Canine fucosidosis: a biochemical and genetic investigation

Associations between neurologic dysfunction and lesions in canine fucosidosis

Canine fucosidosis in English Springer spaniels is the only animal model of the neurovisceral lysosomal storage disease fucosidosis available for preclinical therapeutic trials. For this reason, it is crucial to identify critical time points in disease progression, and if there are particular lesions associated with specific aspects of neurologic dysfunction. Historical records of 53 canine fucosidosis cases from 1979 to 2009 containing a neurologic dysfunction score assessing motor, behavioral and sensory dysfunction were interrogated by statistical analysis. Motor and behavioral dysfunction scores assessing gait deficits and apprehensive behavior first significantly increased at 12-17 months, and increased at each 6-month interval thereafter. Sensory dysfunction scores, assessing hearing loss, balance and vision deterioration, did not significantly increase until 18-23 months, and coincided with a rapid decline in neurologic function. Regression analysis incorporating published neuropathology data, measured by image analysis, identified neuroinflammation and apoptotic cell death as significant informative predictors of increasing neurologic dysfunction. These findings indicate that the level of neuropathology required to induce consistent and conspicuous clinical signs in canine fucosidosis is reached by approximately 12 months of age in the absence of other disease processes. Significant association between neuroinflammation and apoptotic cell death also suggests that specifically targeting these lesions combined with enzyme replacement in future studies may reduce disease burden in fucosidosis. Overall, examining this historical clinical data to identify associations between the extent of neuropathology and degree of clinical dysfunction provides a useful reference tool for monitoring disease and evaluating therapeutic trials conducted in canine fucosidosis.

Dried blood spots for the enzymatic diagnosis of lysosomal storage diseases in dogs and cats

BACKGROUND

In people, lysosomal storage diseases (LSD) can be diagnosed by assaying enzyme activities in dried blood spots (DBS).

OBJECTIVE

The aim of this study was to evaluate the feasibility of using DBS samples from dogs and cats to measure lysosomal enzymatic activities and diagnose LSD.

METHODS

Drops of fresh whole blood collected in EDTA from dogs and cats with known or suspected LSD and from clinically healthy dogs and cats were placed on neonatal screening cards, dried, and mailed to the Metabolic Laboratory, University Children's Hospital, Frankfurt, Germany. Activities of selected lysosomal enzymes were measured using fluorescent substrates in a 2-mm diameter disk (~2.6 μL blood) punched from the DBS. Results were expressed as nmol substrate hydrolyzed per mL of blood per minute or hour.

RESULTS

Reference values were established for several lysosomal enzyme activities in DBS from dogs and cats; for most enzymes, activities were higher than those published for human samples. Activities of β-glucuronidase, N-acetylglucosamine-4-sulfatase (arylsulfatase B), α-mannosidase, α-galactosidase, α-fucosidase, and hexosaminidase A were measureable in DBS from healthy cats and dogs; α-iduronidase activity was measureable only in cats. In samples from animals with LSD, markedly reduced activity of a specific enzyme was found. In contrast, in samples from cats affected with mucolipidosis II, activities of lysosomal enzymes were markedly increased.

CONCLUSIONS

Measurement of lysosomal enzyme activities in DBS provides an inexpensive, simple, and convenient method to screen animals for suspected LSD and requires only a small sample volume. For diseases in which the relevant enzyme activity can be measured in DBS, a specific diagnosis can be made.

Treatment of canine fucosidosis by intracisternal enzyme infusion

The blood brain barrier is the major obstacle to treating lysosomal storage disorders of the central nervous system such as canine fucosidosis. This barrier was overcome by three, monthly injections of recombinant canine α-l-fucosidase enzyme were given intracisternally. In dogs treated from 8 weeks of age enzyme reached all areas of central nervous system as well as the cervical lymph node, bone marrow and liver. Brainstem and spinal cord samples from regions adjacent to the injection site had highest enzyme levels (39-73% of normal). Substantial enzyme activity (8.5-20% of normal controls) was found in the superficial brain compared to deeper regions (2.6-5.5% of normal). Treatment significantly reduced the fucosyl-linked oligosaccharide accumulation in most areas of CNS, liver and lymph node. In the surface and deep areas of lumbar spinal cord, oligosaccharide accumulation was corrected (79-80% reduction) to near normal levels (p<0.05). In the spinal meninges (thoracic and lumbar) enzyme activity (35-39% of normal control) and substrate reduction (58-63% affected vehicle treated samples) reached levels similar to those seen in phenotypically normal carriers (p<0.05).The procedure was safe and well-tolerated, treated (average 16%) dogs gained more weight (p<0.05) and there was no antibody formation or inflammatory reaction in plasma and CSF following treatments. The capacity of early ERT to modify progression of biochemical storage in fucosidosis is promising as this disease is currently only amenable to treatment by bone marrow transplantation which entails unacceptably high risks for many patients.

Canine fucosidosis: a neuroprogressive disorder

The lysosomal storage disease, canine fucosidosis, is caused by the absence of the lysosomal enzyme canine α-L-fucosidase with storage of undegraded fucose-rich material in different organs. Canine fucosidosis is a severe, progressive, fatal neurological disease which results in death or euthanasia and is the only available animal model for this human disease. We analysed the progressive neuropathology from birth to severe clinical disease and related this to the clinical signs. At birth no vacuolation was observed in fucosidosis brain; however, a complex storage presence with vacuolation was well established by 4 months of age, before the clinical signs of motor dysfunction which occurred at 10-12 months of age. Purkinje cell loss, neuronal loss, gliosis, perivascular storage and demyelination accompanied disease progression. Increased vacuolation (15.3-fold increase compared to controls) coincided with advanced motor and mental deterioration in late-stage disease. Significant loss of myelin commenced early, with greatest impact in the cerebellum, and was severe in late disease (1.6- to 1.9-fold decrease) compared to controls (p < 0.05) contributing to clinical signs of motor and mental dysfunction. This detailed description and quantification of the CNS pathology in canine fucosidosis will inform monitoring of the onset, progression and response of this disease to therapy.

Inherited metabolic disease in companion animals: searching for nature's mistakes

Inborn errors of metabolism are caused by genetic defects in intermediary metabolic pathways. Although long considered to be the domain of human paediatric medicine, they are also recognised with increasing frequency in companion animals. The diagnosis of diseased animals can be achieved by searching for abnormal metabolites in body fluids, although such screening programmes have, until now, not been widely available to the small animal clinician. A comprehensive battery of analytical tools exists for screening for inborn metabolic diseases in humans which can be applied to animals and serve not only for the diagnosis of affected patients but also to detect asymptomatic carriers and further our understanding of metabolic pathways in dogs and cats. Moreover, naturally occurring animal models of inherited metabolic diseases provide a unique opportunity to study the biochemical and molecular pathogenesis of these disorders and to investigate possible therapeutic options.

Lysosomal storage diseases of animals: an essay in comparative pathology

A wide variety of inherited lysosomal hydrolase deficiencies have been reported in animals and are characterized by accumulation of sphingolipids, glycolipids, oligosaccharides, or mucopolysaccharides within lysosomes. Inhibitors of a lysosomal hydrolase, e.g., swainsonine, may also induce storage disease. Another group of lysosomal storage diseases, the ceroid-lipofuscinoses, involve the accumulation of hydrophobic proteins, but their pathogenesis is unclear. Some of these diseases are of veterinary importance, and those caused by a hydrolase deficiency can be controlled by detection of heterozygotes through the gene dosage phenomenon or by molecular genetic techniques. Other of these diseases are important to biomedical research either as models of the analogous human disease and/or through their ability to help elucidate specific aspects of cell biology. Some of these models have been used to explore possible therapeutic strategies and to define their limitations and expectations.

A new form of ovine GM1-gangliosidosis

Neurological signs were observed in 3 lambs at approximately 1 month of age, in a flock of 1 ram and 29 ewes with 43 lambs. Deterioration occurred such that the lambs had either died or been killed by 4 months of age. Necropsies of two of these lambs revealed a diffuse encephalopathy in which the most prominent feature was ballooned neurons. Sections of frozen brain showed PAS-positive, oil red O-negative, and weak Sudan Black-positive material in the swollen neuronal cytoplasm. The ultrastructure of the neuronal inclusions showed characteristic whorled membranes, suggesting diagnosis of a gangliosidosis. The underlying enzymic defect was investigated by assaying 11 lysosomal enzymes in extracts of kidney from an affected lamb and from normal lambs. A deficiency (90%) of acidic beta-D-galactosidase was found in the affected lamb. All other activities, including N-acetylneuraminidase, were normal. A specific deficiency of lysosomal beta-D-galactosidase was demonstrated by separating the lysosomal and cytosolic beta-D-galactosidase by chromatography on concanavalin A-Sepharose. Diagnosis of GM1-gangliosidosis, analogous to the severe infantile form of the human disease, was made on the basis of the pathology and enzymology. The beta-D-galactosidase activity in the white blood cells of the ram and several of the ewes was consistent with their being heterozygotes. This disorder is different from a previously described lipidosis in sheep, in which there was a combined deficiency of beta-D-galactosidase and alpha-neuraminidase.

Amelioration of clinical disease following bone marrow transplantation in fucosidase-deficient dogs

Canine fucosidosis was studied as an animal model for the treatment of neurovisceral lysosomal storage disease. Following successful bone marrow engraftment, dogs with fucosidosis had increased levels of alpha-L-fucosidase enzyme activity in leukocytes, plasma, and neural and visceral tissues. This widespread increase in enzyme activity was accompanied by a rapid improvement in the peripheral nerve and visceral lesions of fucosidosis and a more gradual improvement in the central nervous system pathology. Long-term engraftment from an early age reduced the severity and slowed the progression of clinical neurological disease. Transplantation after the onset of clinical signs was not effective. These findings suggest that the neurological damage caused by some inherited metabolic disorders, such as fucosidosis, may be preventable but emphasise the need for early diagnosis and treatment.

Fucosidosis revisited: a review of 77 patients

Fucosidosis is a rare, autosomal recessive, lysosomal storage disorder caused by a severe deficiency of alpha-L-fucosidase in all tissues. We have conducted a review of fucosidosis, compiling data from published reports and an international questionnaire survey. Seventy-seven patients affected with fucosidosis of which 19 had not been reported before have been identified. A major aim of the present study was to define the natural history of fucosidosis. The clinical picture of fucosidosis consists of progressive mental (95%) and motor (87%) deterioration, coarse facies (79%), growth retardation (78%), recurrent infections (78%), dysostosis multiplex (58%), angiokeratoma corporis diffusum (52%), visceromegaly (44%), and seizures (38%). Whereas the original fucosidosis patients described by Durand et al. (J. Pediatr 75:665-674, 1969) were decerebrate and died before age 5 years, most fucosidosis patients have a slower course of degeneration. Mortality before age 5 years was observed in only 7 patients (9%), whereas 36 patients (64%) reached the second decade. We did not find evidence for the existence of clinical heterogeneity with a rapidly progressive type I and a slowly progressive type II fucosidosis as suggested in the literature. Instead, there seems to exist a wide continuous clinical spectrum. At the biochemical level no heterogeneity in residual fucosidase enzyme activity or cross-reacting immunoreactive fucosidase protein was observed. At the DNA level at least 4 different mutations must be responsible for fucosidosis. These genotypic differences however do not explain the observed phenotypic differences.

Reproductive abnormalities in canine fucosidosis

Male English springer spaniel dogs affected with fucosidosis, a lysosomal storage disorder, were found to be infertile while females with the disease reproduced successfully. Ejaculates of semen collected from affected dogs had reduced total sperm output and morphologically abnormal spermatozoa. A high proportion of ejaculated spermatozoa had midpiece droplets, bent tails and poor motility. Severely vacuolated epididymal epithelial cells were observed by light microscopy. Electron microscopic examination revealed membrane-bound vacuoles of variable size containing scanty amounts of granular to fibrillar material in epididymal epithelial cells, smooth muscle, myoid cells and Sertoli cells. Male infertility is believed to result from lysosomal storage of fucosyl-linked substrates in cells of the reproductive system. The extensive lesions in the epididymis may have interfered with maturation and transport of spermatozoa. Also, deficiency of alpha-L-fucosidase activity could have impaired the shedding of cytoplasmic droplets from spermatozoa and altered the surface glycoprotein composition of the sperm during epididymal transit.

Enzyme replacement in nervous tissue after allogeneic bone-marrow transplantation for fucosidosis in dogs

Bone-marrow transplantation after total lymphoid irradiation in an alpha-L-fucosidase-deficient dog raised the enzyme activity in both visceral and neural tissues with consequent reduction in the severity of storage lesions. These results offer hope that early marrow transplantation may prevent the development of disease in neurovisceral storage disorders.

Fucosidosis in an English springer spaniel presenting as a malabsorption syndrome

A case of alpha-fucosidosis in a 2-year-old male English Springer Spaniel presented as a malabsorption syndrome without any clinical neurological abnormalities. The dog had a history of chronic weight loss, diarrhoea, mild anaemia, hypoproteinemia and reduced jejunal absorption of D-xylose. A diagnosis of fucosidosis with intestinal malabsorption was based on these findings, markedly reduced plasma fucosidase levels and the diffuse infiltration of the lamina propria and submucosa of the stomach, small intestine, Peyer's patches and mesenteric lymph nodes by macrophages with finely vacuolated cytoplasm. Cytoplasmic vacuolation was also a feature of cells of the pancreas, thryroid, parathyroid and adenohypophysis and the epithelia lining respiratory airways and the urogenital tract. Neurons of the autonomic plexuses of the gastrointestinal tract and the urinary bladder as well as those of the brain, spinal cord, spinal ganglia and retina were also vacuolated. The profound decrease in sigma-fucosidase activity in the brain, liver and kidney was accompanied by a marked increase in 6 other lysosomal enzymes, especially beta-n-acetyl glucosaminidase.