Australian Cattle Dogs with Neuronal Ceroid Lipofuscinosis are Homozygous for a CLN5 Nonsense Mutation Previously Identified in Border Collies

Neuronal Ceroid Lipofuscinosis in a Mixed-Breed Dog with a Splice Site Variant in CLN6

A 23-month-old neutered male dog of unknown ancestry presented with a history of progressive neurological signs that included anxiety, cognitive impairment, tremors, seizure activity, ataxia, and pronounced visual impairment. The clinical signs were accompanied by global brain atrophy. Due to progression in the severity of disease signs, the dog was euthanized at 26 months of age. An examination of the tissues collected at necropsy revealed dramatic intracellular accumulations of autofluorescent inclusions in the brain, retina, and cardiac muscle. The inclusions were immunopositive for subunit c of mitochondrial ATP synthase, and their ultrastructural appearances were similar to those of lysosomal storage bodies that accumulate in some neuronal ceroid lipofuscinosis (NCL) diseases. The dog also exhibited widespread neuroinflammation. Based on these findings, the dog was deemed likely to have suffered from a form of NCL. A whole genome sequence analysis of the proband's DNA revealed a homozygous C to T substitution that altered the intron 3-exon 4 splice site of CLN6. Other mutations in CLN6 cause NCL diseases in humans and animals, including dogs. The CLN6 protein was undetectable with immunolabeling in the tissues of the proband. Based on the clinical history, fluorescence and electron-microscopy, immunohistochemistry, and molecular genetic findings, the disorder in this dog was classified as an NCL resulting from the absence of the CLN6 protein. Screening the dog's genome for a panel of breed-specific polymorphisms indicated that its ancestry included numerous breeds, with no single breed predominating. This suggests that the CLN6 disease variant is likely to be present in other mixed-breed dogs and at least some ancestral breeds, although it is likely to be rare since other cases have not been reported to date.

Beta-mannosidosis in a domestic cat associated with a missense variant in MANBA

A 6-month-old cat of unknown ancestry presented for a neurologic evaluation due to progressive motor impairment. Complete physical and neurologic examinations suggested the disorder was likely to be hereditary, although the signs were not consistent with any previously described inherited disorders in cats. Due to the progression of disease signs including severely impaired motor function and cognitive decline, the cat was euthanized at approximately 10.5 months of age. Whole genome sequence analysis identified a homozygous missense variant c.2506G > A in MANBA that predicts a p.Gly836Arg alteration in the encoded lysosomal enzyme β -mannosidase. This variant was not present in the whole genome or whole exome sequences of any of the 424 cats represented in the 99 Lives Cat Genome dataset. β -Mannosidase enzyme activity was undetectable in brain tissue homogenates from the affected cat, whereas α-mannosidase enzyme activities were elevated compared to an unaffected cat. Postmortem examination of brain and retinal tissues revealed massive accumulations of vacuolar inclusions in most cells, similar to those reported in animals of other species with hereditary β -mannosidosis. Based on these findings, the cat likely suffered from β -mannosidosis due to the abolition of β -mannosidase activity associated with the p.Gly836Arg amino acid substitution. p.Gly836 is located in the C-terminal region of the protein and was not previously known to be involved in modulating enzyme activity. In addition to the vacuolar inclusions, some cells in the brain of the affected cat contained inclusions that exhibited lipofuscin-like autofluorescence. Electron microscopic examinations suggested these inclusions formed via an autophagy-like process.

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 Homozygous MAN2B1 Missense Mutation in a Doberman Pinscher Dog with Neurodegeneration, Cytoplasmic Vacuoles, Autofluorescent Storage Granules, and an α-Mannosidase Deficiency

A 7-month-old Doberman Pinscher dog presented with progressive neurological signs and brain atrophy suggestive of a hereditary neurodegenerative disorder. The dog was euthanized due to the progression of disease signs. Microscopic examination of tissues collected at the time of euthanasia revealed massive accumulations of vacuolar inclusions in cells throughout the central nervous system, suggestive of a lysosomal storage disorder. A whole genome sequence generated with DNA from the affected dog contained a likely causal, homozygous missense variant in MAN2B1 that predicted an Asp104Gly amino acid substitution that was unique among whole genome sequences from over 4000 dogs. A lack of detectable α-mannosidase enzyme activity confirmed a diagnosis of a-mannosidosis. In addition to the vacuolar inclusions characteristic of α-mannosidosis, the dog exhibited accumulations of autofluorescent intracellular inclusions in some of the same tissues. The autofluorescence was similar to that which occurs in a group of lysosomal storage disorders called neuronal ceroid lipofuscinoses (NCLs). As in many of the NCLs, some of the storage bodies immunostained strongly for mitochondrial ATP synthase subunit c protein. This protein is not a substrate for α-mannosidase, so its accumulation and the development of storage body autofluorescence were likely due to a generalized impairment of lysosomal function secondary to the accumulation of α-mannosidase substrates. Thus, it appears that storage body autofluorescence and subunit c accumulation are not unique to the NCLs. Consistent with generalized lysosomal impairment, the affected dog exhibited accumulations of intracellular inclusions with varied and complex ultrastructural features characteristic of autophagolysosomes. Impaired autophagic flux may be a general feature of this class of disorders that contributes to disease pathology and could be a target for therapeutic intervention. In addition to storage body accumulation, glial activation indicative of neuroinflammation was observed in the brain and spinal cord of the proband.

Characterization of neuropathology in ovine CLN5 and CLN6 neuronal ceroid lipofuscinoses (Batten disease)

Sheep with naturally occurring CLN5 and CLN6 forms of neuronal ceroid lipofuscinoses (Batten disease) share the key clinical features of the human disease and represent an ideal model system in which the clinical efficacy of gene therapies is developed and test. However, it was first important to characterize the neuropathological changes that occur with disease progression in affected sheep. This study compared neurodegeneration, neuroinflammation, and lysosomal storage accumulation in CLN5 affected Borderdale, CLN6 affected South Hampshire, and Merino sheep brains from birth to end-stage disease at ≤24 months of age. Despite very different gene products, mutations, and subcellular localizations, the pathogenic cascade was remarkably similar for all three disease models. Glial activation was present at birth in affected sheep and preceded neuronal loss, with both spreading from the visual and parieto-occipital cortices most prominently associated with clinical symptoms to the entire cortical mantle by end-stage disease. In contrast, the subcortical regions were less involved, yet lysosomal storage followed a near-linear increase across the diseased sheep brain with age. Correlation of these neuropathological changes with published clinical data identified three potential therapeutic windows in affected sheep-presymptomatic (3 months), early symptomatic (6 months), and a later symptomatic disease stage (9 months of age)-beyond which the extensive depletion of neurons was likely to diminish any chance of therapeutic benefit. This comprehensive natural history of the neuropathological changes in ovine CLN5 and CLN6 disease will be integral in determining what impact treatment has at each of these disease stages.

The number of mitochondrial DNA mutations as a genetic feature for hair cycle arrest (alopecia X) in Pomeranian dogs

BACKGROUND

Hair cycle arrest (HCA) is a noninflammatory alopecic disease affecting various dog breeds, particularly Pomeranian dogs. This disease is probably a hereditary disorder considering the strong breed predisposition. Despite efforts to identify the pathogenesis of this disease, an underlying specific cause is unknown.

OBJECTIVE

To identify candidate gene mutations for HCA in Pomeranian dogs.

ANIMALS

Four Pomeranian dogs diagnosed with HCA and four unaffected Pomeranian dogs.

MATERIALS AND METHODS

Whole blood was used for DNA extraction. Whole-genome sequencing (WGS) was performed, and variants were analysed using a Genome Analysis Toolkit (GATK) and SnpEff. All reads were aligned to the reference genome, Dog10K_Boxer_Tasha. Sanger sequencing was performed to define the complex mutations.

RESULTS

A total of 113 variants of mitochondrial DNA were found to be effective gene mutations in the eight dogs. The affected dogs showed significantly increased effective mutations (average 57 variants) compared with unaffected dogs (average eight variants; p < 0.05). There was no significant difference in the number of chromosomal DNA mutations between the two groups.

CONCLUSION AND CLINICAL IMPORTANCE

We suggest that an increased number of mitochondrial gene mutations are features for HCA in Pomeranian dogs.

Screening and Carrier Rate of Neuronal Ceroid Lipofuscinosis in Chihuahua Dogs in Japan

Neuronal ceroid lipofuscinosis (NCL) is a group of rare lethal neurodegenerative lysosomal storage diseases that occur in a range of dog breeds, including Chihuahuas. Recently, a homozygous single base-pair deletion (c.846delT), which causes a frame shift generating a premature stop codon (p.Phe282Leufs13*) in the canine CLN7/MFSD8 gene, has been identified as a causative mutation for NCL in Chihuahuas. The objective of this study was to determine the frequency of the mutant allele and/or carrier rate of NCL in Chihuahuas in Japan using a newly designed real-time PCR assay. Samples of saliva were randomly collected from 1007 Chihuahua puppies during physical examinations prior to the transportation to pet shops. Screening results revealed a carrier rate of 1.29%, indicating a mutant allele frequency (0.00645) that is considered sufficiently high to warrant measures for the control and prevention of this lethal disease. The genotyping assay designed in this study could make a valuable contribution to the control and prevention of NCL.

Characterization of neurological disease progression in a canine model of CLN5 neuronal ceroid lipofuscinosis

Golden Retriever dogs with a frameshift variant in CLN5 (c.934_935delAG) suffer from a progressive neurodegenerative disorder analogous to the CLN5 form of neuronal ceroid lipofuscinosis (NCL). Five littermate puppies homozygous for the deletion allele were identified prior to the onset of disease signs. Studies were performed to characterize the onset and progression of the disease in these dogs. Neurological signs that included restlessness, unwillingness to cooperate with the handlers, and proprioceptive deficits first became apparent at approximately 12 months of age. The neurological signs progressed over time and by 21 to 23 months of age included general proprioceptive ataxia, menace response deficits, aggressive behaviors, cerebellar ataxia, intention tremors, decreased visual tracking, seizures, cognitive decline, and impaired prehension. Due to the severity of these signs, the dogs were euthanized between 21 and 23 months of age. Magnetic resonance imaging revealed pronounced progressive global brain atrophy with a more than sevenfold increase in the volume of the ventricular system between 9.5 and 22.5 months of age. Accompanying this atrophy were pronounced accumulations of autofluorescent inclusions throughout the brain and spinal cord. Ultrastructurally, the contents of these inclusions were found to consist primarily of membrane‐like aggregates. Inclusions with similar fluorescence properties were present in cardiac muscle. Similar to other forms of NCL, the affected dogs had low plasma carnitine concentrations, suggesting impaired carnitine biosynthesis. These data on disease progression will be useful in future studies using the canine model for therapeutic intervention studies.

Adult-Onset Neuronal Ceroid Lipofuscinosis in a Shikoku Inu

A two-year-and-eleven-month-old male Shikoku Inu was referred for evaluation of progressive gait abnormality that had begun three months prior. Neurological examination revealed ventral flexion of the neck, a wide-based stance in the hindlimb, wide excursions of the head from side to side, tremor in all four limbs, hypermetria in all four limbs, proprioceptive deficits in all four limbs, reduced patellar reflex in both hindlimbs, and postural vertical nystagmus. Later, behavioral and cognitive dysfunction, ataxia, and visual deficits slowly progressed. Magnetic resonance imaging revealed symmetrical progressive atrophy of the whole brain and cervical spinal cord. Bilateral retinal degeneration was observed, and both flush and flicker electroretinograms were bilaterally non-recordable at the age of five years and eight months, and the dog was euthanized. Histopathologically, faint-to-moderate deposition of light-brown pigments was frequently observed in the cytoplasm of neurons throughout the cerebrum, cerebellum, and nuclei of the brainstem. The pigments were positive for Luxol fast blue, periodic acid–Schiff, and Sudan black B, and exhibited autofluorescence. Electron microscopic examination revealed the accumulation of membranous material deposition in the neuronal cytoplasm. Small foci of pigment-containing macrophages were frequently observed around the capillary vessels. Based on these clinical and pathological findings, the animal was diagnosed with adult-onset neuronal ceroid lipofuscinosis.

Visual system pathology in a canine model of CLN5 neuronal ceroid lipofuscinosis

CLN5 neuronal ceroid lipofuscinosis is a hereditary neurodegenerative disease characterized by progressive neurological decline, vision loss and seizures. Visual impairment in children with CLN5 disease is attributed to a progressive decline in retinal function accompanied by retinal degeneration as well as impaired central nervous system function associated with global brain atrophy. We studied visual system pathology in five Golden Retriever littermates homozygous for the CLN5 disease allele previously identified in the breed. The dogs exhibited signs of pronounced visual impairment by 21-22 months of age. Electroretinogram recordings showed a progressive decline in retinal function primarily affecting cone neural pathways. Altered visual evoked potential recordings indicated that disease progression affected visual signal processing in the brain. Aside from several small retinal detachment lesions, no gross retinal abnormalities were observed with in vivo ocular imaging and histologically the retinas did not exhibit apparent abnormalities by 23 months of age. However, there was extensive accumulation of autofluorescent membrane-bound lysosomal storage bodies in almost all retinal layers, as well as in the occipital cortex, by 20 months of age. In the retina, storage was particularly pronounced in retinal ganglion cells, the retinal pigment epithelium and in photoreceptor cells just interior to the outer limiting membrane. The visual system pathology of CLN5-affected Golden Retrievers is similar to that seen early in the human disease. It was not possible to follow the dogs to an advanced stage of disease progression due to the severity of behavioral and motor disease signs by 23 months of age. The findings reported here indicate that canine CLN5 disease will be a useful model of visual system disease in CLN5 neuronal ceroid lipofuscinosis. The baseline data obtained in this investigation will be useful in future therapeutic intervention studies. The findings indicate that there is a fairly broad time frame after disease onset within which treatments could be effective in preserving vision.

A lysosomal enigma CLN5 and its significance in understanding neuronal ceroid lipofuscinosis

Neuronal Ceroid Lipofuscinosis (NCL), also known as Batten disease, is an incurable childhood brain disease. The thirteen forms of NCL are caused by mutations in thirteen CLN genes. Mutations in one CLN gene, CLN5, cause variant late-infantile NCL, with an age of onset between 4 and 7 years. The CLN5 protein is ubiquitously expressed in the majority of tissues studied and in the brain, CLN5 shows both neuronal and glial cell expression. Mutations in CLN5 are associated with the accumulation of autofluorescent storage material in lysosomes, the recycling units of the cell, in the brain and peripheral tissues. CLN5 resides in the lysosome and its function is still elusive. Initial studies suggested CLN5 was a transmembrane protein, which was later revealed to be processed into a soluble form. Multiple glycosylation sites have been reported, which may dictate its localisation and function. CLN5 interacts with several CLN proteins, and other lysosomal proteins, making it an important candidate to understand lysosomal biology. The existing knowledge on CLN5 biology stems from studies using several model organisms, including mice, sheep, cattle, dogs, social amoeba and cell cultures. Each model organism has its advantages and limitations, making it crucial to adopt a combinatorial approach, using both human cells and model organisms, to understand CLN5 pathologies and design drug therapies. In this comprehensive review, we have summarised and critiqued existing literature on CLN5 and have discussed the missing pieces of the puzzle that need to be addressed to develop an efficient therapy for CLN5 Batten disease.

International veterinary canine dyskinesia task force ECVN consensus statement: Terminology and classification

Movement disorders are a heterogeneous group of clinical syndromes in humans and animals characterized by involuntary movements without changes in consciousness. Canine movement disorders broadly include tremors, peripheral nerve hyperexcitability disorders, paroxysmal dyskinesia, and dystonia. Of these, canine paroxysmal dyskinesias remain one of the more difficult to identify and characterize in dogs. Canine paroxysmal dyskinesias include an array of movement disorders in which there is a recurrent episode of abnormal, involuntary, movement. In this consensus statement, we recommend standard terminology for describing the various movement disorders with an emphasis on paroxysmal dyskinesia, as well as a preliminary classification and clinical approach to reporting cases. In the clinical approach to movement disorders, we recommend categorizing movements into hyperkinetic vs hypokinetic, paroxysmal vs persistent, exercise‐induced vs not related to exercise, using a detailed description of movements using the recommended terminology presented here, differentiating movement disorders vs other differential diagnoses, and then finally, determining whether the paroxysmal dyskinesia is due to either inherited or acquired etiologies. This consensus statement represents a starting point for consistent reporting of clinical descriptions and terminology associated with canine movement disorders, with additional focus on paroxysmal dyskinesia. With consistent reporting and identification of additional genetic mutations responsible for these disorders, our understanding of the phenotype, genotype, and pathophysiology will continue to develop and inform further modification of these recommendations.

Evaluation of genetic diversity and management of disease in Border Collie dogs

Maintaining genetic diversity in dog breeds is an important consideration for the management of inherited diseases. We evaluated genetic diversity in Border Collies using molecular and genealogical methods, and examined changes to genetic diversity when carriers for Trapped Neutrophil Syndrome (TNS) and Neuronal Ceroid Lipofuscinosis (NCL) are removed from the genotyped population. Genotype data for 255 Border Collies and a pedigree database of 83,996 Border Collies were used for analysis. Molecular estimates revealed a mean multi-locus heterozygosity (MLH) of 0.311 (SD 0.027), 20.79% of the genome consisted of runs of homozygosity (ROH ) > 1 Mb, effective population size (N_e) was 84.7, and mean inbreeding (F) was 0.052 (SD 0.083). For 227 genotyped Border Collies that had available pedigree information (GenoPed), molecular and pedigree estimates of diversity were compared. A reference population (dogs born between 2005 and 2015, inclusive; N = 13,523; RefPop) and their ancestors (N = 12,478) were used to evaluate the diversity of the population that are contributing to the current generation. The reference population had a N_e of 123.5, a mean F of 0.095 (SD 0.082), 2276 founders (f), 205.5 effective founders (f_e), 28 effective ancestors (f_a) and 10.65 (SD 2.82) founder genomes (N_g). Removing TNS and NCL carriers from the genotyped population had a small impact on diversity measures (ROH > 1 Mb, MLH, heterozygosity), however, there was a loss of > 10% minor allele frequency for 89 SNPs around the TNS mutation (maximum loss of 12.7%), and a loss of > 5% for 5 SNPs around the NCL mutation (maximum 5.18%). A common ancestor was identified for 38 TNS-affected dogs and 64 TNS carriers, and a different common ancestor was identified for 33 NCL-affected dogs and 28 carriers, with some overlap of prominent individuals between both pedigrees. Overall, Border Collies have a high level of genetic diversity compared to other breeds.

Neuronal Ceroid Lipofuscinosis in a Domestic Cat Associated with a DNA Sequence Variant That Creates a Premature Stop Codon in CLN6

A neutered male domestic medium-haired cat presented at a veterinary neurology clinic at 20 months of age due to progressive neurological signs that included visual impairment, focal myoclonus, and frequent severe generalized seizures that were refractory to treatment with phenobarbital. Magnetic resonance imaging revealed diffuse global brain atrophy. Due to the severity and frequency of its seizures, the cat was euthanized at 22 months of age. Microscopic examination of the cerebellum, cerebral cortex and brainstem revealed pronounced intracellular accumulations of autofluorescent storage material and inflammation in all 3 brain regions. Ultrastructural examination of the storage material indicated that it consisted almost completely of tightly-packed membrane-like material. The clinical signs and neuropathology strongly suggested that the cat suffered from a form of neuronal ceroid lipofuscinosis (NCL). Whole exome sequence analysis was performed on genomic DNA from the affected cat. Comparison of the sequence data to whole exome sequence data from 39 unaffected cats and whole genome sequence data from an additional 195 unaffected cats revealed a homozygous variant in CLN6 that was unique to the affected cat. This variant was predicted to cause a stop gain in the transcript due to a guanine to adenine transition (ENSFCAT00000025909:c.668G > A; XM_003987007.5:c.668G > A) and was the sole loss of function variant detected. CLN6 variants in other species, including humans, dogs, and sheep, are associated with the CLN6 form of NCL. Based on the affected cat's clinical signs, neuropathology and molecular genetic analysis, we conclude that the cat's disorder resulted from the loss of function of CLN6. This study is only the second to identify the molecular genetic basis of a feline NCL. Other cats exhibiting similar signs can now be screened for the CLN6 variant. This could lead to establishment of a feline model of CLN6 disease that could be used in therapeutic intervention studies.

Experimental gene therapies for the NCLs

The neuronal ceroid lipofuscinoses (NCLs), also known as Batten disease, are a group of rare monogenic neurodegenerative diseases predominantly affecting children. All NCLs are lethal and incurable and only one has an approved treatment available. To date, 13 NCL subtypes (CLN1-8, CLN10-14) have been identified, based on the particular disease-causing defective gene. The exact functions of NCL proteins and the pathological mechanisms underlying the diseases are still unclear. However, gene therapy has emerged as an attractive therapeutic strategy for this group of conditions. Here we provide a short review discussing updates on the current gene therapy studies for the NCLs.

Cognitive Abilities of Dogs with Mucopolysaccharidosis I: Learning and Memory

Mucopolysaccharidosis I (MPS I) results from a deficiency of a lysosomal enzyme, alpha-L-iduronidase (IDUA). IDUA deficiency leads to glycosaminoglycan (GAG) accumulation resulting in cellular degeneration and multi-organ dysfunction. The primary aims of this pilot study were to determine the feasibility of cognitive testing MPS I affected dogs and to determine their non-social cognitive abilities with and without gene therapy. Fourteen dogs were tested: 5 MPS I untreated, 5 MPS I treated, and 4 clinically normal. The treated group received intrathecal gene therapy as neonates to replace the IDUA gene. Cognitive tests included delayed non-match to position (DNMP), two-object visual discrimination (VD), reversal learning (RL), attention oddity (AO), and two-scent discrimination (SD). Responses were recorded as correct, incorrect, or no response, and analyzed using mixed effect logistic regression analysis. Significant differences were not observed among the three groups for DNMP, VD, RL, or AO. The MPS I untreated dogs were excluded from AO testing due to failing to pass acquisition of the task, potentially representing a learning or executive function deficit. The MPS I affected group (treated and untreated) was significantly more likely to discriminate between scents than the normal group, which may be due to an age effect. The normal group was comprised of the oldest dogs, and a mixed effect logistic model indicated that older dogs were more likely to respond incorrectly on scent discrimination. Overall, this study found that cognition testing of MPS I affected dogs to be feasible. This work provides a framework to refine future cognition studies of dogs affected with diseases, including MPS I, in order to assess therapies in a more comprehensive manner.

The contribution of multicellular model organisms to neuronal ceroid lipofuscinosis research

The NCLs (neuronal ceroid lipofuscinosis) are forms of neurodegenerative disease that affect people of all ages and ethnicities but are most prevalent in children. Commonly known as Batten disease, this debilitating neurological disorder is comprised of 13 different subtypes that are categorized based on the particular gene that is mutated (CLN1-8, CLN10-14). The pathological mechanisms underlying the NCLs are not well understood due to our poor understanding of the functions of NCL proteins. Only one specific treatment (enzyme replacement therapy) is approved, which is for the treating the brain in CLN2 disease. Hence there remains a desperate need for further research into disease-modifying treatments. In this review, we present and evaluate the genes, proteins and studies performed in the social amoeba, nematode, fruit fly, zebrafish, mouse and large animals pertinent to NCL. In particular, we highlight the use of multicellular model organisms to study NCL protein function, pathology and pathomechanisms. Their use in testing novel therapeutic approaches is also presented. With this information, we highlight how future research in these systems may be able to provide new insight into NCL protein functions in human cells and aid in the development of new therapies.

Neuronal ceroid lipofuscinosis in a German Shorthaired Pointer associated with a previously reported CLN8 nonsense variant

Two littermate German Shorthaired Pointers, a male and a female, were adopted as puppies from an animal shelter. Both puppies developed normally until approximately 11 months of age when the male began to exhibit neurological signs including ataxia, vision loss, and behavioral changes indicative of cognitive decline. These signs increased in severity over time. The female remained neurologically normal and healthy. The affected dog was euthanized at approximately 21 months of age. Autofluorescent cytoplasmic storage bodies were detected in neurons in unstained tissue sections from the cerebellum, the cerebrum, and the retina. Electron micrographs of these storage bodies showed that they were membrane bound and that most contained tightly packed aggregates of membranous whorls along with a variety of other ultrastructural features. This ultrastructure, along with the autofluorescence and the clinical signs supported a diagnosis of neuronal ceroid lipofuscinosis (NCL). Unlike earlier investigated forms of canine NCL with causal alleles in ATP13A2, TPP1, MFSD8 and CLN5 that had autofluorescent cytoplasmic storage bodies in cardiac muscle, no autofluorescence was detected in cardiac muscle from the affected German Shorthaired Pointer. A 39-fold average coverage whole genome sequence indicated that the affected German Shorthaired Pointer was homozygous for the A allele of a G > A transversion at position 30,895,648 chromosome 37. This 37:30895648G > A mutation created a CLN8 termination codon that had been previously reported to cause NCL in a mixed breed dog with Australian Shepherd and Australian Cattle Dog ancestry. This nonsense allele was heterozygous in the clinically normal female sibling, while archived DNA samples from 512 other German Shorthaired Pointers were all homozygous for the reference allele. The affected German Shorthaired Pointer and the previously diagnosed mixed breed dog with the same nonsense mutation shaired an identical homozygous haplotype that extended for 4.41 Mb at the telomeric end of chromosome 37, indicating the both dogs inherited the nonsense mutation from a common ancestor.

ATP13A2 missense variant in Australian Cattle Dogs with late onset neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage disorders characterized by progressive neurodegeneration and declines in neurological functions. Pathogenic sequence variants in at least 13 genes underlie different forms of NCL, almost all of which are recessively inherited. To date 13 sequence variants in 8 canine orthologs of human NCL genes have been found to occur in 11 dog breeds in which they result in progressive neurological disorders similar to human NCLs. Canine NCLs can serve as models for preclinical evaluation of therapeutic interventions for these disorders. In most NCLs, the onset of neurological signs occurs in childhood, but some forms have adult onsets. Among these is CLN12 disease, also known as Kufor-Rakeb syndrome, PARK9, and spastic paraplegia78. These disorders result from variants in ATP13A2 which encodes a putative transmembrane ion transporter important for lysosomal function. Three Australian Cattle Dogs (a female and two of her offspring) were identified with a progressive neurological disorder with an onset of clinical signs at approximately 6 years of age. The affected dogs exhibited clinical courses and histopathology characteristic of the NCLs. Whole genome sequence analysis of one of these dogs revealed a homozygous c.1118C > T variant in ATP13A2 that predicts a nonconservative p.(Thr373Ile) amino acid substitution. All 3 affected dogs were homozygous for this variant, which was heterozygous in 42 of 394 unaffected Australian Cattle Dogs, the remainder of which were homozygous for the c.1118C allele. The high frequency of the mutant allele in this breed suggests that further screening for this variant should identify additional homozygous dogs and indicates that it would be advisable to perform such screening prior to breeding Australian Cattle Dogs.

A mixed breed dog with neuronal ceroid lipofuscinosis is homozygous for a CLN5 nonsense mutation previously identified in Border Collies and Australian Cattle Dogs

The neuronal ceroid lipofuscinoses (NCLs) are a group of inherited neurodegenerative disorders characterized by progressive declines in neurological functions following normal development. The NCLs are distinguished from similar disorders by the accumulation of autofluorescent lysosomal storage bodies in neurons and many other cell types, and are classified as lysosomal storage diseases. At least 13 genes contain pathogenic sequence variants that underlie different forms of NCL. Naturally occurring canine NCLs can serve as models to develop better understanding of the disease pathologies and for preclinical evaluation of therapeutic interventions for these disorders. To date 14 sequence variants in 8 canine orthologs of human NCL genes have been found to cause progressive neurological disorders similar to human NCLs in 12 different dog breeds. A mixed breed dog with parents of uncertain breed background developed progressive neurological signs consistent with NCL starting at approximately 11 to 12 months of age, and when evaluated with magnetic resonance imaging at 21 months of age exhibited diffuse brain atrophy. Due to the severity of neurological decline the dog was euthanized at 23 months of age. Cerebellar and cerebral cortical neurons contained massive accumulations of autofluorescent storage bodies the contents of which had the appearance of tightly packed membranes. A whole genome sequence, generated with DNA from the affected dog contained a homozygous C-to-T transition at position 30,574,637 on chromosome 22 which is reflected in the mature CLN5 transcript (CLN5: c.619C > T) and converts a glutamine codon to a termination codon (p.Gln207Ter). The identical nonsense mutation has been previously associated with NCL in Border Collies, Australian Cattle Dogs, and a German Shepherd-Australian Cattle Dog mix. The current whole genome sequence and a previously generated whole genome sequence for an Australian Cattle Dog with NCL share a rare homozygous haplotype that extends for 87 kb surrounding 22: 30, 574, 637 and includes 21 polymorphic sites. When genotyped at 7 of these polymorphic sites, DNA samples from the German Shepherd-Australian Cattle Dog mix and from 5 Border Collies with NCL that were homozygous for the CLN5: c.619 T allele also shared this homozygous haplotype, suggesting that the NCL in all of these dogs stems from the same founding mutation event that may have predated the establishment of the modern dog breeds. If so, the CLN5 nonsence allele is probably segregating in other, as yet unidentified, breeds. Thus, dogs exhibiting similar NCL-like signs should be screened for this CLN5 nonsense allele regardless of breed.

Novel Mutations in CLN5 of Chinese Patients With Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinosis is a hereditary disease, and ceroid-lipofuscinosis neuronal protein 5 (CLN5) has been proved to be associated with neuronal ceroid lipofuscinosis. Here we report 3 patients from 2 families diagnosed with CLN5 neuronal ceroid lipofuscinosis. Whole genome sequencing of DNAs from 3 patients and their families revealed 3 novel homozygous mutations, including 1 deletion CLN5.c718 719delAT and 2 missense mutations c.1082T>C and c.623G>A. We reviewed 278 papers about neuronal ceroid lipofuscinosis resulting from CLN5 mutations and compared Chinese cases with 27 European and American cases. The overall age of onset of European and American patients occur mainly at 3 to 6 years (66%, 18/27), 100% (27/27) of patients had psychomotor regression, 99% (26/27) patients presented vision decline, and 70% (19/27) of patients suffered seizures. In China, the age of onset in 3 patients was 5 years, but for 1 patient it was at 17 months. Four Chinese patients presented psychomotor deterioration and seizures; only 1 had visual problems.

Two mixed breed dogs with sensory neuropathy are homozygous for an inversion disrupting FAM134B previously identified in Border Collies

Two unrelated 8‐month‐old male mixed breed dogs were presented for evaluation of progressive ataxia, knuckling, and lack of pain perception in the distal limbs. Because of the similarity in age of onset, progression, and clinical findings with previously described sensory neuropathy in Border Collies, the affected dogs were screened for an FAM134B mutation and were determined to be homozygous for the mutation. Despite few phenotypic similarities with other breeds, genetic testing for specific diseases should be considered in mixed breed dogs with compatible clinical signs, especially if ancestry is unknown.

Canine neuronal ceroid lipofuscinoses: Promising models for preclinical testing of therapeutic interventions

The neuronal ceroid lipofuscinoses (NCLs) are devastating inherited progressive neurodegenerative diseases, with most forms having a childhood onset of clinical signs. The NCLs are characterized by progressive cognitive and motor decline, vision loss, seizures, respiratory and swallowing impairment, and ultimately premature death. Different forms of NCL result from mutations in at least 13 genes. The clinical signs of some forms overlap significantly, so genetic testing is the only way to definitively determine which form an individual patient suffers from. At present, an effective treatment is available for only one form of NCL. Evidence of NCL has been documented in over 20 canine breeds and in mixed-breed dogs. To date, 12 mutations in 8 different genes orthologous to the human NCL genes have been found to underlie NCL in a variety of dog breeds. A Dachshund model with a null mutation in one of these genes is being utilized to investigate potential therapeutic interventions, including enzyme replacement and gene therapies. Demonstration of the efficacy of enzyme replacement therapy in this model led to successful completion of human clinical trials of this treatment. Further research into the other canine NCLs, with in-depth characterization and understanding of the disease processes, will likely lead to the development of successful therapeutic interventions for additional forms of NCL, for both human patients and animals with these disorders.

GM2 Gangliosidosis in Shiba Inu Dogs with an In-Frame Deletion in HEXB

Consistent with a tentative diagnosis of neuronal ceroid lipofuscinosis (NCL), autofluorescent cytoplasmic storage bodies were found in neurons from the brains of 2 related Shiba Inu dogs with a young‐adult onset, progressive neurodegenerative disease. Unexpectedly, no potentially causal NCL‐related variants were identified in a whole‐genome sequence generated with DNA from 1 of the affected dogs. Instead, the whole‐genome sequence contained a homozygous 3 base pair (bp) deletion in a coding region of HEXB. The other affected dog also was homozygous for this 3‐bp deletion. Mutations in the human HEXB ortholog cause Sandhoff disease, a type of GM2 gangliosidosis. Thin‐layer chromatography confirmed that GM2 ganglioside had accumulated in an affected Shiba Inu brain. Enzymatic analysis confirmed that the GM2 gangliosidosis resulted from a deficiency in the HEXB encoded protein and not from a deficiency in products from HEXA or GM2A, which are known alternative causes of GM2 gangliosidosis. We conclude that the homozygous 3‐bp deletion in HEXB is the likely cause of the Shiba Inu neurodegenerative disease and that whole‐genome sequencing can lead to the early identification of potentially disease‐causing DNA variants thereby refocusing subsequent diagnostic analyses toward confirming or refuting candidate variant causality.

Classification of Involuntary Movements in Dogs: Myoclonus and Myotonia

Myoclonus is a sudden brief, involuntary muscle jerk. Of all the movement disorders, myoclonus is the most difficult to encapsulate into any simple framework. On the one hand, a classification system is required that is clinically useful to aid in guiding diagnosis and treatment. On the other hand, there is need for a system that organizes current knowledge regarding biological mechanisms to guide scientific research. These 2 needs are distinct, making it challenging to develop a robust classification system suitable for all purposes. We attempt to classify myoclonus as “epileptic” and “nonepileptic” based on its association with epileptic seizures. Myotonia in people may be divided into 2 clinically and molecularly defined forms: (1) nondystrophic myotonias and (2) myotonic dystrophies. The former are a group of skeletal muscle channelopathies characterized by delayed skeletal muscle relaxation. Many distinct clinical phenotypes are recognized in people, the majority relating to mutations in skeletal muscle voltage‐gated chloride (CLCN1) and sodium channel (SCN4A) genes. In dogs, myotonia is associated with mutations in CLCN1. The myotonic dystrophies are considered a multisystem clinical syndrome in people encompassing 2 clinically and molecularly defined forms designated myotonic dystrophy types 1 and 2. No mutation has been linked to veterinary muscular dystrophies. We detail veterinary examples of myotonia and attempt classification according to guidelines used in humans. This more precise categorization of myoclonus and myotonia aims to promote the search for molecular markers contributing to the phenotypic spectrum of disease. Our work aimed to assist recognition for these 2 enigmatic conditions.

Neuronal ceroid lipofuscinosis (NCL) is caused by the entire deletion of CLN8 in the Alpenländische Dachsbracke dog

Neuronal ceroid lipofuscinoses (NCLs) are inherited lysosomal storage diseases that have been described in a variety of dog breeds, where they are caused by different mutations in different genes. However, the causative gene defect in the breed Alpenländische Dachsbracke remained unknown so far. Here we present two confirmed cases of NCL in Alpenländische Dachsbracke dogs from different litters of the same sire with a different dam harboring the same underlying novel mutation in the CLN8 gene. Case 1, a 2-year-old male Alpenländische Dachsbracke was presented with neurological signs including disorientation, character changes including anxiety states and aggressiveness, sudden blindness and reduction of food intake. Magnetic resonance imaging (MRI) scans showed cerebral atrophy with dilation of all cerebral ventricles, thinning of the intermediate mass of the thalamus and widening of the cerebral sulci. Postmortem examination of the central nervous system (CNS) showed neuronal loss in the cerebral cortex, cerebellum and spinal cord with massive intracellular deposits of ceroid pigment. Additional ceroid-lipofuscin deposits were observed in the enteric nervous system and in macrophages within spleen, lymph nodes and lung. Ultrastructural analyses confirmed NCL with the presence of osmiophilic membrane bounded lamellar-like structures. Case 2, a 1,5-year old female Alpenländische Dachsbracke was presented with progressive generalized forebrain disease including mental changes such as fearful reactions to various kinds of external stimuli and disorientation. The dog also displayed seizures, absence of menace reactions and negative cotton-ball test with normal pupillary light reactions. The clinical and post mortem examination yielded similar results in the brain as in Case 1. Whole genome sequencing of Case 1 and PCR results of both cases revealed a homozygous deletion encompassing the entire CLN8 gene as the most likely causative mutation for the NCL form observed in both cases. The deletion follows recessive inheritance since the dam and a healthy male littermate of Case 1 were tested as heterozygous carriers. This is the first detailed description of CLN8 gene associated NCL in Alpenländische Dachsbracke dogs and thus provides a novel canine CLN8 model for this lysosomal storage disease. The presence of ceroid lipofuscin in extracerebral tissues may help to confirm the diagnosis of NCL in vivo, especially in new dog breeds where the underlying mutation is not known.

Extraneuronal pathology in a canine model of CLN2 neuronal ceroid lipofuscinosis after intracerebroventricular gene therapy that delays neurological disease progression

CLN2 neuronal ceroid lipofuscinosis is a hereditary lysosomal storage disease with primarily neurological signs that results from mutations in TPP1, which encodes the lysosomal enzyme tripeptidyl peptidase-1 (TPP1). Studies using a canine model for this disorder demonstrated that delivery of TPP1 enzyme to the cerebrospinal fluid (CSF) by intracerebroventricular administration of an AAV-TPP1 vector resulted in substantial delays in the onset and progression of neurological signs and prolongation of life span. We hypothesized that the treatment may not deliver therapeutic levels of this protein to tissues outside the central nervous system that also require TPP1 for normal lysosomal function. To test this hypothesis, dogs treated with CSF administration of AAV-TPP1 were evaluated for the development of non-neuronal pathology. Affected treated dogs exhibited progressive cardiac pathology reflected by elevated plasma cardiac troponin-1, impaired cardiac function and development of histopathological myocardial lesions. Progressive increases in the plasma activity levels of alanine aminotransferase and creatine kinase indicated development of pathology in the liver and muscles. The treatment also did not prevent disease-related accumulation of lysosomal storage bodies in the heart or liver. These studies indicate that optimal treatment outcomes for CLN2 disease may require delivery of TPP1 systemically as well as directly to the central nervous system.

Homozygous PPT1 Splice Donor Mutation in a Cane Corso Dog With Neuronal Ceroid Lipofuscinosis

A 10‐month‐old spayed female Cane Corso dog was evaluated after a 2‐month history of progressive blindness, ataxia, and lethargy. Neurologic examination abnormalities indicated a multifocal lesion with primarily cerebral and cerebellar signs. Clinical worsening resulted in humane euthanasia. On necropsy, there was marked astrogliosis throughout white matter tracts of the cerebrum, most prominently in the corpus callosum. In the cerebral cortex and midbrain, most neurons contained large amounts of autofluorescent storage material in the perinuclear area of the cells. Cerebellar storage material was present in the Purkinje cells, granular cell layer, and perinuclear regions of neurons in the deep nuclei. Neuronal ceroid lipofuscinosis (NCL) was diagnosed. Whole genome sequencing identified a PPT1c.124 + 1G>A splice donor mutation. This nonreference assembly allele was homozygous in the affected dog, has not previously been reported in dbSNP, and was absent from the whole genome sequences of 45 control dogs and 31 unaffected Cane Corsos. Our findings indicate a novel mutation causing the CLN1 form of NCL in a previously unreported dog breed. A canine model for CLN1 disease could provide an opportunity for therapeutic advancement, benefiting both humans and dogs with this disorder.

Neuronal ceroid lipofuscinosis associated with an MFSD8 mutation in Chihuahuas

The neuronal ceroid lipofuscinoses (NCLs) are hereditary neurodegenerative disorders characterized by progressive declines in neurological functions, seizures, and premature death. NCLs result from mutations in at least 13 different genes. Canine versions of the NCLs can serve as important models in developing effective therapeutic interventions for these diseases. NCLs have been described in a number of dog breeds, including Chihuahuas. Studies were undertaken to further characterize the pathology of Chihuahua NCL and to verify its molecular genetic basis. Four unrelated client owned Chihuahuas from Japan, Italy and England that exhibited progressive neurological signs consistent with a diagnosis of NCL underwent neurological examinations. Brain and in some cases also retinal and heart tissues were examined postmortem for the presence of lysosomal storage bodies characteristic of NCL. The affected dogs exhibited massive accumulation of autofluorescent lysosomal storage bodies in the brain, retina and heart accompanied by brain atrophy and retinal degeneration. The dogs were screened for known canine NCL mutations previously reported in a variety of dog breeds. All 4 dogs were homozygous for the MFSD8 single base pair deletion (MFSD8:c.843delT) previously associated with NCL in a Chinese Crested dog and in 2 affected littermate Chihuahuas from Scotland. The dogs were all homozygous for the normal alleles at the other genetic loci known to cause different forms of canine NCL. The MFSD8:c.843delT mutation was not present in 57 Chihuahuas that were either clinically normal or suffered from unrelated diseases or in 1761 unaffected dogs representing 186 other breeds. Based on these data it is almost certain that the MFSD8:c.843delT mutation is the cause of NCL in Chihuahuas. Because the disorder occurred in widely separated geographic locations or in unrelated dogs from the same country, it is likely that the mutant allele is widespread among Chihuahuas. Genetic testing for this mutation in other Chihuahuas is therefore likely to identify intact dogs with the mutant allele that could be used to establish a research colony that could be used to test potential therapeutic interventions for the corresponding human disease.