Enzymic diagnosis of sphingolipidoses

Optimization of Enzyme Essays to Enhance Reliability of Activity Measurements in Leukocyte Lysates for the Diagnosis of Metachromatic Leukodystrophy and Gangliosidoses

(1) Lysosomal storage diseases are rare inherited disorders with no standardized or commercially available tests for biochemical diagnosis. We present factors influencing the quality of enzyme assays for metachromatic leukodystrophy (MLD) and gangliosidoses (GM1; GM2 variants B and 0) and validate the reliability and stability of testing in a retrospective analysis of 725 samples. (2) Patient leukocytes were isolated from ethylene-diamine-tetra-acetic acid (EDTA) blood and separated for subpopulation experiments using density gradient centrifugation or magnetic cell separation. Enzyme activities in whole leukocyte lysate and leukocyte subpopulations were determined. (3) The enzyme activities in leukocyte subpopulations differed significantly. Compared to lymphocytes, the respective enzyme activities were 2.31–4.57-fold higher in monocytes and 1.64–2.81-fold higher in granulocytes. During sample preparation, a considerable amount of the lysosomal enzymes was released from granulocytes. Nevertheless, with the sample preparation method used here, total leukocyte count proved to be more accurate than total protein amount as a reference unit for enzyme activities. Subsequent analysis of 725 individuals showed clear discrimination of enzyme activities in patient samples (48 MLD; 21 gangliosidoses), with a sensitivity of 100% and specificity of 98–99%.

Early detection of lysosomal diseases by screening of cases of idiopathic splenomegaly and/or thrombocytopenia with a next-generation sequencing gene panel

Lysosomal diseases (LD) are a group of about 70 rare hereditary disorders (combined incidence 1:5000) in which diverse lysosomal functions are impaired, impacting multiple organs and systems. The first clinical signs and symptoms are usually unspecific and shared by hundreds of other disorders. Diagnosis of LD traditionally relies on performing specific enzymatic assays, if available, upon clinical suspicion of the disorder. However, the combination of the insidious onset of LD and the lack of awareness on these rare diseases among medical personnel results in undesirable diagnostic delays, with unchecked disease progression, appearance of complications and a worsened prognosis. We tested the usefulness of a next‐generation sequencing‐based gene panel for quick, early detection of LD among cases of idiopathic splenomegaly and/or thrombocytopenia, two of the earliest clinical signs observed in most LD. Our 73‐gene panel interrogated 28 genes for LD, 1 biomarker and 44 genes underlying non‐LD differential diagnoses. Among 38 unrelated patients, we elucidated eight cases (21%), five with LD (GM1 gangliosidosis, Sanfilippo disease A and B, Niemann‐Pick disease B, Gaucher disease) and three with non‐LD conditions. Interestingly, we identified three LD patients harboring pathogenic mutations in two LD genes each, which may result in unusual disease presentations and impact treatment. Turnaround time for panel screening and genetic validation was 1 month. Our results underline the usefulness of resequencing gene panels for quick and cost‐effective screening of LDs and disorders sharing with them early clinical signs.

Lysosomal storage diseases

Lysosomal storage diseases (LSDs) are a group of over 70 diseases that are characterized by lysosomal dysfunction, most of which are inherited as autosomal recessive traits. These disorders are individually rare but collectively affect 1 in 5,000 live births. LSDs typically present in infancy and childhood, although adult-onset forms also occur. Most LSDs have a progressive neurodegenerative clinical course, although symptoms in other organ systems are frequent. LSD-associated genes encode different lysosomal proteins, including lysosomal enzymes and lysosomal membrane proteins. The lysosome is the key cellular hub for macromolecule catabolism, recycling and signalling, and defects that impair any of these functions cause the accumulation of undigested or partially digested macromolecules in lysosomes (that is, 'storage') or impair the transport of molecules, which can result in cellular damage. Consequently, the cellular pathogenesis of these diseases is complex and is currently incompletely understood. Several LSDs can be treated with approved, disease-specific therapies that are mostly based on enzyme replacement. However, small-molecule therapies, including substrate reduction and chaperone therapies, have also been developed and are approved for some LSDs, whereas gene therapy and genome editing are at advanced preclinical stages and, for a few disorders, have already progressed to the clinic.

Cerebral organoids derived from Sandhoff disease-induced pluripotent stem cells exhibit impaired neurodifferentiation

Sandhoff disease, one of the GM2 gangliosidoses, is a lysosomal storage disorder characterized by the absence of β-hexosaminidase A and B activity and the concomitant lysosomal accumulation of its substrate, GM2 ganglioside. It features catastrophic neurodegeneration and death in early childhood. How the lysosomal accumulation of ganglioside might affect the early development of the nervous system is not understood. Recently, cerebral organoids derived from induced pluripotent stem (iPS) cells have illuminated early developmental events altered by disease processes. To develop an early neurodevelopmental model of Sandhoff disease, we first generated iPS cells from the fibroblasts of an infantile Sandhoff disease patient, then corrected one of the mutant HEXB alleles in those iPS cells using CRISPR/Cas9 genome-editing technology, thereby creating isogenic controls. Next, we used the parental Sandhoff disease iPS cells and isogenic HEXB-corrected iPS cell clones to generate cerebral organoids that modeled the first trimester of neurodevelopment. The Sandhoff disease organoids, but not the HEXB-corrected organoids, accumulated GM2 ganglioside and exhibited increased size and cellular proliferation compared with the HEXB-corrected organoids. Whole-transcriptome analysis demonstrated that development was impaired in the Sandhoff disease organoids, suggesting that alterations in neuronal differentiation may occur during early development in the GM2 gangliosidoses.

Laboratory Diagnosis of Canine GM2-Gangliosidosis using Blood and Cerebrospinal Fluid

In the present study, laboratory techniques were used to diagnose canine GM2-gangliosidosis using blood and cerebrospinal fluid (CSF) that can be collected noninvasively from living individuals. Lysosomal acid β-hexosaminidase (Hex) was measured spectrofluorometrically using 4-methylumbelliferyl N-acetyl-β-d-glucosaminide and 4-methylumbelliferyl 7-(6-sulfo-2-acetamido-2-deoxy-β-d-glucopyranoside) as substrates. Main isoenzymes A and B of Hex in leukocytes were also analyzed using cellulose acetate membrane electrophoresis. GM2-ganglioside in CSF was detected and determined quantitatively by using thin-layer chromatography/enzyme-immunostaining method with anti-GM2-ganglioside antibody. In normal dogs, Hex activities could be determined in leukocytes, serum, and CSF, and the total activities were markedly reduced in all the enzyme sources in a dog with Sandhoff disease. Electrophoresis of a leukocyte lysate from a normal dog showed that the Hex A and Hex B were not separated distinctively with formation of a broad band, whereas there were no bands in electrophoresis of a lysate from a dog with Sandhoff disease, showing a deficiency in the total enzyme activity. GM2-ganglioside could be detected and determined quantitatively in as little as 100 μl of canine CSF. GM2-ganglioside in CSF in a dog with Sandhoff disease increased to 46 times the normal level. In conclusion, the methods in the present study are useful for diagnosis of canine GM2-gangliosidosis. These techniques enable definitive and early diagnosis of canine GM2-gangliosidosis even if tissues and organs cannot be obtained.

Morphological analysis of corneal opacity in Shiba dog with GM1 gangliosidosis

GM1 gangliosidosis is one of the inherited metabolic lysosomal storage disorders characterized by neurological symptoms caused by beta-galactosidase deficiency and consequent accumulation of GM1 ganglioside in neuronal cells. Shiba dogs affected with GM1 gangliosidosis have been found to suffer from corneal opacity. In our morphological analysis, keratocyte enlargement was induced by abnormal intracellular accumulation of neutral carbohydrates, resulting in the loss of normal arrangement of collagen fibrils in the opaque cornea was found to be associated with the disorder. We therefore conclude that corneal opacity in this Shiba dog with GM1 gangliosidosis may be caused by neutral carbohydrate accumulation in lysosomes, swelling and dysfunction of keratocytes, and subsequent irregular arrangement of collagen fibrils in the corneal proper substance.

Retrospective diagnosis of feline GM2 gangliosidosis variant 0 (Sandhoff-like disease) in Japan: possible spread of the mutant allele in the Japanese domestic cat population

GM2 gangliosidosis variant 0 (human Sandhoff disease) is a lysosomal storage disease caused by simultaneous deficiencies of acid beta-hexosaminidase (Hex) A and Hex B due to an abnormality of beta-subunit, a common component in these enzyme molecules, which is coded by the HEXB gene. In the present study, a retrospective diagnosis was performed in 2 previous suspected cases of feline Sandhoff-like disease using a DNA test to detect the causative mutation identified previously in 4 cats in 2 other families of Japanese domestic cats. Enzymic analysis was also performed using stored leukocytes and plasma collected from the subject families in order to investigate the usefulness of enzymic diagnosis and genotyping of carriers. The DNA test suggested that the 2 cases were homozygous recessive for the mutation. Consequently, 6 cats homozygous for the same mutation have been found in 4 separate locations of Japan, suggesting that this mutant allele may be spread widely in the Japanese domestic cat populations. In enzymic analysis, Hex A and Hex B activities in leukocytes and plasma measured using 4-methylumbelliferyl N-acetyl-beta-D-glucosaminide as a substrate were negligible in affected cats, compared with those in normal and carrier cats. However, there was a wide overlap in enzyme activity between normal and carrier cats. Therefore, it was concluded that enzymic analysis is useful for diagnosis of affected cats, but is not acceptable for genotyping of carriers.

Isofagomine increases lysosomal delivery of exogenous glucocerebrosidase

Intravenous enzyme replacement therapy (ERT) with purified glucocerebrosidase (GLA) leads to significant improvement of the clinical manifestations in patients with Type 1 Gaucher disease. However, the high doses required, slow response and inability to recover most of the infused enzyme in the target tissues may be attributed to losses occurring during transit en route to the lysosome. Preincubation of GLA with isofagomine (IFG), a slow-binding inhibitor, significantly increased stability of the enzyme to heat, neutral pH and denaturing agents in vitro. Preincubation of GLA with isofagomine prior to uptake by cultured cells results in increased intracellular enzyme activity accompanied by an increase in enzyme protein suggesting that reduced denaturation of GLA in the presence of isofagomine leads to a decrease in the degradation of the enzyme after internalization. Preincubation of GLA with slow-binding inhibitors before infusion may improve the effectiveness of ERT for Gaucher disease.

Clinical and molecular analysis of GM2 gangliosidosis in two apparent littermate kittens of the Japanese domestic cat

This case report documents clinical and molecular findings in two littermate kittens of the Japanese domestic cat with GM2 gangliosidosis variant 0. Analysis included detailed physical, magnetic resonance imaging, biochemical, pathological and genetic examinations. At first, these littermate kittens showed typical cerebellar signs at approximately 2 months of age. About 2 months later, they progressively showed other neurological signs and subsequently died at about 7 months of age. Magnetic resonance imaging just before the death showed an enlarged ventricular system, T1 hyperintensity in the internal capsule, and T2 hyperintensity in the white matter of the whole brain. Histological findings suggested a type of lysosomal storage disease. Biochemical studies demonstrated that the kittens were affected with GM2 gangliosidosis variant 0, and a DNA assay finally demonstrated that these animals were homozygous for the mutation, which the authors had identified in a different family of the Japanese domestic cat. The findings in the present cases provide useful information about GM2 gangliosidosis variant 0 in Japanese domestic cats.

Labeling strategies for bioassays

Different labeling strategies for enzymatic assays and immunoassays are reviewed. Techniques which make use of direct detection of a label, e.g. radioimmunoassays, are discussed, as are techniques in which the label is associated with inherent signal amplification. Examples of the latter, e.g. enzyme-linked immunosorbent assays or nanoparticle-label based assays, are presented. Coupling of the bioassays to chromatographic separations adds selectivity but renders the assays more difficult to apply. The advantages and drawbacks of the different analytical principles, including future perspectives, are discussed and compared. Selected applications from clinical, pharmaceutical, and environmental analysis are provided as examples.

Comparison of polymerase chain reaction-restriction fragment length polymorphism assay and enzyme assay for diagnosis of G(M1)-gangliosidosis in Shiba dogs

In the present study, diagnostic methods for canine G(M1)-gangliosidosis were examined by comparing a DNA mutation assay with an enzyme assay. Sixty-two Shiba dogs of a pedigree with G(M1)-gangliosidosis were differentiated into 3 genotypes, i.e., normal, heterozygous, and homozygous affected dogs, using a DNA mutation assay, which consists of polymerase chain reaction amplification and the determination of restriction fragment length polymorphisms. The beta-galactosidase activity in leukocytes, umbilical cords, and plasma was measured using 4-methylumbelliferyl beta-D-galactoside and p-nitrophenyl beta-D-galactoside as artificial substrates and compared among the 3 genotypes. The results showed that it was possible to identify homozygous dogs with the enzyme assay using leukocytes and umbilical cords. When using leukocytes, heterozygous carriers could be differentiated from normal dogs in many cases. However, the use of the DNA mutation assay is essential for a complete determination of heterozygous carriers because of the overlap in the distribution of enzyme activity between these 2 groups. When umbilical cords were used, heterozygous carriers could not be differentiated from normal dogs because of no significant difference in enzyme activity between these 2 groups. The beta-galactosidase activity in plasma was not applicable to the diagnosis and genotyping of G(M1)-gangliosidosis in Shiba dogs.

Toxicity of glucosylsphingosine (glucopsychosine) to cultured neuronal cells: a model system for assessing neuronal damage in Gaucher disease type 2 and 3

Patients with Gaucher disease have been classified as type 1 nonneuronopathic, type 2 acute neuronopathic, and type 3 chronic neuronopathic phenotypes. Increased quantities of glucocerebroside and glucosylsphingosine (glucopsychosine) are present in the brain of type 2 and type 3 Gaucher patients. Galactosylsphingosine has previously been shown to be neurotoxic in globoid cell leukodystrophy (Krabbe disease). To determine whether glucosylsphingosine is also neurotoxic, we examined its effect on cultured cholinergic neuron-like LA-N-2 cells. When these cells were exposed to 1, 5, or 10 microM glucosylsphingosine for a period of 18 h, they became shriveled, neurite outgrowth was suppressed, and the activities of the lysosomal enzymes glucocerebrosidase, sphingomyelinase, and beta-galactosidase were reduced in a dose-dependent manner. Acetylcholine in cells exposed to glucosylsphingosine also declined. Cells switched to glucosylsphingosine-free medium partially recovered. The data suggest that accumulation of glucosylsphingosine contributes to neuronal dysfunction and destruction in patients with neuronopathic Gaucher disease.

Correlation between enzyme activity and substrate storage in a cell culture model system for Gaucher disease

Gaucher disease, the most common sphingolipidosis, is caused by a decreased activity of glucosylceramide beta-glucosidase, resulting in the accumulation of glucosylceramide in macrophage-derived cells known as Gaucher cells. Much of the storage material is thought to originate from the turnover of cell membranes, such as phagocytosed red and white blood cells. In this study, an in vitro model of Gaucher disease was developed by treating the murine macrophage cell line J774 with a specific inhibitor of glucosylceramide beta-glucosidase, conduritol B-epoxide, and feeding red blood cell ghosts, in order to mimic the disease state. It was found in this model system that glucosylceramide beta-glucosidase activity could be reduced to about 11-15% of the normal control level before increased storage of glucosylceramide occurred. This in vitro system allows insight into the correlation between enzyme activity and lipid storage as predicted by the theory of residual enzyme activity that was proposed by Conzelmann and Sandhoff.

Caveolin expression and localization in human keratinocytes suggest a role in lamellar granule biogenesis

Lamellar granules are sphingolipid-enriched organelles, probably intimately related to the tubulo-vesicular elements of the trans-Golgi network, that deliver the precursors of stratum corneum barrier lipids to the extracellular compartment. Caveolins are cholesterol-binding scaffolding proteins that facilitate the assembly of cholesterol- and sphingolipid-enriched membrane domains known as caveolae. Similarities in the composition of lamellar granules and caveolae suggest that caveolins could be involved in lamellar granule assembly, trafficking, and/or function. In order to explore this relationship, we have examined the expression of caveolins in epidermis, keratinocyte cultures, and an isolated lamellar granule fraction using immunolabeling, immunoblotting, and northern blotting. Several antibodies show immunolocalization of caveolin-1 in the basal layer of human epidermis, with a decline in the suprabasal layers and a reemergence of expression at the stratum granulosum/stratum corneum junction. Two of three caveolin-2 antibodies show little basal staining, but strong signal throughout the rest of the epidermis, whereas a third shows a pattern like caveolin-1. An antibody against caveolin-3 shows a strong signal at the stratum granulosum/stratum corneum interface. Caveolins partially colocalize with glucocerebrosidase, an enzyme known to be critical for remodeling of extruded lamellar granule contents, with AE17, a previously described lamellar-granule-associated antibody, and with glucosylceramides, a major lipid component of lamellar granules. Caveolin-1 protein is present in undifferentiated low-calcium-grown keratinocyte cultures, decreases upon induction of differentiation, and then rises to levels above those seen in undifferentiated cultures, consistent with the immunofluorescence findings. Caveolin-1 mRNA expression parallels that of the protein. Caveolin-2 mRNA and protein expression were unchanged over the course of culture differentiation. Keratinocyte caveolin-1 mRNA expression is not induced by an increase in medium calcium level and is markedly reduced by phorbol-ester-mediated protein kinase C induction. Caveolin-1 is enriched in an isolated lamellar granule fraction that is also enriched, as we have previously described, in lysosomal acid lipase and glucocerebrosidase, and localizes to structures consistent with lamellar granules on immunoelectron microscopy. The differentiation-dependent expression of caveolin-1, the colocalization of caveolins with putative lamellar-granule-associated antigens, their enrichment in isolated lamellar granules, and their presence in lamellar-granule-like structures on immunoelectron microscopy, along with their known structural role in the assembly of glycosphingolipid- and cholesterol-enriched domains in other cell types, suggest that caveolins may play a role in lamellar granule assembly, trafficking, and/or function.

Clinical and clinico-pathologic characteristics of Shiba dogs with a deficiency of lysosomal acid beta-galactosidase: a canine model of human GM1 gangliosidosis

The present study was conducted to determine the clinical and clinico-pathologic characteristics of Shiba dogs with GM1 gangliosidosis, which is due to an autosomal recessively inherited deficiency of lysosomal acid beta-galactosidase activity. Clinical and clinico-pathological features were investigated in 10 homozygous Shiba dogs with GM1 gangliosidosis. The age at onset was 5 to 6 months and the dogs manifested progressive neurologic signs including loss of balance, intermittent lameness, ataxia, dysmetria and intention tremor of the head. The dogs were unable to stand by 10 months of age due to a progression of ataxia and spasticity in all limbs. Corneal clouding, a visual defect, generalized muscle rigospasticity, emotional disorder and a tendency to be lethargic were observed at 9 to 12 months. The dogs became lethargic from 13 months of age. The survival period seemed to be 14 to 15 months. As a clinico-pathologic feature, lymphocytes with abnormally large vacuoles were observed in peripheral blood (30 to 50% of total lymphocytes) through the lifetime of the dogs. The clinical and clinico-pathologic characteristics of this animal model are useful for not only the development and testing of potential methods of therapy, but also the diagnosis of affected homozygous Shiba dogs in veterinary clinics.

Uptake of mannose-terminal glucocerebrosidase in cultured human cholinergic and dopaminergic neuron cell lines

Enzyme replacement therapy has been shown to be particularly effective for patients with type 1 (non-neuronopathic) Gaucher disease. However, intravenously administered glucocerebrosidase does not reverse or halt the progression of brain damage in patients with type 2 (acute neuronopathic) Gaucher disease. A previous investigation revealed that intracerebral infusion of mannose-terminal glucocerebrosidase was safe in experimental animals. The enzyme had a comparatively long half-life in the brain. It was transported by convection from the site of infusion along white matter fiber tracts to the cerebral cortex where it was endocytosed by neurons. In anticipation of intracerebral administration of mannose-terminal glucocerebrosidase to patients with type 2 Gaucher disease, it was important to learn the mechanism involved in its cellular uptake. We therefore compared the endocytosis of this enzyme by J774 macrophage cells with that in two human neuronal cell lines and a human astrocyte cell line. Mannose-terminal glucocerebrosidase was taken up by cholinergic LA-N-2 cells, but to a much lower extent than by macrophages. Considerably less of the enzyme was endocytosed by dopaminergic SH-SY5Y cells. It was not taken up by NHA astrocytes. The findings provide encouragement for an exploration of intracerebral administration of glucocerebrosidase in patients with type 2 Gaucher disease.

GM1 gangliosidosis in shiba dogs

A six-month-old shiba dog with a one-month history of progressive motor dysfunction showed clinical signs of a cerebellar disorder, including ataxia, dysmetria and intention tremor of the head. Histopathological and ultrastructural studies revealed distended neurons packed with membranous cytoplasmic bodies throughout the central nervous system. The activities of lysosomal acid beta-galactosidase in its leucocytes and liver were less than 2 per cent of the control levels, and the compound accumulated in the brain was identified as GM1 ganglioside. A sibling which died immediately after birth was shown to have a beta-galactosidase deficiency in the brain and visceral organs. A family study revealed that the sire and dam of the probands were heterozygotes with approximately half of the normal level of beta-galactosidase activity, suggesting an autosomal recessive pattern of inheritance.

Characterization of the GALC gene in three Japanese patients with adult-onset Krabbe disease

Krabbe disease, a neurodegenerative disorder of autosomal recessive inheritance, is caused by mutations in the galactosylceramidase (GALC) gene. However, its clinical manifestations in terms of time of onset and severity are heterogeneous. Thus, elucidation of the relationship of symptoms to the site and type of mutation is important, both for an understanding of the etiology of the disease and for diagnostic purposes. We examined the genomic structure of the GALC gene in three unrelated adult-onset Krabbe disease patients. One patient was homozygous for an Ile66Met mutation. Another patient who appeared to express only one mutated mRNA species was, in fact, a compound heterozygote for an Ile66Met mutation and a nonsense mutation, Tyr354ter. Because the allele with the nonsense mutation was not detectable by mRNA analysis, a rapid degradation of the mRNA caused by premature chain termination was suggested. The third patient who carried two inactiving mutations--Leu618Ser and a second resulting in exon 6 skipping--was also found to carry an intronic mutation, IVS6 + 5G > A. Transfection experiments using a GALC mini-gene proved that this intronic mutation was the cause for the exon 6 skipping.

Expression and processing of recombinant human galactosylceramidase

Stable transformants of CHO cells that overexpress human galactosylceramidase (GALC) were established. The GALC within the cell consisted of 50- and 30-kDa proteins. The active GALC secreted into the culture medium in large amounts consisted of the 80-kDa precursor enzyme. We confirmed that the precursor enzyme was taken up by fibroblasts via the mannose-6-phosphate receptor and processed into the 50- and 30-kDa fragments. Fragmentation was inhibited by the lysosomotropic agents chloroquine and NH4Cl, suggesting that it occurs within the lysosome. GALC mutations identified in globoid cell leukodystrophy suppressed fragmentation. Neither the 50- or 30-kDa fragment expressed had GALC activity, indicative that the entire structure is necessary for enzyme activity and that fragments expressed separately cannot associate to form the active enzyme.

Early infantile Krabbe disease: deceptively normal magnetic resonance imaging and serial neurophysiological studies

Early infantile Krabbe disease is a progressive neurodegenerative disease caused by deficiency of lysosomal enzyme galactocerebroside beta-galactosidase, with onset before the age of 6 months. We present serial clinical, radiological and neurophysiological findings of a patient with early infantile Krabbe disease, presenting at the third day of life with hypotonia, macrocephaly and neonatal seizures. The patient had a deceptively normal initial magnetic resonance imaging examination at the age of 3 months, with progression of the white matter disease over the following 9 months, showing a clinical picture of profound hypotonia with pyramidal and pseudobulbar signs, as well as mild optic atrophy. Assay of galactocerebroside beta-galactosidase activity in leukocyte culture disclosed a marked deficiency of the enzyme (0.00 nmol/mg protein per h with normal values > 0.7 nmol/mg protein per h), thus confirming the diagnosis of Krabbe disease. Nerve conduction velocity and evoked potential studies, as well as the electroencephalogram, were abnormal at the age of 6 months, while serial neurophysiological studies at the age of 12 and 18 months demonstrated the progressive nature of the disease.

Increased globotriaosylceramide in familial dysautonomia

Familial Dysautonomia (FD) is an autosomal recessive disease of unknown etiology, occurring primarily in Ashkenazi Jews. Patients are neurologically impaired, with deficits primarily in autonomic and sensory functions. The biochemical and genetic defects have remained elusive, precluding carrier detection and prenatal diagnosis. High-performance liquid chromatography data indicated up to a threefold increase in the neutral glycosphingolipid globotriaosylceramide in Dysautonomic fibroblasts and lymphoblasts. Total ganglioside values, measured by colorimetric, fluorometric or specific sodium borohydride incorporation, were decreased. Affected fibroblasts exhibited a range of pleomorphic phenotypes, such that the usual swirl-like confluent growth pattern of normal fibroblasts was distorted to varying degrees, suggesting abnormalities in the FD plasma membrane, possibly affecting cell-cell contacts. The glycosphingolipid increase could not be accounted for on the basis of markedly decreased alpha-galactosidase activity, as in Fabry's disease, where patients also display decreased autonomic function.

Effect of experimental conditions on the appearance of distinct forms of placental glucosylceramidase: use of gel filtration analysis as a means of ascertaining their occurrence

We have found that, under some experimental conditions, the placental glucosylceramidase shows an anomalous behaviour on gel filtration chromatography. At pH 5.6, the optimal pH of the enzymatic assay, the purified enzyme remains bound to either Superose 6 or TSK-40-XL HPLC columns, while the interaction of the crude glucosylceramidase contained in the water extract of the lysosome-mitochondrial fraction of placenta with the two HPLC gel matrices is much weaker. The quite different behaviour of the crude compared to the purified enzyme may be explained by the formation in the crude preparation of associated form(s) of glucosylceramidase with suitable endogenous compound(s), which compete with the gel matrices for the binding to the enzyme. The most likely one component of the enzyme complex is the placental activating factor, previously reported by us (Vaccaro et al. (1985) Biochim. Biophys. Acta 836, 157-166), as indicated by the negligible stimulation of the crude enzyme activity on addition of the factor, either before or after passage through the HPLC columns. On the assumption that the behaviour of crude glucosylceramidase on gel filtration becomes similar to that of the purified enzyme when its interaction with endogenous substance(s) is impaired, we have identified some conditions which prevent the formation of the enzyme associated form(s): (a) the addition of guanidine chloride (0.2 M), a cahotropic agent, to the crude preparation; and (b) the increase of pH up to 8. In conclusion, taking advantage of the anomalous behaviour of glucosylceramidase on gel filtration chromatography, evidence has been obtained that placental glucosylceramidase may occur under several forms which had not been previously reported; a difference in experimental conditions can promote the formation of one or another form, by possibly affecting the composition and/or the stoichiometry and/or the stability of the enzyme complex.

Juvenile Sandhoff disease: a Japanese patient carrying a mutation identical to that found earlier in a Canadian patient

A 35-year-old Japanese man with juvenile Sandhoff disease is described. He showed progressive neurogenic muscular atrophy, cerebellar ataxia and mental deterioration, beginning at age 10 years. The accumulation of GM2 ganglioside in the submucosal nerve cell was confirmed by positive immunostaining using anti-GM2 ganglioside antibody. Biochemical evaluation revealed nearly absent beta-hexosaminidase A and B activities in leukocytes and cultured fibroblasts. Hydrolysis of [3H]globoside I in the intact fibroblasts was apparently disturbed but the rate of hydrolysis was higher than those seen in cells from patients with infantile Sandhoff disease. Analysis of the beta-hexosaminidase beta-subunit gene of the patient disclosed a point mutation (a G-to-A transition) within intron 12. The mutation generates a new splice junction resulting in a 24-base insertion between exons 12 and 13 in the processed mRNA and consequently an 8-amino acid insertion in the translation product. This mutation is identical to that originally found in a Canadian patient with juvenile Sandhoff disease. A possible relationship with the clinical phenotype and the gene abnormality is discussed.

Intercellular transport of lysosomal acid lipase mediates lipoprotein cholesteryl ester metabolism in a human vascular endothelial cell-fibroblast coculture system

We present results from studies of human cell culture models to support the premise that the extracellular transport of lysosomal acid lipase has a function in lipoprotein cholesteryl ester metabolism in vascular tissue. Vascular endothelial cells secreted a higher fraction of cellular acid lipase than did smooth muscle cells and fibroblasts. Acid lipase and lysosomal beta-hexosaminidase were secreted at approximately the same rate from the apical and basolateral surface of an endothelial cell monolayer. Stimulation of secretion with NH4Cl did not affect the polarity. We tested for the ability of secreted endothelial lipase to interact with connective tissue cells and influence lipoprotein cholesterol metabolism in a coculture system in which endothelial cells on a micropore filter were suspended above a monolayer of acid lipase-deficient (Wolman disease) fibroblasts. After 5-7 d, acid lipase activity in the fibroblasts reached 10%-20% of the level in normal cells; cholesteryl esters that had accumulated from growth in serum were cleared. Addition of mannose 6-phosphate to the coculture medium blocked acid lipase uptake and cholesterol clearance, indicating that lipase released from endothelial cells was packaged into fibroblast lysosomes by a phosphomannosyl receptor-mediated pathway. Supplementation of the coculture medium with serum was not required for lipase uptake and cholesteryl ester hydrolysis by the fibroblasts, but was necessary for cholesterol clearance. Results from our coculture model suggest that acid lipase may be transported from intact endothelium to cells in the lumen or the wall of a blood vessel. We postulate that delivery of acid hydrolases and lipoproteins to a common endocytic compartment may occur and have an impact on cellular lipoprotein processing.

Correlation between the activity of glucosylceramidase and its binding to glucosylceramide-containing liposomes. Role of acidic phospholipids and fatty acids

Optimal enzymatic hydrolysis of glucosylceramide inserted into liposomes has been obtained when both acidic phospholipids and the appropriate fatty acids were added to glucosylceramide-containing liposomes. In fact, the stimulation of glucosylceramidase by acidic phospholipids was synergistically enhanced by fatty acids, whose effect was dependent upon chain length and increased on unsaturation. By following the partition of glucosylceramidase between the aqueous phase and the liposome-associated state with a flotation procedure, it has been found that phosphatidic acid (PA) and oleic acid (OA), as representatives of acidic phospholipids and activating fatty acids, respectively, were both required not only for optimal glucosylceramidase activity, but also for a tight binding of the enzyme to the liposomes. The binding was significantly less effective in the absence of either PA or OA. In the absence of both PA and OA no physical interaction between the enzyme and the liposomes was observed. Under all conditions, the glucosylceramidase activity directly correlated with the enzyme binding to the substrate-containing liposomes. Additionally, we have obtained evidence that the site(s) of the enzyme involved in the binding to the liposomes is distinct from the catalytic site; in fact, the enzyme could still associate with liposomes containing PA and OA but devoid of glucosylceramide, while it was incapable of binding to glucosylceramide-containing liposomes in the absence of PA and OA. In conclusion, the presence in liposomes of acidic phospholipids together with the appropriate fatty acids plays a key role in promoting the binding of glucosylceramidase. Consequently, when glucosylceramide is also included in the liposomes, its hydrolysis is markedly enhanced by these acidic lipids.

Prevalence of different types of lysosomal storage diseases in Saudi Arabia

The frequency of different types of lysosomal storage diseases in 125 referred cases, collected over three years, was compared to the occurrence elsewhere. The data suggest that mucopolysaccharidosis (MPS) type IVA (Morquio disease), multiple sulphatase deficiency, Niemann-Pick disease type B, GM2 gangliosidosis type '0' (Sandhoff disease), and ceroid lipofuscinosis (Jansky-Bielschowsky and Batten-Spielmeyer-Vogt syndromes) are encountered frequently in Saudi Arabia, as compared to other storage diseases. In contrast, some other diseases such as the adult variant of Gaucher's disease were not observed. Half of the GM2 gangliosidosis type '0' cases originated from one large tribe in the country. Other conditions did not show tribal predilection. The ceroid lipofuscinosis cases in Saudi Arabia originated from four large families. Consanguineous marriages taking place within tribal boundaries probably account for the pattern observed.

Beta-glucosidase activity in liver, spleen and brain in acute neuropathic Gaucher disease

We examined the property of beta-D-glucosidase in normal child liver, spleen and brain tissues and in tissues affected by Gaucher disease using two different kinds of synthetic substrates, 2-hexadecanoylamino-4-nitrophenyl-beta-D-glucopyranoside (HN Glc) and 4-methylumbelliferyl-beta-D-glucopyranoside (MU Glc). HN glucosidase activity was noted only in the particulate fraction of each organ tissues of the normal child, and it was deficient in the tissue affected by Gaucher disease. MU glucosidase activity in the whole homogenate and the soluble fraction showed normal levels for the liver and brain tissue of the Gaucher patient. However, MU glucosidase activity in the particulate fraction, at the vicinity of pH 4.5, for the liver, spleen and brain tissue was deficient in the affected patient. HN Glc was a very easy and useful substrate for the diagnosis of Gaucher disease, but it was not very sensitive. While MU Glc was very sensitive, it was necessary to remove the non-specific beta-D-glucosidase for the diagnosis of Gaucher disease.

A case of Fabry's disease in a patient with no alpha-galactosidase A activity caused by a single amino acid substitution of Pro-40 by Ser

We analyzed a male patient with Fabry's disease who had no activity of the lysosomal hydrolase alpha-galactosidase A (alpha-GalA) and female members of his family. We cloned a cDNA that encoded the mutant alpha-GalA, determined its nucleotide sequence, and found two nucleotide differences between the mutant and the wild-type cDNAs. Although one difference was silent, the other difference, a C-to-T transition at nucleotide number 118, resulted in an amino acid substitution of Pro-40 by Ser. A transient expression assay demonstrated that this missense mutation was the cause of the deficiency of alpha-GalA activity in the patient. In vitro mutagenesis experiments demonstrated that Pro-40 is critical for the appearance of alpha-GalA activity.

Metabolism of free sphingoid bases in murine tissues and in cultured human fibroblasts

Metabolism of free sphingoid bases present in normal tissues [Kobayashi, T., Mitsuo, K. & Goto, I. (1988) Eur. J. Biochem. 172, 747-752] was examined in mouse tissues and in human cultured fibroblasts. Subcellular fractionation studies of the mouse liver revealed most of free sphingoid bases to be in the membrane fractions. Fibroblasts from patients with Farber's disease contained concentrations of free sphingoid bases similar to those seen in the normal fibroblasts. When L-cycloserine, a potent inhibitor of the first reaction of sphingoid base synthesis, was added to the culture medium, the concentration of free sphingoid bases in fibroblasts decreased, dose-dependently. Thus, most of the free sphingoid bases in the tissue probably do not derive from the degradation of sphingolipids but are newly synthesized. Free sphingoid bases in microsomes from the brainstem and spinal cord were acylated or glycosylated when incubated with acyl-CoA or UDP-glycoside. However, the reaction for the synthesis of ceramide was much greater and more rapid than that of glycosylsphingosine synthesis. In liver microsomes, ceramide synthesis from endogenous free sphingoid bases was observed but synthesis of glycosylsphingosine was not evident. Therefore, the main pathway of metabolism of free sphingoid bases is presumably acylation (to ceramide) but not glycosylation (to lysoglycosphingolipid).

Multiple sulfatase deficiency with a novel biochemical presentation

Deficient activities of cerebroside-sulfatase, N-Acetylgalactosamine-4-sulfatase and iduronide 2-sulfatase in the lymphocytes of a patient suspected of metachromatic leukodystrophy, established the diagnosis of multiple sulfatase deficiency (MSD). Cultured skin fibroblasts (of early passage) from the patient had normal levels of activity for the three sulfatases. One week after the first examination, the activities of the three sulfatases in the fibroblasts of the patient declined and within a month were 4%-29% of normal. Total urinary glycosaminoglycans were within normal range. However, further examination showed an increase in the concentration of heparan sulfate, which comprised more than 50% of the total, compared with less than 20% in normal controls. Urinary sulfatides, cholesterol esters, cholesterol, and triglycerides were increased. The results from the study of this unique case of MSD suggest that time-dependent changes affect the activities of sulfatases in MSD. These results also demonstrate the necessity of assaying the sulfatases in both lymphocytes and fibroblasts from suspected cases of MSD.

Neurological and neurobehavioral development of the mutant 'twitcher' mouse

The present study described the neurological and locomotor development of the mutant 'twitcher' mouse (B57BL/6J-twi), an enzymatically authentic model of globoid cell (Krabbe) leukodystrophy. Comparisons were made on a neurological developmental battery and a series of behavioral tests, including open field, rotorod, and hangtime performance. Homozygous affected (twi/twi), heterozygous carriers (+/twi) and homozygous normals (+/+) were compared. Neurological development was slowed in twi/twi with some subtler differences between +/twi and normals. Twi/twi reached all functional milestones except grasp. There was a rapid deterioration of motor indices after 20 days of age. However, most sensory markers were preserved. On hangtime, there were significant differences from normal for both twi/twi and +/twi at 15 days of age and across the 15-30 day developmental stage, with the +/twi males slightly more impaired. On the rotorod, all animals were equally unable to stay on the rod at 15 days of age and neither male nor female twi/twi showed significant development. Male +/twi lagged significantly behind male +/+. In the open field, all groups were equally inactive at 13-15 days and showed similar increases in activity, rearing, and grooming until weaning. All groups peaked immediately after weaning and declined thereafter, with twi/twi showing the lowest activity. The data were discussed in terms of the relationship between the human disease and the animal model.

Hematopoietic cell transplantation in murine globoid cell leukodystrophy (the twitcher mouse): effects on levels of galactosylceramidase, psychosine, and galactocerebrosides

Hematopoietic cell transplantation (HCT) prolongs survival in the twitcher mouse, an authentic animal model of human globoid cell leukodystrophy (Krabbe disease; galactosylceramidase deficiency), but the effects of HCT on levels of galactosylceramidase, psychosine, and cerebrosides in the tissues of twitcher mice have not been previously studied. Galactosylceramidase was less than 8% of control activity in tissues of untreated twitcher mice but reached normal values in brain and spleen and 20-30% of control in kidney of 100-day-old twitchers that received HCT at age 10 days. Using a recently developed method for the simultaneous determination of psychosine and cerebrosides, we measured the tissue levels of these lipids in the above animals. The levels of psychosine in brain, sciatic nerve, and kidney of untreated twitcher mice were 44, 200, and 12 times control values, respectively, in 30-day-old animals and 69, 500, and 14 times control levels in 40-day-old mice. On the other hand, levels of cerebroside were approximately 35% of control values in sciatic nerve, remained about the same in the brain, and were elevated 10-fold in the kidney of twitcher mice. After HCT, psychosine levels in the brains of 30-day-old twitchers were lowered to 30-35% of values in untreated twitchers, and the levels remained in that range during the post-HCT period. Similarly, brain cerebroside levels remained low in HCT-treated twitcher mice. Although psychosine levels in sciatic nerves of HCT-treated twitcher mice increased more slowly than in the nerves of untreated twitchers, the levels in 100-day-old HCT-treated twitcher mice had reached the same high values as those seen in untreated 40-day-old twitchers. It is not known whether the extremely high levels of psychosine in sciatic nerves ultimately contribute to the death of twitcher mice after HCT.

A case of heterozygous Fabry's disease with a short PR interval and giant negative T waves

A 55 year old woman with heterozygous Fabry's disease presented with cardiac symptoms. The electrocardiogram showed a PR interval of 0.12 s and giant negative T waves, suggesting apical hypertrophic cardiomyopathy. Endomyocardial biopsy, however, revealed myelin like substances characteristic of Fabry's disease. Increasing thickness of the left ventricular wall was seen by echocardiography over a period of five years. A deficiency of alpha galactosidase activity in the leucocytes confirmed the diagnosis of Fabry's disease, although this patient had neither angiokeratoma or proteinuria. The possibility of Fabry's disease should be considered in patients with cardiomegaly of unknown cause and the following electrocardiographic abnormalities: a PR interval less than or equal to 0.12 s, high voltage QRS complexes in the left precordial leads, and giant negative T waves.

Complementation studies with clinical and biochemical characterizations of a new variant of multiple sulphatase deficiency

A patient with a new variant of multiple sulphatase deficiency (MSDv) is reported. Unlike the usual type, onset was late and progress was slow. The phenotypic changes were those usually seen in multiple sulphatase deficiency but much milder. Cytoplasmic accumulations were found in skin fibroblasts, and urinary mucopolysaccharides and sulphatides were high. Arylsulphatases A, B and C (ASA, B and C), heparan N-sulphatase sulphoiduronate sulphatase, and N-acetylgalactosamine 6-sulphatase all had low activity in lymphocytes and cultured skin fibroblasts. Complementation for ASA activity was found in hybrids between MSDv and metachromatic leukodystrophy (MLD) as well as between multiple sulphatase deficiency (MSD) and MLD. Complementation for ASC activity was also seen in hybrids between MSDv and X-linked ichthyosis (XLI), and between MSD and XLI. However, neither ASA nor ASC activity increased in hybrid cells of MSDv and MSD. These results suggested that the mutations of MSDv and of MSD were allelic, although of different phenotypes.

Late-onset Krabbe disease initially diagnosed as cerebroside sulfatase activator deficiency

Clinical and biochemical findings in a male subject with progressive encephalopathy and peripheral neuropathy are presented. Early development was normal. At age 3.5 years, he had seizures associated with fever. Subsequently, there was progressive neurologic deterioration. A CT brain scan at age 4 years, 2 months demonstrated multiple areas of variable density in the white matter. There was mild slowing of nerve conduction velocities and a sural nerve biopsy revealed segmental demyelinative neuropathy. Metachromatic leukodystrophy was suspected, but arylsulfatase A activity in leukocytes and fibroblasts was in the normal range. The cerebroside sulfate loading test on intact cultured fibroblasts showed attenuated hydrolysis leading to a tentative diagnosis of cerebroside sulfatase activator deficiency. However, the attenuated response of proband fibroblasts was not normalized by supplementation with activator in a reproducible manner, and urine showed hyperexcretion rather than deficiency of activator. Ultimately, an assay for galactosylceramide beta-galactosidase activity established a deficiency of this enzyme leading to the diagnosis of late-onset Krabbe disease.

Cerebroside-beta-glucosidase activity in Gaucher brain

Cerebroside-beta-glucosidase (acid beta-glucosidase) activity was determined in the forebrain from three patients with the infantile type of Gaucher disease, six patients with the Norrbottnian type and one patient with a mixed infantile/Norrbottnian type. The forebrain from ten subjects, aged 3 months to 20 years, served as controls. The activity was assayed with the natural substrate, (glucose-6-3H) nervonoylglucosylsphingosine and the artificial fluorogenic 4-methyl-umbelliferyl-beta-glucoside. The average residual activities of beta-glucosidase were 12% in the Norrbottnian type and 5% in the infantile type when determined with natural or artificial substrate. Optimum discrimination of the two types of Gaucher disease was obtained with the natural substrate.

Adult Niemann-Pick disease masquerading as sea blue histiocyte syndrome: report of a case confirmed by lipid analysis and enzyme assays

We present the clinical, pathologic, and metabolic findings of an adult woman with debilitating coronary artery disease and hepatosplenomegaly who was discovered to have multiorgan infiltration by sea blue histiocytes. A diagnosis of sea blue histiocyte (SBH) syndrome was made and no further workup performed. The patient suffered from progressive heart failure and sepsis following coronary artery bypass surgery and died 9 months after presentation. Tissues examined at autopsy showed pronounced infiltrates of both granular sea blue histiocytes and foamy, vacuolated histiocytes, which were morphologically compatible with Niemann-Pick cells. Ultrastructural examination of these cells revealed lamellar myelin-like figures as described in Niemann-Pick (N-P) disease. Fibroblast enzyme assay studies and liver lipid analyses performed after the patient's death revealed pronounced sphingomyelinase deficiency and a lipid profile diagnostic of N-P disease, type B. This case adds further support to the claim that some cases of apparent SBH syndrome actually represent a type of N-P disease.

Demonstration of human alpha-L-fucosidase polymorphism by means of monoclonal antibodies

Conventional rabbit antibodies and mouse monoclonal antibodies were raised to alpha-L-fucosidase purified from human placenta. Four monoclonal antibodies were studied, of which only one (A) was able to immunoprecipitate the fucosidase activity completely. Two antibodies (B and C) precipitated 65% and one (D) 35% of the activity. The enzyme precipitated by the monoclonal antibodies remained fully active, whereas the enzyme precipitated by conventional antibodies was partly inactivated. As shown by the method of successive immunoprecipitations, the monoclonal antibodies B and C recognized the same set of placental fucosidase molecules, and D a subset thereof. The purified fucosidase also yielded two components after gel electrophoresis in nondenaturing conditions, and the slower component corresponded to the set recognized by antibodies B and C. The fucosidase extracted from different tissues and serum was studied by immunoprecipitation. In all cases, the enzyme was completely precipitated by monoclonal antibody A. Two patterns were found with B, C and D: either part of the activity was precipitated by these antibodies (leucocytes, placenta, brain, liver, spleen, thymus) or B, C and D failed to precipitate any of the enzyme (serum, heart, kidney, testes).

An endogenous activator protein in human placenta for enzymatic degradation of glucosylceramide

An endogenous, heat-stable and pronase-sensitive activator for enzymatic hydrolysis of glucosylceramide was detected in the crude lysosome-mitochondria fraction of human placenta. Its properties differ distinctly in several important respects from those of the previously described glucosylceramidase activator. The activator reported here had no effect on crude glucosylceramidase with either glucosylceramide or 4-methylumbelliferyl-beta-D-glucopyranoside as the substrate in the presence of either sodium taurocholate or phosphatidylserine. On the contrary, glucosylceramide hydrolysis by the enzyme partially purified through Octyl-Sepharose 4B chromatography was stimulated by this activator 6-9-fold in the presence of either sodium taurocholate or phosphatidylserine. The Km for glucosylceramide in the presence of the activator was 1/3 of that without the activator. In the crude enzyme fraction, the activator was present in a 16-fold excess over the minimum amount necessary for full activation of the enzyme. Hydrolysis of the fluorogenic substrate by the post-Octyl-Sepharose enzyme, however, was not stimulated by the activator. Similarly, hydrolysis of galactosylceramide by galactosylceramidase obtained from the same Octyl-Sepharose chromatography was not stimulated. Our observations are consistent with the idea that glucosylceramidase is saturated by, or perhaps tightly associated with, this activator in the placenta and that they are dissociated by the Octyl-Sepharose chromatography. In fact, the properties of the combined post-Octyl-Sepharose enzyme and activator closely mimic those of the crude enzyme without added activator.

Fabry's disease with partially deficient hydrolysis of ceramide trihexoside

A report is presented on biochemical studies of the fibroblasts from a 26-year-old man with Fabry's disease whose clinical picture was atypical. The patient had severe pain in the extremities, but no angiokeratomas, corneal clouding or hypohidrosis. The trihexosylceramidase activity in the fibroblasts in vitro was deficient. The level and Km value of the residual activity were similar to levels seen in typical Fabry's patients. However, fibroblasts from the patient cultured in medium supplemented with [3H]ceramide trihexoside hydrolyzed the labeled ceramide trihexoside much higher than did cells from typical Fabry's patients, implying that the patient has a partial defect in hydrolysis of trihexosylceramide in cultured fibroblasts.