Novel mutations in the FUCA1 gene that cause fucosidosis.

Fucosidosis is a rare lysosomal storage disorder inherited in an autosomal recessive manner. Its estimated frequency is below 1 in 200,000 live births. Its clinical phenotypes include progressive neurological and mental deterioration, coarse facial features, growth retardation, visceromegaly, angiokeratomas, and seizures. The disease is caused by mutations in the FUCA1 gene that lead to deficiency of a-L-fucosidase. Here, we describe the clinical and molecular features of a Thai boy with fucosidosis. Whole exome sequencing and array-based comparative genomic hybridization analysis revealed that the patient was compound heterozygous for a single base-pair deletion (c.670delC; p.P224LfsX2) inherited from his father, and a 3281-base-pair deletion covering exon 3 inherited from his mother. Neither mutation has been reported before so the FUCA1 mutational spectrum is herein expanded.

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.

Myelin genes are downregulated in canine fucosidosis.

The processes regulating the complex neurodegenerative cascade of vacuolation, neuroinflammation, neuronal loss and myelin deficits in fucosidosis, a neurological lysosomal storage disorder, remain unclear. To elucidate these processes the gene expression profile of the cerebral cortex from untreated and intrathecal enzyme replacement therapy treated fucosidosis pups and age-matched unaffected controls were examined. Neuroinflammation and cell death processes were identified to have a major role in fucosidosis pathophysiology with 37% of differentially expressed (DE) genes involved in these processes. Critical, specific, early decreases in expression levels of key genes in myelin assembly were identified by gene expression profiling, including myelin-associated glycoprotein (MAG), myelin and lymphocyte protein (MAL), and oligodendrocyte myelin paranodal and inner loop protein (OPALIN). These gene expression changes may be indicative of early neuronal loss causing reduced electrical impulses required for oligodendrocyte maturation.

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.

A case of chronic infantile type of fucosidosis: clinical and magnetic resonance image findings.

Fucosidosis is a rare autosomal recessive disorder resulting from a deficiency of alpha-L-fucosidase. In this report, we describe clinical and magnetic resonance image (MRI) findings of a chronic infantile type patient heterozygous for a nonsense mutation and a large deletion. The disease onset occurred at 2-3 years of age. She was bound to a wheelchair at 6 years of age, and developed dystonia at the age of 13 years. Brain MRI at 13 years of age showed marked cerebral and cerebellar atrophy, high intensities in the white matter of the frontal and occipital lobes, and low intensities of the bilateral thalamus, striatum, substantia nigra, red nucleus and mamillary bodies on T2-weighted images. The low intensities of basal ganglia on T2-weighted images seems characteristic of lesions in fucosidosis.

Deficiency of fucosidase results in acrosomal dysgenesis and impaired sperm maturation.

Although a variety of glycosyltransferases and glycosidases have been implicated in spermatogenesis and posttesticular sperm maturation, the biological role of these enzymes in these processes is largely unknown. We describe reproductive sequelae in a cohort of male dogs suffering from fucosidosis, a heritable lysosomal storage disorder caused by a severe deficiency of alpha-L-fucosidase. There was a reduction in the total number of sperm in the ejaculate. Only 3-5% of sperm were motile. None of the sperm were found to be morphologically normal. The predominant morphological defects observed were malformed acrosomes (56%) and retained proximal cytoplasmic droplets (92%), indicating that spermiogenesis and sperm maturation were impaired. The cytoplasm of all cellular components of the testis and excurrent ducts were vacuolated. The vacuolation resulted from enlargement of lysosomes caused by accumulation of compounds that are otherwise cleaved/degraded when lysosomal hydrolases are present normally. It is possible that impairment in spermatogenesis, particularly morphogenesis of the acrosome, is due to physical damage caused by anomalous enlargement of lysosomes. Although an unambiguous causal relationship could not be established, it is evident from the available information that the derangement in events associated with epididymal sperm maturation, namely acquisition of motility and shedding of the cytoplasmic droplet, is likely due to lack of fucosidase leading to impaired sperm membrane modification. This heritable condition in dogs may serve as a spontaneously occurring knock-out model for further elucidating the role of alpha-L-fucosidase in spermatogenesis and sperm maturation.

Recurrent respiratory infections in a child with fucosidosis: is the mucus too thin for effective transport?

Fucosidosis is caused by a deficiency of the lysosomal enzyme alpha-L-fucosidase (ALF) leading to an accumulation of glycoproteins in a variety of cells. Infants and young children with this disorder are prone to recurrent sinus and pulmonary infections and often die of pneumonia. We studied the mucociliary and systemic immune function in a 6 year old girl with fucosidosis and recurrent respiratory infections. All measurements of systemic immune function were normal. Sweat chloride was normal when measured on angiokeratotic skin but was greater than 65 mg/L on uninvolved areas. During the placement of tympanic ventilation tubes, tracheal mucus was gently aspirated and a mucosal biopsy was taken. Tracheal mucus transport was not measured. The biopsy material was examined under phase contrast microscopy and revealed ciliated cells with apparently normal beating. TEM of these cells showed a characteristic pattern of vacuoles in the cytoplasm as described in other tissues from patients with fucosidosis. Ciliary ultrastructure was normal. Mucus viscoelasticity was measured in a magnetic microrheometer. The loss tangent was 2 SD above the mean for normal mucus and mechanical impedance was about 2 SD below the mean. These changes are similar in direction but double in magnitude to what has been described with methacholine administration in dogs. The high compliance of the mucus may be due to incomplete assembly of mucus glycoprotein or to decreased secretion of glycoproteins in respiratory secretions. This leads to mucus that is abnormally watery and thus difficult to clear from the airway.

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.