GM1-gangliosidosis in American black bears: Clinical, pathological, biochemical and molecular genetic characterization

https://doi.org/10.1016/j.ymgme.2014.02.002Get rights and content

Highlights

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    Seven young Black Bears found in New England with neurologic symptomatology are investigated.

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    Neurons are swollen with cytoplasmic vacuoles and electron-dense lamellated material.

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    Acid β-galactosidase deficiency and GM1-ganglioside accumulation confirm GM1-gangliosidosis.

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    Brain lipid composition of GM1-mouse and GM1-bear are compared.

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    A missense mutation in exon 10 of the bear GLB1 gene is the cause of this inborn error of metabolism.

Abstract

GM1-gangliosidosis is a rare progressive neurodegenerative disorder due to an autosomal recessively inherited deficiency of lysosomal β-galactosidase. We have identified seven American black bears (Ursus americanus) found in the Northeast United States suffering from GM1-gangliosidosis. This report describes the clinical features, brain MRI, and morphologic, biochemical and molecular genetic findings in the affected bears. Brain lipids were compared with those in the brain of a GM1-mouse. The bears presented at ages 10–14 months in poor clinical condition, lethargic, tremulous and ataxic. They continued to decline and were humanely euthanized. The T2-weighted MR images of the brain of one bear disclosed white matter hyperintensity. Morphological studies of the brain from five of the bears revealed enlarged neurons with foamy cytoplasm containing granules. Axonal spheroids were present in white matter. Electron microscopic examination revealed lamellated membrane structures within neurons. Cytoplasmic vacuoles were found in the liver, kidneys and chondrocytes and foamy macrophages within the lungs. Acid β-galactosidase activity in cultured skin fibroblasts was only 1–2% of control values. In the brain, ganglioside-bound sialic acid was increased more than 2-fold with GM1-ganglioside predominating. GA1 content was also increased whereas cerebrosides and sulfatides were markedly decreased. The distribution of gangliosides was similar to that in the GM1-mouse brain, but the loss of myelin lipids was greater in the brain of the affected bear than in the brain of the GM1 mouse. Isolated full-length cDNA of the black bear GLB1 gene revealed 86% homology to its human counterpart in nucleotide sequence and 82% in amino acid sequence. GLB1 cDNA from liver tissue of an affected bear contained a homozygous recessive T1042 to C transition inducing a Tyr348 to His mutation (Y348H) within a highly conserved region of the GLB1 gene. The coincidence of several black bears with GM1-gangliosidosis in the same geographic area suggests increased frequency of a founder mutation in this animal population.

Introduction

GM1-gangliosidosis is a lysosomal storage disease caused by deficient activity of lysosomal β-galactosidase and subsequent storage of GM1-ganglioside. The enzyme β-galactosidase cleaves the terminal β-galactosyl moiety from GM1-ganglioside, glycoproteins and keratan sulfate [1]. Deficiency of β-galactosidase is transmitted as an autosomal recessive trait. It results in storage of GM1-ganglioside in neural tissue, oligosaccharides in different tissues and keratan sulfate in various mesenchymal cells such as fibroblasts and cartilage. It occurs in humans and has been found as well in domestic animals including different breeds of dogs and cats and in cattle, sheep [2] and emus [3]. We report here the clinical, morphological, biochemical and molecular genetic findings in GM1-gangliosidosis in seven free-ranging American black bears (Ursus americanus) from New England.

Section snippets

History and clinical presentations

Within the past five years, five American black bears have been necropsied at Tufts University Cummings School of Veterinary Medicine in Grafton, MA. They include three males and two females of ages 10 to 14 months old. The bears were from Massachusetts and New Hampshire. Clinical examinations showed that these bears were lethargic, severely dehydrated and in poor body condition. They had intention tremors of the head as well as whole body tremors, generalized ataxia and thoracic limb

Pathology

Venous blood samples from two bears were collected in EDTA and from them, smears were prepared and stained with Wright–Giemsa. A head MRI examination was performed on a 14-month-old female. The necropsy of a 13-month-old male bear performed at the Veterinary Diagnostic Laboratory at the University of Maine revealed diffusely congested lungs with a small amount of brown mucoid exudate in the trachea. Necropsies of five other bears were done at Tufts University Cummings School of Veterinary

Morphological findings

Blood smears revealed a few vacuolated mononuclear cells and neutrophils. The most prominent morphological changes were noted in the nervous system. Pathological examination of the brain revealed variable atrophy with mild prominence of sulci and ventricles. (Fig. 2A). Hematoxylin and eosin-stained sections of the brain and peripheral ganglia contained enlarged neurons with foamy cytoplasm. In neurons of some regions of the brain including the retina the cytoplasm contained numerous small

Discussion

In this report we describe the storage of GM1-ganglioside in wild black bears from four New England states. The neurological, morphological and biochemical findings, i.e. storage of GM1-ganglioside in the neurons of these wild black bears are similar in part to those observed in other species [1], [3], [6], [12], [13], [14], [15]. Abnormal myelination was noted in the female bear both by MRI and by histology and is reflected in the marked loss of brain myelin lipids, cerebrosides and

Acknowledgments

This study was supported in part by the Margaret Enoch Fund in the Department of Neurology at the NYU School of Medicine and grants to TNF by the NIH (NS055195) and the Boston College Research Expense Fund.

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