Refractory congenital ascites as a manifestation of neonatal sialidosis: clinical, biochemical and morphological studies in a newborn Syrian male infant

A Syrian newborn with coarse facies, hepato-splenomegaly, and refractory ascites is reported. Examination of the ascitic fluid showed vacuolated lymphocytes and thin-layer chromatography of urinary oligosaccharides revealed an abnormal pattern indicative of sialidosis. Despite intensive care, the baby died of respiratory insufficiency 28 days after birth. In cultured skin fibroblasts an increase of the incorporation of [14C]methylamine pointed to excessive lysosomal storage and the demonstration of an isolated deficiency of alpha-N-acetylneuraminidase (sialidase) led to the diagnosis of a sialidosis. At postmortem examination, foam cells were found mostly in bone marrow, liver, and brain. To date very few cases of neonatal sialidosis have been reported, and, to the best of our knowledge, this is the first child with neonatal sialidosis from Syria and the first case of neonatal sialidosis studied by the [14C]methylamine incorporation assay.

Lipoid proteinosis. A biochemical and ultrastructural investigation of two new cases

Lipoid proteinosis is a rare autosomal recessive disease characterized by cutaneous and visceral lesions, in which large amounts of amorphous material are constantly found in stroma. Morphological and biochemical studies indicate abnormal collagen production, but little attention has been paid to the lipid component of lesions. Microscopic and ultrastructural studies of skin, with special emphasis on fibroblasts, vessels, nerve endings and eccrine sweat glands, were conducted in two patients with lipoid proteinosis. Biochemical studies were undertaken in cultured fibroblasts. Evidence of lysosomal storage in epithelial cells of eccrine sweat glands and in dermal histiocytes, very similar to that found in some metabolic disorders, particularly Farber disease, was found in both cases. Our findings suggest that two alterations might coexist in lipoid proteinosis, one characterized by impaired normal collagen production and the other related to a metabolic defect which may lead to accumulation of ceramide or more complex lipids.

Early-infantile galactosialidosis: prenatal presentation and postnatal follow-up

Galactosialidosis (GS) is an autosomal recessive condition caused by combined deficiency of the lysosomal enzymes beta-galactosidase and alpha-neuraminidase. The combined deficiency has been found to result from a defect in protective protein/cathepsin A (PPCA), an intralysosomal protein which protects these enzymes from premature proteolytic processing. The most severe form of GS, the early-infantile form, results in early onset of edema, ascites, visceromegaly, and skeletal dysplasia. We report a case of early-infantile GS in a male infant who presented with nonimmune fetal hydrops (NIH), "coarse" facial appearance, massive fluid-filled inguinal hernias, multiple telangiectasia, and diffuse hypopigmentation; he subsequently developed visceromegaly. The diagnosis of GS was confirmed biochemically and the defect in PPCA characterized at the protein level. Examination of fetal peripheral blood smears sampled at 30 weeks gestation demonstrated vacuolation of lymphocytes, suggesting blood film examination may be a useful screening tool for cases of NIH where a metabolic disorder is suspected. Skeletal radiography at birth demonstrated punctate epiphyses of the femora, calcanei, and sacrum. We present a discussion of and differential diagnosis for this radiographic finding. To the best of our knowledge, this is the first case of early-infantile GS presenting with stippled epiphyses.

A new metabolite contributing to N-acetyl signal in 1H MRS of the brain in Salla disease

OBJECTIVE

To determine whether N-acetylaspartate (NAA) is reduced in patients with Salla disease, a neurodegenerative disorder.

BACKGROUND

1H MRS allows the brain metabolism to be studied noninvasively in vivo. N-acetyl (NA) is composed primarily of NAA, which is regarded as a neuronal marker. The NA signal in 1H MRS is reduced in several neurodegenerative disorders. Increased NA signal has thus far only been found in Canavan's disease as a result of NAA accumulation in the brain tissue. In Salla disease, an autosomal recessive free sialic acid storage disorder, N-acetylneuraminic acid (NANA), accumulates in lysosomes of brain tissue.

METHODS

The authors studied eight patients with Salla disease (age range, 6 to 44 years) and eight age-matched healthy volunteers using quantitative 1H MRS. The spectra were obtained from two selected 8-cm3 volumes of interest localized in the basal ganglia and in the parietal white matter using conventional 1.5-T MRI equipment. The spectral resonance lines of NA groups, creatine and phosphocreatine (Cr), and choline-containing compounds (Cho) were analyzed quantitatively. All MR images were evaluated to verify the state of myelination.

RESULTS

1H MRS from parietal white matter revealed 34% higher NA and 47% higher Cr concentrations, and a 35% lower Cho concentration in the patients with Salla disease compared with the age-matched control subjects. The patients had a 22% higher water content in their parietal white matter, whereas in the basal ganglia the water concentrations did not differ significantly. In the patients' basal ganglia the Cr concentration was 53% higher.

CONCLUSIONS

NAA is considered to be a neuronal marker that, except for Canavan's disease, has been found or assumed to be either stable or reduced. However, in Salla disease the high NA signal may have a contribution from accumulated lysosomal NANA, which offsets the possible loss of NAA. The high Cr is in line with the increased glucose uptake found in our earlier 2-fluoro-2-deoxy-D-glucose-PET study, reflecting increased energy demand. It is worth noting that in a conventional 1H MRS ratio-based analysis these underlying abnormalities would have remained undetected. Our study thus emphasizes the importance of a quantitative assessment of metabolite concentrations in 1H MRS for detecting altered brain metabolism.

Overgrowth of oral mucosa and facial skin, a novel feature of aspartylglucosaminuria

Aspartylglucosaminuria (AGU) is a lysosomal storage disorder caused by deficiency of aspartylglucosaminidase (AGA). The main symptom is progressive mental retardation. A spectrum of different mutations has been reported in this disease, one missense mutation (Cys163Ser) being responsible for the majority of Finnish cases. We were able to examine 66 Finnish AGU patients for changes in the oral mucosa and 44 of these for changes in facial skin. Biopsy specimens of 16 oral lesions, 12 of them associated with the teeth, plus two facial lesions were studied histologically. Immunohistochemical staining for AGA was performed on 15 oral specimens. Skin was seborrhoeic in adolescent and adult patients, with erythema of the facial skin already common in childhood. Of 44 patients, nine (20%) had facial angiofibromas, tumours primarily occurring in association with tuberous sclerosis. Oedemic buccal mucosa (leucoedema) and gingival overgrowths were more frequent in AGU patients than in controls (p<0.001). Of 16 oral mucosal lesions studied histologically, 15 represented fibroepithelial or epithelial hyperplasias and were reactive in nature. Cytoplasmic vacuolisation was evident in four. Immunohistochemically, expression of AGA in AGU patients' mucosal lesions did not differ from that seen in corresponding lesions of normal subjects. Thus, the high frequency of mucosal overgrowth in AGU patients does not appear to be directly associated with lysosomal storage or with alterations in the level of AGA expression.

A lysosomal storage disease induced by Ipomoea carnea in goats in Mozambique

A novel plant-induced lysosomal storage disease was observed in goats from a village in Mozambique. Affected animals were ataxic, with head tremors and nystagmus. Because of a lack of suitable feed, the animals consumed an exotic hedge plant growing in the village that was identified as Ipomoea carnea (shrubby morning glory, Convolvulaceae). The toxicosis was reproduced by feeding I. carnea plant material to goats. In acute cases, histologic changes in the brain and spinal cord comprised widespread cytoplasmic vacuolation of neurons and glial cells in association with axonal spheroid formation. Ultrastructurally, cytoplasmic storage vacuoles in neurons were membrane bound and consistent with lysosomes. Cytoplasmic vacuolation was also found in neurons in the submucosal and mesenteric plexuses in the small intestine, in renal tubular epithelial cells, and in macrophage-phagocytic cells in the spleen and lymph nodes in acute cases. Residual alterations in the brain in chronic cases revealed predominantly cerebellar lesions characterized by loss of Purkinje neurons and gliosis of the Purkinje cell layer. Analysis of I. carnea plant material by gas chromatography-mass spectrometry established the presence of the mannosidase inhibitor swainsonine and 2 glycosidase inhibitors, calystegine B2 and calystegine C1, consistent with a plant-induced alpha-mannosidosis in the goats. The described storage disorder is analogous to the lysosomal storage diseases induced by ingestion of locoweeds (Astragalus and Oxytropis) and poison peas (Swainsona).

Neonatal gene transfer leads to widespread correction of pathology in a murine model of lysosomal storage disease

For many inborn errors of metabolism, early treatment is critical to prevent long-term developmental sequelae. We have used a gene-therapy approach to demonstrate this concept in a murine model of mucopolysaccharidosis type VII (MPS VII). Newborn MPS VII mice received a single intravenous injection with 5.4 x 10(6) infectious units of recombinant adeno-associated virus encoding the human beta-glucuronidase (GUSB) cDNA. Therapeutic levels of GUSB expression were achieved by 1 week of age in liver, heart, lung, spleen, kidney, brain, and retina. GUSB expression persisted in most organs for the 16-week duration of the study at levels sufficient to either reduce or prevent completely lysosomal storage. Of particular significance, neurons, microglia, and meninges of the central nervous system were virtually cleared of disease. In addition, neonatal treatment of MPS VII mice provided access to the central nervous system via an intravenous route, avoiding a more invasive procedure later in life. These data suggest that gene transfer mediated by adeno-associated virus can achieve therapeutically relevant levels of enzyme very early in life and that the rapid growth and differentiation of tissues does not limit long-term expression.

Expression of protective protein in human tissue

The authors investigated by immunohistochemistry the distribution of protective protein in human tissues. Immunoreactivity was observed in the cytoplasm, revealing a granular pattern and cell type specificity. The most intense staining was observed in the large neurons of brain, distal and collecting tubular cells of kidney, epithelial cells of bronchus, and Leydig cells of testis. In a patient with galactosialidosis type IIa, all these stains were absent. The neurons that were most strongly stained in the control group, such as the Betz cells, neurons in the basal forebrain, motor neurons in the cranial nerve nuclei, and ventral horn cells of the spinal cord, were markedly ballooned in the patient with galactosialidosis.

Brain involvement in Salla disease

BACKGROUND AND PURPOSE

Our purpose was to document the nature and progression of brain abnormalities in Salla disease, a lysosomal storage disorder, with MR imaging.

METHODS

Fifteen patients aged 1 month to 43 years underwent 26 brain MR examinations. In 10 examinations, signal intensity was measured and compared with that of healthy volunteers of comparable ages.

RESULTS

MR images of a 1-month-old asymptomatic child showed no pathology. In all other patients, abnormal signal intensity was found: on T2-weighted images, the cerebral white matter had a higher signal intensity than the gray matter, except in the internal capsules. In six patients, the white matter was homogeneous on all images. In four patients, the periventricular white matter showed a somewhat lower signal intensity; in five patients, a higher signal intensity. In the peripheral cerebral white matter, the measured signal intensity remained at a high level throughout life. No abnormalities were seen in the cerebellar white matter. Atrophic changes, if present, were relatively mild but were found even in the cerebellum and brain stem. The corpus callosum was always thin.

CONCLUSION

In Salla disease, the cerebral myelination process is defective. In some patients, a centrifugally progressive destructive process is also seen in the cerebral white matter. Better myelination in seen in patients with milder clinical symptoms.

Clinical spectrum of infantile free sialic acid storage disease

Infantile free sialic acid storage disease (ISSD) is a rare autosomal recessive metabolic disorder caused by a lysosomal membrane transport defect, resulting in accumulation of free sialic acid within lysosomes. Only a few cases have been described. We report on three new cases of ISSD with different modes of presentation: an infant with nephrotic syndrome, a case of fetal and neonatal ascites with heart failure, and a case of fetal ascites with esophageal atresia type III. From these patients and a review of the literature (27 cases total) we draw the following conclusions. 1) "Coarse facies," fair complexion, hepatosplenomegaly, and severe psychomotor retardation are constant findings in this disorder. 2) Nephrotic syndrome occurred in most cases (four in seven) in which renal evaluation was performed. Therefore, ISSD is an important cause of nephrosis in infants with a storage disorder phenotype. 3) Fetal/neonatal ascites or hydrops was the mode of presentation in 13 (60%) of 21 cases. Thus, ISSD enters in the differential diagnosis of hydrops fetalis with a storage disease phenotype. 4) Cardiomegaly was evident in nine cases. 5) Corneae were always clear, and albinoid fundi were reported in five cases. 6) Dysostosis multiplex was not prominent. 7) Bone marrow aspiration could be negative. 8) Death ensued in early infancy with a mean age of 13.1 months. All reported deaths were caused by respiratory infections.

Increased brain glucose utilization in Salla disease (free sialic acid storage disorder)

Salla disease is an autosomal recessive lysosomal free sialic acid storage disorder characterized by psychomotor retardation and ataxia. MRI studies have revealed evidence of dysmyelination, but the biological mechanism of the brain dysfunction is unknown.

METHODS

Nine patients with Salla disease (age 2.5 mo-42 y) presenting the disease in varying degrees of severity were studied by PET using 2-fluoro-2-deoxy-D-glucose (FDG) as a tracer. Local cerebral metabolic rates for glucose (LCMRGlc) in individual brain regions were compared with controls.

RESULTS

The FDG PET results showed significantly increased LCMRGlc values in the frontal and sensorimotor cortex and especially in the basal ganglia of the patients. Cerebellar hypometabolism was present in all seven patients with marked ataxia, whereas the less severely affected patients without obvious ataxia had normal or even high glucose uptake in the cerebellum.

CONCLUSION

The increased cerebral glucose utilization is a constant finding in Salla disease and may reflect the basic defect of the sialic acid metabolism in this disorder. The FDG PET findings in the cerebellum suggest a correlation between glucose uptake and the severity of the clinical symptoms.

Application of magnetic chromatography to the isolation of lysosomes from fibroblasts of patients with lysosomal storage disorders

A method for the purification of lysosomes from fibroblasts has been developed which uses endocytosis of superparamagnetic colloidal iron dextran particles followed by separation of the iron-containing lysosomes in a magnetic field. This permitted isolation of lysosomes from fibroblasts from patients with infantile sialic acid storage disorder and other lysosomal storage diseases in which a shift in lysosomal density induced by the storage material prevents purification by centrifugation in a Percoll gradient. The magnetic lysosomes isolated from these cells are very similar to those from normal cells as judged by lysosomal marker enzyme activity and 2D-PAGE analysis of the enriched proteins.

Mature monocytic cells enter tissues and engraft

The goal of this study was to identify the circulating cell that is the immediate precursor of tissue macrophages. ROSA 26 marrow mononuclear cells (containing the beta-geo transgene that encodes beta-galactosidase and neomycin resistance activities) were cultured in the presence of macrophage colony-stimulating factor and flt3 Ligand for 6 days to generate monocytic cells at all stages of maturation. Expanded monocyte cells (EMC), the immature (ER-MP12(+)) and more mature (ER-MP20(+)) subpopulations, were transplanted into irradiated B6/129 F2 mice. beta-gal staining of tissue sections from animals 15 min after transplantation demonstrated that the donor cells landed randomly. By 3 h, donor cells in lung and liver were more frequent in animals transplanted with ER-MP20(+) (more mature) EMC than in animals transplanted with unseparated EMC or fresh marrow mononuclear cells, a pattern that persisted at 3 and 7 days. At 3 days, donor cells were found in spleen, liver, lung, and brain (rarely) as clusters as well as individual cells. By 7 and 14 days, the clusters had increased in size, and the cells expressed the macrophage antigen F4/80, suggesting that further replication and differentiation had occurred. PCR for the neogene was used to quantitate the amount of donor DNA in tissues from transplanted animals and confirmed that ER-MP20(+) EMC preferentially engrafted. These data demonstrate that a mature monocytic cell gives rise to tissue macrophages. Because these cells can be expanded and manipulated in vitro, they may be a suitable target population for gene therapy of lysosomal storage diseases.

Lysosomal glycogen storage disease with normal acid maltase with early fatal outcome

In a male infant who had cardiomyopathy, generalized muscle weakness and increased serum creatine kinase levels, his muscle biopsy revealed myopathic changes with tiny intracytoplasmic vacuoles containing PAS-positive material and high acid phosphatase activity, but had normal acid maltase activity biochemically. These findings were consistent with those seen in lysosomal glycogen storage disease with normal acid maltase (Danon disease). Sarcolemmal indentations commonly seen in this disease were missing, but a complement membrane attack complex, C5b-9 was positive along the surface membrane of the muscle fibers as seen in X-linked vacuolar myopathy. The patient was on a respirator and died at 27 months of age from pneumonia and hypertrophic cardiomyopathy. Lysosomal glycogen storage disease with normal acid maltase may be manifested at birth with marked skeletal and cardiac involvement leading to death in early infancy.

Adenovirus-mediated gene transfer results in decreased lysosomal storage in brain and total correction in liver of aspartylglucosaminuria (AGU) mouse

Aspartylglucosaminuria (AGU) is a lysosomal storage disease leading to mental retardation, which is caused by deficiency of aspartylglucosaminidase (AGA). AGU is strongly enriched in the Finnish population in which one major mutation called AGU(Fin) has been identified. The molecular pathogenesis of AGU as well as the biology of the AGA enzyme have been extensively studied, thus giving a profound basis for therapeutic interventions. In this study we have performed adenovirus-mediated gene transfer to the recently produced mouse model of AGU, which exhibits similar pathophysiology as that in humans. Recombinant adenovirus vectors encoding for the human AGA and AGU(Fin) polypeptides were first applied in primary neurons of AGU mouse to demonstrate wild-type and mutant AGA expression in vitro. In vivo, both of the adenovirus vectors were injected into the tail vein of AGU mice and the expression of AGA was demonstrated in the liver. The adenovirus vectors were also injected intraventricularly into the brain of AGU mice resulting in AGA expression in the ependymal cells lining the ventricles and further, diffusion of AGA into the neighbouring neurons. Also, AGA enzyme injected intraventricularly was shown to transfer across the ependymal cell layer. One month after administration of the wild-type Ad-AGA, a total correction of lysosomal storage in the liver and a partial correction in brain tissue surrounding the ventricles was observed. After administration of the Ad-AGU virus the lysosomal storage vacuoles in liver or brain remained unchanged. These data demonstrate that the lysosomal storage in AGU can be biologically corrected and furthermore, in the brain a limited number of transduced cells can distribute AGA enzyme to the surrounding areas.

Lack of PPCA expression only partially coincides with lysosomal storage in galactosialidosis mice: indirect evidence for spatial requirement of the catalytic rather than the protective function of PPCA

Protective protein/cathepsin A (PPCA) is a pleiotropic lysosomal enzyme that complexes with beta-galactosidase and neuraminidase, and possesses serine carboxypeptidase activity. Its deficiency in man results in the neurodegenerative lysosomal storage disorder galactosialidosis (GS). The mouse model of this disease resembles the human early onset phenotype and results in severe nephropathy and ataxia. To understand better the pathophysiology of the disease, we compared the occurrence of lysosomal PPCA mRNA and protein in normal adult mouse tissues with the incidence of lysosomal storage in PPCA(-/-) mice. PPCA expression was markedly variable among different tissues. Most sites that produced both mRNA and protein at high levels in normal mice showed extensive and overt storage in the knockout mice. However, this correlation was not consistent as some cells that normally expressed high levels of PPCA were unaffected in their storage capability in the PPCA(-/-) mice. In addition, some normally low expressing cells accumulated large amounts of undegraded products in the GS mouse. This apparent discrepancy may reflect a requirement for the catalytic rather than the protective function of PPCA and/or the presence of cell-specific substrates in certain cell types. A detailed map showing the cellular distribution of PPCA in nomal mouse tissues as well as the sites of lysosomal storage in deficient mice is critical for accurate assessment of the effects of therapeutic interventions.

Progressive neurodegeneration in aspartylglycosaminuria mice

Aspartylglycosaminuria (AGU) is one of the most common lysosomal storage disorders in humans. A mouse model for AGU has been recently generated through targeted disruption of the glycosylasparaginase gene, and at a young age the glycosyl asparaginase-deficient mice demonstrated many pathological changes found in human AGU patients (Kaartinen V, Mononen I, Voncken J-W, Gonzalez-Gomez I, Heisterkamp N, Groffen J: A mouse model for aspartylglycosaminuria. Nat Med 1996, 2:1375-1378). Our current findings demonstrate that after the age of 10 months, the general condition of null mutant mice gradually deteriorated. They suffered from a progressive motoric impairment and impaired bladder function and died prematurely. A widespread lysosomal hypertrophy in the central nervous system was detected. This neuronal vacuolation was particularly severe in the lateral thalamic nuclei, medullary reticular nuclei, vestibular nuclei, inferior olivary complex, and deep cerebellar nuclei. The oldest animals (20 months old) displayed a clear neuronal loss and gliosis, particularly in those regions, where the most severe vacuolation was found. The severe ataxic gait of the older mice was likely due to the dramatic loss of Purkinje cells, intensive astrogliosis and vacuolation of neurons in the deep cerebellar nuclei, and the severe vacuolation of the cells in vestibular and cochlear nuclei. The impaired bladder function and subsequent hydronephrosis were secondary to involvement of the central nervous system. These findings demonstrate that the glycosylasparaginase-deficient mice share many neuropathological features with human AGU patients, providing a suitable animal model to test therapeutic strategies in the treatment of the central nervous system effects in AGU.

A unique familial leukodystrophy with adult onset dementia and abnormal glycolipid storage: a new lysosomal disease?

Two adult siblings with early onset dementia are described. At presentation, in their early 30s, they showed poor judgment and disinhibition. A progressive dementia ensued over several years. Brain MRI disclosed diffusely increased T2 signal in the cerebral white matter, suggestive of a leukodystrophy. Numerous lysosomal enzyme assays including leucocyte arylsulphatase A and galactocerebrosidase activities, plasma and fibroblast very long chain fatty acid concentrations, and urinary sulphatide concentrations were normal, as were CSF analyses. A brain biopsy disclosed periodic acid Schiff (PAS) and Sudan black positive material in perivascular macrophages which, by electron microscopy, consisted of stacks of straight or curvilinear paired membranes within angulate lysosomes, indicative of abnormal glycolipid accumulation. The combination of clinical, radiological, biochemical, and pathological features of this degenerative disease is not consistent with that of any of the known leukodystrophies or lysosomal storage disorders. These findings suggest a previously undescribed familial glycolipid storage disorder causing an adult onset leukodystrophy and presenting with behavioural symptoms that mimic a psychiatric disorder.

Establishment and characterization of an Epstein-Barr virus-transformed B cell line, KM/C8, from a patient with infantile sialic acid storage disease

Nakano et al. have recently reported a Japanese case of infantile sialic acid storage disease [C. Nakano, Y. Hirabayashi, K. Ohno, T. Yano, T. Mito, M. Sakurai, Brain Dev., 18 (1996) 153-156]. For further etiological analysis of this disease, we prepared the Epstein-Barr virus (EBV)-transformed cell line (LCL) from the peripheral lymphocytes of this patient and performed initial characterization of the cells. Electron microscopy of the cells showed that the cells contained many vacuoles and swelled lysosomes. Cytochemical staining with sialic acid-specific lectin, Limax flavus agglutinin (LFA), showed strong staining on membranes and subcellular organelles on the patient-derived cells, whereas LCL from a normal person was only weakly stained. The cells from the patient contained 5.5-7.3 nmol/107 cells of free N-acetyl neuraminic acid, whereas three strains of LCLs derived from normal persons contained 1 nmol/107 cells. The culture supernatant of LCL from the patient contained 144 nmol/ml of free N-acetyl neuraminic acid, whereas the LCL culture supernatant from normal persons contained 57-73 nmol/ml of free sialic acid, which was the same or only at a slightly higher level than the fresh medium. In addition, cellular acidic sialidase measured as 4-methylumbelliferyl sialidase was elevated (107 nmol 4-methylumbelliferon released/mg cellular protein/60 min). The EBV-LCL from an ISSD patient is considered to remain as the abnormality of the cell donor.

Chronic arthritis in patients with aspartylglucosaminuria

OBJECTIVE

To study the frequency and clinical features of chronic inflammatory arthritis in aspartylglucosaminuria (AGU), a rare disorder of glycoprotein degradation inherited as an autosomal recessive trait and significantly more frequent in Finland than in other parts of the world.

METHODS

Of the 164 patients with AGU identified in Finland, 121 were examined by one of the authors, and 43 by their own physicians. For this study, we clinically reexamined all patients with AGU who had arthritis, and relevant laboratory and radiographic studies were performed.

RESULTS

Nine of 164 patients (5.5%) were found to have chronic inflammatory arthritis. In 5 patients, the symptoms had started in childhood. Five were seropositive for rheumatoid factor. Symmetric polyarthritis of both small and large joints was seen in 5 patients and erosions in 5. Seropositive rheumatoid arthritis was found in 3 first-degree relatives as well.

CONCLUSION

Chronic inflammatory arthritis is a feature of AGU and is characterized by onset in childhood, seropositivity for rheumatoid factor, and a deforming course.

Pathology of visceral organs and bone marrow in an acid sphingomyelinase deficient knock-out mouse line, mimicking human Niemann-Pick disease type A. A light and electron microscopic study

A recently generated aSmase knock-out mouse line develops a lethal storage disease which mimics the neurovisceral form of Niemann-Pick disease in man. In extension to the previously described neuropathological changes, the purpose of this study was to provide a detailed morphological, particularly ultrastructural analysis of the visceral organs of these animals including spleen, liver, intestine, lung, and kidney along with a sequential histological investigation of the bone marrow. Our results showed a progressive lysosomal storage as indicated by an increasing amount of foam cells in the bone marrow with age, extending to all visceral organs. Most severe storage phenomena were found in the mononuclear-macrophage system, however, parenchymal cells of visceral organs were also markedly involved. The ultrastructural appearance of membrane-bound inclusions displayed a pleomorphic aspect ranging from small vesicular and vesiculo-granular structures to huge lysosomes with membranous material deposited in lamellar or stacked arrays. The obvious similarity to its human counterpart along with an easy availability makes this animal model a valuable tool for further studies of Niemann-Pick disease type A.

A point mutation in the neu-1 locus causes the neuraminidase defect in the SM/J mouse

Lysosomal neuraminidase (sialidase) occurs in a high molecular weight complex with the glycosidase beta-galactosidase and the serine carboxypeptidase protective protein/cathepsin A (PPCA). Association of the enzyme with PPCA is crucial for its correct targeting and lysosomal activation. In man two genetically distinct storage disorders are associated with either a primary or a secondary deficiency of lysosomal neuraminidase: sialidosis and galactosialidosis. In the mouse the naturally occurring inbred strain SM/J presents with a number of phenotypic abnormalities that have been attributed to reduced neuraminidase activity. SM/J mice were originally characterized by their altered sialylation of several lysosomal glycoproteins. This defect was linked to a single gene, neu-1 , on chromosome 17, which was mapped by linkage analysis to the H-2 locus. In addition, these mice have an altered immune response that has also been coupled to a deficiency of the Neu-1 neuraminidase. Here we report the identification in SM/J mice of a single amino acid substitution (L209I) in the Neu-1 protein which is responsible for the partial deficiency of lysosomal neuraminidase. We propose that the reduced activity is caused by the enzyme's altered affinity for its substrate, rather than a change in substrate specificity or turnover rate. The mutant enzyme is correctly compartmentalized in lysosomes and maintains the ability to associate with its activating protein, PPCA. We propose that it is this mutation that is responsible for the SM/J phenotype.