host plants could be mapped to genetic polymorphisms of their infecting parasites. The effects of parasite genotypes on plant gene expression were often substantial, with up to 90-fold (P = 3.2 × 10-52) changes in expression levels caused by individual parasite loci. Mapped loci included a number of pleiotropic sites, including one 87-kb parasite locus that modulated expression of >60 host genes. The 213 host genes identified were substantially enriched for transcription factors. We distilled higher-order connections between polymorphisms and genes from both species via network inference. To replicate our results and test whether effects were conserved across a broader host range, we performed a confirmatory experiment using M. hapla-infected tomato. This revealed that homologous genes were similarly affected. Finally, to validate the broader utility of cross-species eQTL mapping, we applied the strategy to data from a Salmonella infection study, successfully identifying polymorphisms in the human genome affecting bacterial expression.

Basal Autophagy Is Altered in Lagotto Romagnolo Dogs with an ATG4D Mutation

A missense variant in the autophagy-related ATG4D-gene has been associated with a progressive degenerative neurological disease in Lagotto Romagnolo (LR) dogs. In addition to neural lesions, affected dogs show an extraneural histopathological phenotype characterized by severe cytoplasmic vacuolization, a finding not previously linked with disturbed autophagy in animals. Here we aimed at testing the hypothesis that autophagy is altered in the affected dogs, at reporting the histopathology of extraneural tissues and at excluding lysosomal storage diseases. Basal and starvation-induced autophagy were monitored by Western blotting and immunofluorescence of microtubule associated protein 1A/B light chain3 (LC3) in fibroblasts from 2 affected dogs. The extraneural findings of 9 euthanized LRs and skin biopsies from 4 living affected LRs were examined by light microscopy, electron microscopy, and immunohistochemistry (IHC), using antibodies against autophagosomal membranes (LC3), autophagic cargo (p62), and lysosomal membranes (LAMP2). Biochemical screening of urine and fibroblasts of 2 affected dogs was performed. Under basal conditions, the affected fibroblasts contained significantly more LC3-II and LC3-positive vesicles than did the controls. Morphologically, several cells, including serous secretory epithelium, endothelial cells, pericytes, plasma cells, and macrophages, contained cytoplasmic vacuoles with an ultrastructure resembling enlarged amphisomes, endosomes, or multivesicular bodies. IHC showed strong membranous LAMP2 positivity only in sweat glands. The results show that basal but not induced autophagy is altered in affected fibroblasts. The ultrastructure of affected cells is compatible with altered autophagic and endo-lysosomal vesicular traffic. The findings in this spontaneous disease provide insight into possible tissue-specific roles of basal autophagy.

Genetics of Hereditary Ataxia in Scottish Terriers

BACKGROUND

Scottish Terriers have a high incidence of juvenile onset hereditary ataxia primarily affecting the Purkinje neuron of the cerebellar cortex and causing slowly progressive cerebellar dysfunction.

OBJECTIVE

To identify chromosomal regions associated with hereditary ataxia in Scottish Terriers.

ANIMALS

One hundred and fifty-three Scottish Terriers were recruited through the Scottish Terrier Club of America.

MATERIALS AND METHODS

Prospective study. Dogs were classified as affected if they had slowly progressive cerebellar signs. When possible, magnetic resonance imaging and histopathological evaluation of the brain were completed as diagnostic aids. To identify genomic regions connected with the disease, genome-wide mapping was performed using both linkage- and association-based approaches. Pedigree evaluation and homozygosity mapping were also performed to examine mode of inheritance and to investigate the region of interest, respectively.

RESULTS

Linkage and genome-wide association studies in a cohort of Scottish Terriers both identified a region on CFA X strongly associated with the disease trait. Homozygosity mapping revealed a 4 Mb region of interest. Pedigree evaluation failed to identify the possible mode of inheritance due to the lack of complete litter information.

CONCLUSION AND CLINICAL IMPORTANCE

This finding suggests that further genetic investigation of the potential region of interest on CFA X should be considered in order to identify the causal mutation as well as develop a genetic test to eliminate the disease from this breed.

Roles for RAB24 in autophagy and disease

Autophagy is an evolutionarily conserved degradation pathway for cells to maintain homeostasis, produce energy, degrade misfolded proteins and damaged organelles, and fight against intracellular pathogens. The process of autophagy entails the isolation of cytoplasmic cargo into double membrane bound autophagosomes that undergo maturation by fusion with endosomes and lysosomes to obtain degradation capacity. RAB proteins regulate intracellular vesicle trafficking events including autophagy. RAB24 is an atypical RAB protein that is required for the clearance of late autophagic vacuoles under basal conditions. RAB24 has also been connected to several diseases including ataxia, cancer and tuberculosis. This review gives a short summary on autophagy and RAB proteins, and an overview on the current knowledge on the roles of RAB24 in autophagy and disease.

Rab24 interacts with the Rab7/Rab interacting lysosomal protein complex to regulate endosomal degradation

Endocytosis is a multistep process engaged in extracellular molecules internalization. Several proteins including the Rab GTPases family coordinate the endocytic pathway. The small GTPase Rab7 is present in late endosome (LE) compartments being a marker of endosome maturation. The Rab interacting lysosomal protein (RILP) is a downstream effector of Rab7 that recruits the functional dynein/dynactin motor complex to late compartments. In the present study, we have found Rab24 as a component of the endosome-lysosome degradative pathway. Rab24 is an atypical protein of the Rab GTPase family, which has been attributed a function in vesicle trafficking and autophagosome maturation. Using a model of transiently expressed proteins in K562 cells, we found that Rab24 co-localizes in vesicular structures labeled with Rab7 and LAMP1. Moreover, using a dominant negative mutant of Rab24 or a siRNA-Rab24 we showed that the distribution of Rab7 in vesicles depends on a functional Rab24 to allow DQ-BSA protein degradation. Additionally, by immunoprecipitation and pull down assays, we have demonstrated that Rab24 interacts with Rab7 and RILP. Interestingly, overexpression of the Vps41 subunit from the homotypic fusion and protein-sorting (HOPS) complex hampered the co-localization of Rab24 with RILP or with the lysosomal GTPase Arl8b, suggesting that Vps41 would affect the Rab24/RILP association. In summary, our data strongly support the hypothesis that Rab24 forms a complex with Rab7 and RILP on the membranes of late compartments. Our work provides new insights into the molecular function of Rab24 in the last steps of the endosomal degradative pathway.

RAB24 facilitates clearance of autophagic compartments during basal conditions

RAB24 belongs to a family of small GTPases and has been implicated to function in autophagy. Here we confirm the intracellular localization of RAB24 to autophagic vacuoles with immuno electron microscopy and cell fractionation, and show that prenylation and guanine nucleotide binding are necessary for the targeting of RAB24 to autophagic compartments. Further, we show that RAB24 plays a role in the maturation and/or clearance of autophagic compartments under nutrient-rich conditions, but not during short amino acid starvation. Quantitative electron microscopy shows an increase in the numbers of late autophagic compartments in cells silenced for RAB24, and mRFP-GFP-LC3 probe and autophagy flux experiments indicate that this is due to a hindrance in their clearance. Formation of autophagosomes is shown to be unaffected by RAB24-silencing with siRNA. A defect in aggregate clearance in the absence of RAB24 is also shown in cells forming polyglutamine aggregates. This study places RAB24 function in the termination of the autophagic process under nutrient-rich conditions.

Genome sequencing reveals a splice donor site mutation in the SNX14 gene associated with a novel cerebellar cortical degeneration in the Hungarian Vizsla dog breed

Background

Cerebellar cortical degeneration (CCD) is an increasingly recognised neurodegenerative disease process affecting many dog breeds. Typical presentation consists of a progressive cerebellar ataxia, with a variable age at onset and rate of progression between different breeds. Cerebellar histopathological findings typically consist of primary Purkinje neuronal degeneration and loss, with variable secondary depletion of the granular and molecular cell layers. Causative genes have been identified associated with CCD in several breeds, allowing screening for selective breeding to reduce the prevalence of these conditions. There have been no previous reports of CCD in Hungarian Vizslas.

Results

Two full-sibling Hungarian Vizsla puppies from a litter of nine presented with a history of progressive ataxia, starting around three months of age. Clinical signs included marked hypermetric and dysmetric ataxia, truncal sway, intention tremors and absent menace responses, with positional horizontal nystagmus in one dog. Routine diagnostic investigations were unremarkable, and magnetic resonance imaging performed in one dog revealed mild craniodorsal cerebellar sulci widening, supportive of cerebellar atrophy. Owners of both dogs elected for euthanasia shortly after the onset of signs. Histopathological examination revealed primary Purkinje neuron loss consistent with CCD. Whole genome sequencing was used to successfully identify a disease-associated splice donor site variant in the sorting nexin 14 gene (SNX14) as a strong causative candidate. An altered SNX14 splicing pattern for a CCD case was demonstrated by RNA analysis, and no SNX14 protein could be detected in CCD case cerebellum by western blotting. SNX14 is involved in maintaining normal neuronal excitability and synaptic transmission, and a mutation has recently been found to cause autosomal recessive cerebellar ataxia and intellectual disability syndrome in humans. Genetic screening of 133 unaffected Hungarian Vizslas revealed the presence of three heterozygotes, supporting the presence of carriers in the wider population.

Conclusions

This is the first report of CCD in Hungarian Vizsla dogs and identifies a highly associated splice donor site mutation in SNX14, with an autosomal recessive mode of inheritance suspected.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0433-y) contains supplementary material, which is available to authorized users.

The canine era: the rise of a biomedical model

Since the annotation of its genome a decade ago, the dog has proven to be an excellent model for the study of inherited diseases. A large variety of spontaneous simple and complex phenotypes occur in dogs, providing physiologically relevant models to corresponding human conditions. In addition, gene discovery is facilitated in clinically less heterogeneous purebred dogs with closed population structures because smaller study cohorts and fewer markers are often sufficient to expose causal variants. Here, we review the development of genomic resources from microsatellites to whole-genome sequencing and give examples of successful findings that have followed the technological progress. The increasing amount of whole-genome sequence data warrants better functional annotation of the canine genome to more effectively utilise this unique model to understand genetic contributions in morphological, behavioural and other complex traits.

Emerging nexus between RAB GTPases, autophagy and neurodegeneration

The RAB class of small GTPases includes the major regulators of intracellular communication, which are involved in vesicle generation through fusion and fission, and vesicular trafficking. RAB proteins also play an imperative role in neuronal maintenance and survival. Recent studies in the field of neurodegeneration have also highlighted the process of autophagy as being essential for neuronal maintenance. Here we review the emerging roles of RAB proteins in regulating macroautophagy and its impact in the context of neurodegenerative diseases.

From caveman companion to medical innovator: genomic insights into the origin and evolution of domestic dogs

The phenotypic and behavioral diversity of the domestic dog has yet to be matched by any other mammalian species. In their current form, which comprises more than 350 populations known as breeds, there is a size range of two orders of magnitude and morphological features reminiscent of not only different species but also different phylogenetic families. The range of both appearance and behavior found in the dog is the product of millennia of human interference, and though humans created the diversity it remains a point of fascination to both lay and scientific communities. In this review we summarize the current understanding of the history of dog domestication based on molecular data. We will examine the ways that canine genetic and genomic studies have evolved and look at examples of dog genetics in the light of human disease.

A missense change in the ATG4D gene links aberrant autophagy to a neurodegenerative vacuolar storage disease

Inherited neurodegenerative disorders are debilitating diseases that occur across different species. We have performed clinical, pathological and genetic studies to characterize a novel canine neurodegenerative disease present in the Lagotto Romagnolo dog breed. Affected dogs suffer from progressive cerebellar ataxia, sometimes accompanied by episodic nystagmus and behavioral changes. Histological examination revealed unique pathological changes, including profound neuronal cytoplasmic vacuolization in the nervous system, as well as spheroid formation and cytoplasmic aggregation of vacuoles in secretory epithelial tissues and mesenchymal cells. Genetic analyses uncovered a missense change, c.1288G>A; p.A430T, in the autophagy-related ATG4D gene on canine chromosome 20 with a highly significant disease association (p = 3.8 x 10^-136) in a cohort of more than 2300 Lagotto Romagnolo dogs. ATG4D encodes a poorly characterized cysteine protease belonging to the macroautophagy pathway. Accordingly, our histological analyses indicated altered autophagic flux in affected tissues. The knockdown of the zebrafish homologue atg4da resulted in a widespread developmental disturbance and neurodegeneration in the central nervous system. Our study describes a previously unknown canine neurological disease with particular pathological features and implicates the ATG4D protein as an important autophagy mediator in neuronal homeostasis. The canine phenotype serves as a model to delineate the disease-causing pathological mechanism(s) and ATG4D function, and can also be used to explore treatment options. Furthermore, our results reveal a novel candidate gene for human neurodegeneration and enable the development of a genetic test for veterinary diagnostic and breeding purposes.

Neurodegenerative disorders affect millions of people worldwide. We describe a novel neurodegenerative disease in a canine model, characterized by progressive cerebellar ataxia and cellular vacuolization. Our genetic analyses identified a single nucleotide change in the autophagy-related ATG4D gene in affected dogs. The ATG4D gene has not been linked to inherited diseases before. The autophagy-lysosome pathway plays an important role in degrading and recycling different cellular components. Disturbed autophagy has been reported in several different diseases but mutations in core autophagy components are rare. Histological analyses of affected canine brain tissues revealed altered autophagic flux, and a knockdown of the gene in the zebrafish model caused marked neurodevelopmental alterations and neurodegeneration. Our findings identify a new disease-causing pathway and implicate the ATG4D protease as an important mediator for neuronal homeostasis. Furthermore, our study establishes a large animal model to investigate the role of ATG4D in autophagy and to test possible treatment options.

Canine hereditary ataxia

The hereditary ataxias are a group of neurodegenerative diseases that cause a progressive (or episodic) cerebellar ataxia. A large number of different disorders have been described in different breeds of purebred dog, and in some instances, more than one disorder occurs in a single breed, creating a confusing clinical picture. The mutations associated with these disorders are being described at a rapid rate, potentially changing our ability to prevent, diagnose, and treat affected dogs. A breed-related neurodegenerative process should be suspected in any pure bred dog with slowly progressive, symmetric signs of ataxia.