GM2 gangliosidosis variant 0 (Sandhoff-like disease) in a family of toy poodles

Positioning Head Tilt in Canine Lysosomal Storage Disease: A Retrospective Observational Descriptive Study

Positioning head tilt is a neurological sign that has recently been described in dogs with congenital cerebellar malformations. This head tilt is triggered in response to head movement and is believed to be caused by a lack of inhibition of the vestibular nuclei by the cerebellar nodulus and ventral uvula (NU), as originally reported cases were dogs with NU hypoplasia. We hypothesized that other diseases, such as lysosomal storage diseases that cause degeneration in the whole brain, including NU, may cause NU dysfunction and positioning head tilt. Videos of the clinical signs of canine lysosomal storage disease were retrospectively evaluated. In addition, post-mortem NU specimens from each dog were histopathologically evaluated. Nine dogs were included, five with lysosomal storage disease, two Chihuahuas with neuronal ceroid lipofuscinosis (NCL), two Border Collies with NCL, one Shikoku Inu with NCL, two Toy Poodles with GM2 gangliosidosis, and two Shiba Inus with GM1 gangliosidosis. Twenty-eight videos recorded the clinical signs of the dogs. In these videos, positioning head tilt was observed in seven of nine dogs, two Chihuahuas with NCL, one Border Collie with NCL, one Shikoku Inu with NCL, one Toy Poodle with GM2 gangliosidosis, and two Shiba Inus with GM1 gangliosidosis. Neuronal degeneration and loss of NU were histopathologically confirmed in all diseases. As positioning head tilt had not been described until 2016, it may have been overlooked and may be a common clinical sign and pathophysiology in dogs with NU dysfunction.

THE LYSOSOMAL STORAGE DISEASE GM2 GANGLIOSIDOSIS IN CAPTIVE BANDED MONGOOSE SIBLINGS ( MUNGOS MUNGO)

  This study reports the occurrence of the lysosomal storage disease GM2 gangliosidosis (Sandhoff disease) in two 11-mo-old captive-bred, male and female mongoose siblings ( Mungos mungo). The clinical signs and the pathological findings reported here were similar to those reported in other mammalian species. Light microscopy revealed an accumulation of stored material in neurons and macrophages accompanied by a significant neuronal degeneration (swelling of neuronal soma, loss of Nissl substance, and neuronal loss) and gliosis. Electron microscopy of brain tissue identified the stored material as membrane-bound multilamellar bodies. An almost complete lack of total hexosaminidase activity in serum suggested a defect in the HEXB gene (Sandhoff disease in humans). High-performance thin-layer chromatography and mass spectrometry confirmed the accumulation of GM2 ganglioside in brain and kidney tissue, and the lectin staining pattern of the brain tissue further corroborated the diagnosis of a Sandhoff-type lysosomal storage disease.

Two-Year Follow-Up Magnetic Resonance Imaging and Spectroscopy Findings and Cerebrospinal Fluid Analysis of a Dog with Sandhoff's Disease

A 13‐month‐old female Toy Poodle was presented for progressive ataxia and intention tremors of head movement. The diagnosis of Sandhoff's disease (GM2 gangliosidosis) was confirmed by deficient β‐N‐acetylhexosaminidase A and B activity in circulating leukocytes and identification of the homozygous mutation (HEXB: c.283delG). White matter in the cerebrum and cerebellum was hyperintense on T2‐weighted and fluid‐attenuated inversion recovery magnetic resonance images. Over the next 2 years, the white matter lesions expanded, and bilateral lesions appeared in the cerebellum and thalamus, associated with clinical deterioration. Magnetic resonance spectroscopy showed progressive decrease in brain N‐acetylaspartate, and glycine‐myo‐inositol and lactate‐alanine were increased in the terminal clinical stage. The concentrations of myelin basic protein and neuron specific enolase in cerebrospinal fluid were persistently increased. Imaging and spectroscopic appearance correlated with histopathological findings of severe myelin loss in cerebral and cerebellar white matter and destruction of the majority of cerebral and cerebellar neurons.

Canine GM2-Gangliosidosis Sandhoff Disease Associated with a 3-Base Pair Deletion in the HEXB Gene

BACKGROUND

GM2-gangliosidosis is a fatal neurodegenerative lysosomal storage disease (LSD) caused by deficiency of either β-hexosaminidase A (Hex-A) and β-hexosaminidase B (Hex-B) together, or the GM2 activator protein. Clinical signs can be variable and are not pathognomonic for the specific, causal deficiency.

OBJECTIVES

To characterize the phenotype and genotype of GM2-gangliosidosis disease in an affected dog.

ANIMALS

One affected Shiba Inu and a clinically healthy dog.

METHODS

Clinical and neurologic evaluation, brain magnetic resonance imaging (MRI), assays of lysosomal enzyme activities, and sequencing of all coding regions of HEXA, HEXB, and GM2A genes.

RESULTS

A 14-month-old, female Shiba Inu presented with clinical signs resembling GM2-gangliosidosis in humans and GM1-gangliosidosis in the Shiba Inu. Magnetic resonance imaging (MRI) of the dog's brain indicated neurodegenerative disease, and evaluation of cerebrospinal fluid (CSF) identified storage granules in leukocytes. Lysosomal enzyme assays of plasma and leukocytes showed deficiencies of Hex-A and Hex-B activities in both tissues. Genetic analysis identified a homozygous, 3-base pair deletion in the HEXB gene (c.618-620delCCT).

CONCLUSIONS AND CLINICAL IMPORTANCE

Clinical, biochemical, and molecular features are characterized in a Shiba Inu with GM2-gangliosidosis. The deletion of 3 adjacent base pairs in HEXB predicts the loss of a leucine residue at amino acid position 207 (p.Leu207del) supporting the hypothesis that GM2-gangliosidosis seen in this dog is the Sandhoff type. Because GM1-gangliosidosis also exists in this breed with almost identical clinical signs, genetic testing for both GM1- and GM2-gangliosidosis should be considered to make a definitive diagnosis.

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.

GM2 Gangliosidosis Variant 0 (Sandhoff Disease) in a Mixed-Breed Dog

GM2 gangliosidosis variant 0 (Sandhoff disease, SD) is a fatal, progressive, neurodegenerative lysosomal storage disease caused by simultaneous deficiencies of acid β-hexosaminidases A and B. Canine SD has so far been identified only in two purebreeds. In this article, we present the case of a 10 mo old, male dog of mixed breed that developed progressive neurological signs including ataxia, postural deficit, and visual deficits and finally died at the age of 21 mo. The dog was diagnosed with SD on the basis of the results of biochemical and histopathological analyses. This is the third report of canine SD and the first time it has been identified in a mixed breed.

Animal models of GM2 gangliosidosis: utility and limitations

GM2 gangliosidosis, a subset of lysosomal storage disorders, is caused by a deficiency of the glycohydrolase, β-N-acetylhexosaminidase, and includes the closely related Tay–Sachs and Sandhoff diseases. The enzyme deficiency prevents the normal, stepwise degradation of ganglioside, which accumulates unchecked within the cellular lysosome, particularly in neurons. As a result, individuals with GM2 gangliosidosis experience progressive neurological diseases including motor deficits, progressive weakness and hypotonia, decreased responsiveness, vision deterioration, and seizures. Mice and cats are well-established animal models for Sandhoff disease, whereas Jacob sheep are the only known laboratory animal model of Tay–Sachs disease to exhibit clinical symptoms. Since the human diseases are relatively rare, animal models are indispensable tools for further study of pathogenesis and for development of potential treatments. Though no effective treatments for gangliosidoses currently exist, animal models have been used to test promising experimental therapies. Herein, the utility and limitations of gangliosidosis animal models and how they have contributed to the development of potential new treatments are described.

In situ detection of GM1 and GM2 gangliosides using immunohistochemical and immunofluorescent techniques for auxiliary diagnosis of canine and feline gangliosidoses

Background

GM1 and GM2 gangliosidoses are progressive neurodegenerative lysosomal storage diseases resulting from the excessive accumulation of GM1 and GM2 gangliosides in the lysosomes, respectively. The diagnosis of gangliosidosis is carried out based on comprehensive findings using various types of specimens for histological, ultrastructural, biochemical and genetic analyses. Therefore, the partial absence or lack of specimens might have resulted in many undiagnosed cases. The aim of the present study was to establish immunohistochemical and immunofluorescent techniques for the auxiliary diagnosis of canine and feline gangliosidoses, using paraffin-embedded brain specimens stored for a long period.

Results

Using hematoxylin and eosin staining, cytoplasmic accumulation of pale to eosinophilic granular materials in swollen neurons was observed in animals previously diagnosed with GM1 or GM2 gangliosidosis. The immunohistochemical and immunofluorescent techniques developed in this study clearly demonstrated the accumulated material to be either GM1 or GM2 ganglioside.

Conclusions

Immunohistochemical and immunofluorescent techniques using stored paraffin-embedded brain specimens are useful for the retrospective diagnosis of GM1 and GM2 gangliosidoses in dogs and cats.

GM1 gangliosidosis in a Japanese domestic cat: a new variant identified in Hokkaido, Japan

A male Japanese domestic cat with retarded growth in Hokkaido, Japan, showed progressive motor dysfunction, such as ataxia starting at 3 months of age and tremors, visual disorder and seizure after 4 months of age. Finally, the cat died of neurological deterioration at 9 months of age. Approximately half of the peripheral blood lymphocytes had multiple abnormal vacuoles. Magnetic resonance imaging showed bisymmetrical hyperintensity in the white matter of the parietal and occipital lobes in the forebrain on T2-weighted and fluid-attenuated inversion recovery images, and mild encephalatrophy of the olfactory bulbs and temporal lobes. The activity of lysosomal acid β-galactosidase in leukocytes was negligible, resulting in the biochemical diagnosis of GM1 gangliosidosis. Histologically, swollen neurons characterized by accumulation of pale, slightly granular cytoplasmic materials were observed throughout the central nervous system. Dysmyelination or demyelination and gemistocytic astrocytosis were observed in the white matter. Ultrastructually, membranous cytoplasmic bodies were detected in the lysosomes of neurons. However, genetic analysis did not identify the c.1448G>C mutation, which is the single known mutation of feline GM1 gangliosidosis, suggesting that the cat was affected with a new variant of the feline disease.

Magnetic resonance findings of the corpus callosum in canine and feline lysosomal storage diseases

Several reports have described magnetic resonance (MR) findings in canine and feline lysosomal storage diseases such as gangliosidoses and neuronal ceroid lipofuscinosis. Although most of those studies described the signal intensities of white matter in the cerebrum, findings of the corpus callosum were not described in detail. A retrospective study was conducted on MR findings of the corpus callosum as well as the rostral commissure and the fornix in 18 cases of canine and feline lysosomal storage diseases. This included 6 Shiba Inu dogs and 2 domestic shorthair cats with GM1 gangliosidosis; 2 domestic shorthair cats, 2 familial toy poodles, and a golden retriever with GM2 gangliosidosis; and 2 border collies and 3 chihuahuas with neuronal ceroid lipofuscinoses, to determine whether changes of the corpus callosum is an imaging indicator of those diseases. The corpus callosum and the rostral commissure were difficult to recognize in all cases of juvenile-onset gangliosidoses (GM1 gangliosidosis in Shiba Inu dogs and domestic shorthair cats and GM2 gangliosidosis in domestic shorthair cats) and GM2 gangliosidosis in toy poodles with late juvenile-onset. In contrast, the corpus callosum and the rostral commissure were confirmed in cases of GM2 gangliosidosis in a golden retriever and canine neuronal ceroid lipofuscinoses with late juvenile- to early adult-onset, but were extremely thin. Abnormal findings of the corpus callosum on midline sagittal images may be a useful imaging indicator for suspecting lysosomal storage diseases, especially hypoplasia (underdevelopment) of the corpus callosum in juvenile-onset gangliosidoses.

Real-time PCR genotyping assay for GM2 gangliosidosis variant 0 in toy poodles and the mutant allele frequency in Japan

GM2 gangliosidosis variant 0 (Sandhoff disease, SD) is a fatal, progressive neurodegenerative lysosomal storage disease caused by mutations of the HEXB gene. In canine SD, a pathogenic mutation (c.283delG) of the canine HEXB gene has been identified in toy poodles. In the present study, a TaqMan probe-based real-time PCR genotyping assay was developed and evaluated for rapid and large-scale genotyping and screening for this mutation. Furthermore, a genotyping survey was carried out in a population of toy poodles in Japan to determine the current mutant allele frequency. The real-time PCR assay clearly showed all genotypes of canine SD. The assay was suitable for large-scale survey as well as diagnosis, because of its high throughput and rapidity. The genotyping survey demonstrated a carrier frequency of 0.2%, suggesting that the current mutant allele frequency is low in Japan. However, there may be population stratification in different places, because of the founder effect by some carriers. Therefore, this new assay will be useful for the prevention and control of SD in toy poodles.

Anti-GM2 ganglioside antibodies are a biomarker for acute canine polyradiculoneuritis

Acute canine polyradiculoneuritis (ACP) is considered to be the canine equivalent of the human peripheral nerve disorder Guillain-Barré syndrome (GBS); an aetiological relationship, however, remains to be demonstrated. In GBS, anti-glycolipid antibodies (Abs) are considered as important disease mediators. To address the possibility of common Ab biomarkers, the sera of 25 ACP dogs, 19 non-neurological, and 15 epileptic control dogs were screened for IgG Abs to 10 glycolipids and their 1 : 1 heteromeric complexes using combinatorial glycoarrays. Anti-GM2 ganglioside Abs were detected in 14/25 ACP dogs, and anti-GA1 Abs in one further dog. All controls except for one were negative for anti-glycolipid Abs. In this cohort of cases and controls, the glycoarray screen reached a diagnostic sensitivity of 60% and a specificity of 97%; a lower sensitivity (32%) was reported using a conventional glycolipid ELISA. To address the possible pathogenic role for anti-GM2 Abs in ACP, we identified GM2 in canine sciatic nerve by both mass spectrometry and thin layer chromatography overlay. In immunohistological studies, GM2 was localized predominantly to the abaxonal Schwann cell membrane. The presence of anti-GM2 Abs in ACP suggests that it may share a similar pathophysiology with GBS, for which it could thus be considered a naturally occurring animal model.

Magnetic resonance imaging and genetic investigation of a case of Rottweiler leukoencephalomyelopathy

Background

Leukoencephalomyelopathy is an inherited neurodegenerative disorder that affects the white matter of the spinal cord and brain and is known to occur in the Rottweiler breed. Due to the lack of a genetic test for this disorder, post mortem neuropathological examinations are required to confirm the diagnosis. Leukoencephalopathy with brain stem and spinal cord involvement and elevated lactate levels is a rare, autosomal recessive disorder in humans that was recently described to have clinical features and magnetic resonance imaging (MRI) findings that are similar to the histopathologic lesions that define leukoencephalomyelopathy in Rottweilers. Leukoencephalopathy with brain stem and spinal cord involvement is caused by mutations in the DARS2 gene, which encodes a mitochondrial aspartyl-tRNA synthetase. The objective of this case report is to present the results of MRI and candidate gene analysis of a case of Rottweiler leukoencephalomyelopathy to investigate the hypothesis that leukoencephalomyelopathy in Rottweilers could serve as an animal model of human leukoencephalopathy with brain stem and spinal cord involvement.

Case presentation

A two-and-a-half-year-old male purebred Rottweiler was evaluated for generalised progressive ataxia with hypermetria that was most evident in the thoracic limbs. MRI (T2-weighted) demonstrated well-circumscribed hyperintense signals within both lateral funiculi that extended from the level of the first to the sixth cervical vertebral body. A neurodegenerative disorder was suspected based on the progressive clinical course and MRI findings, and Rottweiler leukoencephalomyelopathy was subsequently confirmed via histopathology. The DARS2 gene was investigated as a causative candidate, but a sequence analysis failed to identify any disease-associated variants in the DNA sequence.

Conclusion

It was concluded that MRI may aid in the pre-mortem diagnosis of suspected cases of leukoencephalomyelopathy. Genes other than DARS2 may be involved in Rottweiler leukoencephalomyelopathy and may also be relevant in human leukoencephalopathy with brain stem and spinal cord involvement.

GM2 gangliosidosis associated with a HEXA missense mutation in Japanese Chin dogs: a potential model for Tay Sachs disease

GM2 gangliosidosis is a fatal lysosomal storage disease caused by a deficiency of β-hexosaminidase (EC 3.2.1.52). There are two major isoforms of the enzyme: hexosaminidase A composed of an α and a β subunit (encoded by HEXA and HEXB genes, respectively); and, hexosaminidase B composed of two β subunits. Hexosaminidase A requires an activator protein encoded by GM2A to catabolize GM2 ganglioside, but even in the absence of the activator protein, it can hydrolyze the synthetic substrates commonly used to assess enzyme activity. GM2 gangliosidosis has been reported in Japanese Chin dogs, and we identified the disease in two related Japanese Chin dogs based on clinical signs, histopathology and elevated brain GM2 gangliosides. As in previous reports, we found normal or elevated hexosaminidase activity when measured with the synthetic substrates. This suggested that the canine disease is analogous to human AB variant of G(M2) gangliosidosis, which results from mutations in GM2A. However, only common neutral single nucleotide polymorphisms were found upon sequence analysis of the canine ortholog of GM2A from the affected Japanese Chins. When the same DNA samples were used to sequence HEXA, we identified a homozygous HEXA:c967G>A transition which predicts a p.E323K substitution. The glutamyl moiety at 323 is known to make an essential contribution to the active site of hexosaminidase A, and none of the 128 normal Japanese Chins and 92 normal dogs of other breeds that we tested was homozygous for HEXA:c967A. Thus it appears that the HEXA:c967G>A transition is responsible for the GM2 gangliosidosis in Japanese Chins.

Neuronal ceroid lipofuscinosis in Border Collie dogs in Japan: clinical and molecular epidemiological study (2000-2011)

Neuronal ceroid lipofuscinosis (NCL) is an inherited, neurodegenerative lysosomal disease that causes premature death. The present study describes the clinical and molecular epidemiologic findings of NCL in Border Collies in Japan for 12 years, between 2000 and 2011. The number of affected dogs was surveyed, and their clinical characteristics were analyzed. In 4 kennels with affected dogs, the dogs were genotyped. The genetic relationships of all affected dogs and carriers identified were analyzed. The survey revealed 27 affected dogs, but there was a decreasing trend at the end of the study period. The clinical characteristics of these affected dogs were updated in detail. The genotyping survey demonstrated a high mutant allele frequency in examined kennels (34.8%). The pedigree analysis demonstrated that all affected dogs and carriers in Japan are related to some presumptive carriers imported from Oceania and having a common ancestor. The current high prevalence in Japan might be due to an overuse of these carriers by breeders without any knowledge of the disease. For NCL control and prevention, it is necessary to examine all breeding dogs, especially in kennels with a high prevalence. Such endeavors will reduce NCL prevalence and may already be contributing to the recent decreasing trend in Japan.

A frameshift mutation in the canine HEXB gene in toy poodles with GM2 gangliosidosis variant 0 (Sandhoff disease)

GM2 gangliosidosis variant 0 (Sandhoff disease, SD) is a fatal, progressive neurodegenerative lysosomal storage disease caused by mutations in the HEXB gene. Toy poodles recently were reported as the second breed of dog with SD. The present paper describes the molecular defect of this canine SD as the first identification of a pathogenic mutation in the canine HEXB gene. Genomic and complementary DNA sequences covering exonic regions of the canine HEXB gene, except exon 1, were analysed using DNA and RNA in an affected dog. A homozygous single base pair deletion of guanine in exon 3 was identified at nucleotide position 283 of the putative open reading frame (c.283delG). This mutation has the potential to cause a frameshift resulting in the alteration of valine at amino acid position 59 to a stop codon (p.V59fsX). Genotyping using the mutagenically separated PCR method demonstrated a correlation between phenotype and genotype in dogs with a pedigree related to the disease and that the mutation was rare in a randomly-selected population of toy poodles. These results strongly suggest that the deletion is pathogenic.

Serial MRI features of canine GM1 gangliosidosis: a possible imaging biomarker for diagnosis and progression of the disease

GM1 gangliosidosis is a fatal neurodegenerative lysosomal storage disease caused by an autosomal recessively inherited deficiency of β-galactosidase activity. Effective therapies need to be developed to treat the disease. In Shiba Inu dogs, one of the canine GM1 gangliosidosis models, neurological signs of the disease, including ataxia, start at approximately 5 months of age and progress until the terminal stage at 12 to 15 months of age. In the present study, serial MR images were taken of an affected dog from a model colony of GM1 gangliosidosis and 4 sporadic clinical cases demonstrating the same mutation in order to characterize the MRI features of this canine GM1 gangliosidosis. By 2 months of age at the latest and persisting until the terminal stage of the disease, the MR findings consistently displayed diffuse hyperintensity in the white matter of the entire cerebrum on T2-weighted images. In addition, brain atrophy manifested at 9 months of age and progressed thereafter. Although a definitive diagnosis depends on biochemical and genetic analyses, these MR characteristics could serve as a diagnostic marker in suspect animals with or without neurological signs. Furthermore, serial changes in MR images could be used as a biomarker to noninvasively monitor the efficacy of newly developed therapeutic strategies.

Rapid and Simple Polymerase Chain Reaction—Based Diagnostic Assays for GM2 Gangliosidosis Variant 0 (Sandhoff-Like Disease) in Japanese Domestic Cats

Polymerase chain reaction (PCR)-based assays combined with microchip electrophoresis were developed and evaluated for diagnosis and genotyping of GM2 gangliosidosis variant 0 (Sandhoff-like disease) in Japanese domestic cats. A preliminary genotyping survey was carried out in the population of Japanese domestic cats (1,015 cats in total) in southern Japan. Three kinds of assays including PCR primer-induced restriction analysis (PIRA) and mutagenically separated (MS)-PCR were carried out using blood-stained Flinders Technology Associates filter papers (FTA cards) as templates. The PCR products were analyzed by both agarose gel and microchip electrophoreses. All assays were sufficient to determine the genotypes of this disease, but MS-PCR offered the most rapid and simplest test, as it does not need the restriction enzyme step required in PCR-PIRA. The use of microchip electrophoresis in combination with FTA cards for sampling could shorten the time required for genotyping and simplify the procedure as well. The genotyping survey in the current study did not find any cats that possessed the mutant allele, suggesting that the prevalence of this allele is low (<0.1%) in southern Japan.