Molecular genetics of GM1β-galactosidase

Normal and Dysregulated Sphingolipid Metabolism: Contributions to Podocyte Injury and Beyond

Podocyte health is vital for maintaining proper glomerular filtration in the kidney. Interdigitating foot processes from podocytes form slit diaphragms which regulate the filtration of molecules through size and charge selectivity. The abundance of lipid rafts, which are ordered membrane domains rich in cholesterol and sphingolipids, near the slit diaphragm highlights the importance of lipid metabolism in podocyte health. Emerging research shows the importance of sphingolipid metabolism to podocyte health through structural and signaling roles. Dysregulation in sphingolipid metabolism has been shown to cause podocyte injury and drive glomerular disease progression. In this review, we discuss the structure and metabolism of sphingolipids, as well as their role in proper podocyte function and how alterations in sphingolipid metabolism contributes to podocyte injury and drives glomerular disease progression.

A Comprehensive Review: Sphingolipid Metabolism and Implications of Disruption in Sphingolipid Homeostasis

Sphingolipids are a specialized group of lipids essential to the composition of the plasma membrane of many cell types; however, they are primarily localized within the nervous system. The amphipathic properties of sphingolipids enable their participation in a variety of intricate metabolic pathways. Sphingoid bases are the building blocks for all sphingolipid derivatives, comprising a complex class of lipids. The biosynthesis and catabolism of these lipids play an integral role in small- and large-scale body functions, including participation in membrane domains and signalling; cell proliferation, death, migration, and invasiveness; inflammation; and central nervous system development. Recently, sphingolipids have become the focus of several fields of research in the medical and biological sciences, as these bioactive lipids have been identified as potent signalling and messenger molecules. Sphingolipids are now being exploited as therapeutic targets for several pathologies. Here we present a comprehensive review of the structure and metabolism of sphingolipids and their many functional roles within the cell. In addition, we highlight the role of sphingolipids in several pathologies, including inflammatory disease, cystic fibrosis, cancer, Alzheimer’s and Parkinson’s disease, and lysosomal storage disorders.

Rambam-Hasharon syndrome of psychomotor retardation, short stature, defective neutrophil motility, and Bombay phenotype

We describe 2 Arab patients, both offspring of unrelated consanguineous matings, with unusual facial appearance, severe mental retardation, microcephaly, cortical atrophy, seizures, hypotonia, dwarfism, and recurrent infections with neutrophilia. Neutrophil motility was markedly decreased but the opsonophagocytic activity was normal. Both patients lack the red blood cell (RBC) H antigen and manifest the Bombay (hh) phenotype. Familial endocardial fibroelastosis and familial tetralogy of Fallot segregated independently in one family. The occurrence of the same syndrome in 2 unrelated families suggests that the various aspects of the disorder are the pleiotropic effects of a single mutation. Homozygosity-by-descent for a deletion involving contiguous genes may explain the findings in this syndrome. Alternatively, a mutation which involves an ubiquitous GDP fucose donor rather than the enzyme (alpha 2-L-fucosyltransferase) or its substrate (glcNAc) may account for the pleiotropic manifestations in this syndrome.

Ocular histopathology and ultrastructure of Morquio syndrome (systemic mucopolysaccharidosis IV A)

Morquio syndrome (mucopolysaccharidosis IV) is a hereditary lysosomal storage disease characterized by dwarfism, spondyloepiphyseal and dental abnormalities, corneal opacification, and normal intelligence. We report the light and electron microscopic features of two patients with mucopolysaccharidosis type IV A (MPS IV A). Variable degrees of mucopolysaccharide deposition were seen in tissue surveyed by light microscopy. Transmission electron microscopy demonstrated fibrillogranular and multimembranous membrane-bound inclusions distributed primarily in the cornea and trabecular meshwork, to a milder degree in the conjunctiva and sclera, and rarely in the retinal pigment epithelium. Our findings indicate that the accumulation of mucopolysaccharide in MPS IV A occurs primarily in the structures of the anterior segment.

Diagnosis of subtypes of GM1 gangliosidosis in vitro and in vivo--using urinary oligosaccharides as substrates

In order to delineate clinical subtypes of GM1 gangliosidosis enzymologically, we prepared galactosyl oligosaccharides from the urine of patients, as substrates, and established the method of the galactosyl oligosaccharide beta-galactosidase assay. Galactosyl oligosaccharides beta-galactosidase activities (nmol/mg protein/20 h) in vitro, using substrates without repeating structures were; type 1, 1.0 +/- 0.5 (n = 6), type 2A, 2.1, type 2B, 3.4 +/- 0.7 (n = 5), type 3, 4.9 +/- 0.2 (n = 2). The activities in vitro using substrates with repeating structures were: type 1, 0.3 +/- 0.2 (n = 5), type 2A, 1.2, type 2B, 2.2 +/- 0.5 (n = 4), type 3, 4.2 +/- 0.3 (n = 2). The activities using substrates with and without repeating structures were affected in the fibroblasts of patients, and the residual activities in each subtype were reduced progressively with the increasing severity of the clinical features. The ratio between activities using substrates without repeating structures and activities using substrates with repeating structures indicated that beta-galactosidase activities toward Gal beta 1- of repeating structures were reduced progressively with the increasing severity of the clinical features. The activities in vivo (pmol/mg protein per 24 h) were: type 1, 11.8 +/- 1.8 (n = 2), type 2A, 24.8, type 2B, 40.0 +/- 9.7 (n = 2), type 3, 63.2. The activities in vivo were affected in the fibroblasts of patients and the residual activities were reduced in proportion to the severity of the clinical features. These differences of residual activities among each subtype make it possible to delineate clinical subtypes enzymologically.

Urinary screening for disorders of heteroglycan metabolism. Results of 10 years experience with a comprehensive system

The results of 10 years experience in urinary screening for disorders of heteroglycan metabolism are presented. Over 5,000 urines were analysed of which 216 were positive for excess mucopolysacchariduria. The enzymatic diagnosis was achieved in 159 mucopolysaccharidoses of which Type III Sanfilippo was the commonest (86 cases), followed by Type II Hunter (31 cases) and Type I Hurler (21 cases). A total of 27 urines were positive for excess oligosacchariduria, the enzymatic diagnosis being established in 20 cases. The most frequently encountered oligosaccharidosis was GM1 gangliosidosis (10 cases), followed by mannosidosis (5 cases). No cases of fucosidosis were found.

Progressive mental regression in siblings with Morquio disease type B (mucopolysaccharidosis IV B)

A brother and sister with clinical and radiological features of Morquio disease, but with atypical mental regression, are described. Leucocyte and fibroblast beta-galactosidase activity was deficient in the siblings, while N-acetylgalactosamine 6-sulphate sulphatase and neuraminidase were normal. Study of the residual fibroblast beta-galactosidase activity towards 4-methylumbelliferyl and p-nitrophenyl beta-D-galactosides indicated that the mutation resembles that in typical Morquio B disease (increased Km and similar pH maximum) rather than that in GM1-gangliosidosis. The patients have therefore been classified as having Morquio B disease with atypical mental regression rather than GM1-gangliosidosis variants with particularly severe bony abnormalities. The mutation was, however, distinct from that in Morquio B disease since residual activity towards the alternative artificial substrate 4-methylumbelliferyl-beta-D-fucoside was increased. The patients represent further examples of the heterogeneity that can result from mutation at the beta-galactosidase locus.

Inactivation of GM1-ganglioside beta-galactosidase by a specific inhibitor: a model for ganglioside storage disease

This study was designed to establish an in vitro model with biochemical and morphological similarities to the human neurodegenerative disease GM1 gangliosidosis. Utilizing a specific inactivator of the lysosomal enzyme GM1-ganglioside beta-galactosidase (beta-D-galactopyranosylmethyl-p-nitrophenyltriazene [beta-GalMNT]) and neuroblastoma X glioma hybrid cells (NG108-15), we suppressed beta-galactosidase activity for up to 72 hours. Coincidental with suppression of this enzyme to levels less than 1% of control, we found up to a nine-fold accumulation of its substrate, the GM1-ganglioside, and the ultrastructural appearance of membranous cytoplasmic bodies. beta-GalMNT treatment suppressed growth but had little effect on the specific activity of choline acetyltransferase, lactate dehydrogenase, or other lysosomal enzymes including galactosylceramidase. This model should permit studies of the neurophysiological effects of increased ganglioside accumulation and their reversibility.

Heterogeneity of Morquio disease

Further clinical heterogeneity of Morquio disease, mucopolysaccharidosis IV (MPS IV), is delineated by the observation of a 30-year-old man with unusually mild clinical manifestations. He is 156 cm tall, has comparatively mild skeletal abnormalities and fine corneal deposits. Keratosulfaturia is absent. N-Acetylgalactosamine-6-sulfate (GalNAc-6-S) sulfatase (E.C. 3.1.6.-) was markedly reduced in his fibroblasts. The residual enzyme activity exhibited a pH profile comparable to that of patients with the "classical" form of the disorder. From our observation and a review of the literature it is concluded that Morquio disease can be divided in several subgroups: besides the severe ("classical") type A there exist an intermediate and a mild form that are also caused by a GalNAc-6-S sulfatase deficiency. A late-onset variant of Morquio disease, which is due to a deficiency of beta-galactosidase, has been classified as type B. In addition, patients with mild manifestation of the disease and normal activities in fibroblasts of GalNAc-6-S sulfatase and beta-galactosidase have been observed (type C). The genetic nature of the broad clinical variability of Morquio disease is incompletely understood: it is partially caused by different enzyme defects. Other factors thought to influence the clinical expression include the pH profile of the residual enzyme activity and an additional neuraminidase defect.

Biosynthesis of the sulfatide/GM1 activator protein (SAP-1) in control and mutant cultured skin fibroblasts

Sphingolipid activator proteins (SAP) are relatively low-molecular-mass proteins that stimulate the hydrolysis of specific sphingolipids by the required lysosomal enzymes. SAP-1 or sulfatide/GM1 ganglioside activator protein has previously been demonstrated to stimulate the enzymatic hydrolysis of sulfatide, GM1 ganglioside and globotriaosylceramide. Using monospecific rabbit antibodies against human liver sulfatide/GM1 activator, the biosynthesis and processing of this activator were studied in cultured skin fibroblasts from controls and patients with GM1 gangliosidosis and a variant form of metachromatic leukodystrophy. When [35S]methionine was presented in the medium to control human fibroblasts for 4 h, the majority of the immunoprecipitable radiolabeling was confined to bands within three regions of apparent molecular mass 65-70, 35-52 and 8-13 kDa. The only immunoprecipitable radiolabeled species excreted into the medium when NH4Cl was present had an apparent molecular mass of 70 kDa. When the excretion products were given to fresh cells followed by incubation for up to 24 h there was production of the mature species. Treatment of the 70 kDa form with endoglycosidase F resulted in production of a 53 kDa molecular mass form. Pulse-chase experiments indicated that the initial immunoprecipitable translation product was 65 kDa which increased to 70 kDa over the next hour. The 65 kDa species must result from co-translational glycosylation of the polypeptide chain. Apparently, intralysosomal processing converts the 13 kDa form to the 8-11 kDa species. The cells from the patient with GM1 gangliosidosis could not process to the smallest species found in controls due to the deficiency of acid beta-galactosidase. Patients who have a variant form of metachromatic leukodystrophy do not make any immunoprecipitable radiolabeled products in the cells or in the media. This indicates a severe mutation in the gene coding for this activator protein. The production of such small mature species from a relatively large precursor form may regulate the production of this interesting protein.

Non-progressive psychomotor retardation in a child with severe deficiency of arylsulphatase A activity

Severe deficiency of arylsulphatase A (ARSA) activity was detected in a boy with delayed psychomotor development, coarse face and liver enlargement when he was aged 2. The case does not fit into the description of the Metachromatic leukodystrophy (MLD) proposed by Hagberg (1963) mainly because he did not deteriorate. Twelve years of follow up did not show any signs of decerebration or further intellectual decline; only speech was, and still is, absent. The reduced ARSA activity in leukocytes and fibroblasts of the father of the propositus suggests that he is heterozygote and that the ARSA deficiency of the propositus is inherited. The ARSA activity of the mother overlaps with the lowest control. The assumption that the mother is a carrier of different mutations could explain the discrepancy between the clinical and biochemical findings of the patient. This is a further family in which mutations other than the typical one can be postulated to explain variable clinical or biochemical pictures of MLD.

GM1 gangliosidosis, type 2: ocular clinicopathologic correlation

The clinical and pathological manifestations of a case of juvenile GM1 gangliosidosis are presented and the pathological findings compared with those previously reported for GM1 gangliosidosis in man and in animal models. The most striking finding in the present case was the marked degeneration of the retinal ganglion cell and nerve fiber layers. Although such extensive ganglion cell loss was not observed in any of the other cases reviewed, the presence of multimembranous inclusion bodies in retinal ganglion cells strongly suggests that the pathological process was similar in all cases. Much remains to be learned about the function of gangliosides in the healthy retina and about the pathophysiological consequences of deranged ganglioside metabolism. The many parallels, including those observed in pathological studies, between the human and animal forms of GM1 gangliosidosis allow an optimistic appraisal of the value of further research using the animal models.

Immunocytochemistry of lysosomal hydrolases and their precursor forms in normal and mutant human cells

The acid hydrolases alpha-glucosidase, beta-galactosidase, N-acetyl-beta-D-hexosaminidase, beta-glucocerebrosidase and cathepsin D were studied immunocytochemically in normal and mutant human cells using monoclonal and affinity-purified polyclonal antibodies. For light microscopy, Rhodamine or Fluorescein-labelled conjugates were used, and for electron microscopy protein A-gold conjugates were employed. With the double labelling procedure, it was found that in normal fibroblasts every lysosome contained all the enzymes studied. The method described also enabled us to demonstrate the presence or absence of mutant enzyme protein in fibroblasts derived from patients with a genetic lysosomal enzyme deficiency. Immunoreactive acid hydrolases or their precursor forms were found in the rough endoplasmic reticulum, the cisternae of the Golgi complex, Golgi associated vesicles and lysosomes. This is in agreement with the present concept that the Golgi complex plays an essential role in the processing and targeting of lysosomal enzymes.

Biochemical, immunological, and structural studies on a sphingolipid activator protein (SAP-1)

Sphingolipid activator protein-1 (SAP-1) is a glycoprotein found in human tissue extracts that stimulates the enzymatic hydrolysis of at least two glycosphingolipids, including GM1 ganglioside and sulfatide. The ability of purified SAP-1 to stimulate GM1 ganglioside hydrolysis by extracts of cultured fibroblasts from patients with beta-galactosidase deficiency was examined, and all patients had a pronounced deficiency (under 10% of control). Using monospecific antibodies against SAP-1, the concentration was determined in cultured fibroblasts by rocket immunoelectrophoresis. Extracts from 15 control cell lines were found to have 0.72 +/- 0.24 micrograms cross-reactive material/mg protein, while cell extracts from 8 patients with GM1 gangliosidosis involving mental retardation were found to have 1.08 +/- 0.17, which is significantly elevated. When the fibroblast extracts were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by electroblotting, multiple bands were observed. Controls were found to have two major bands with estimated molecular weights of 9000 and 9500, and a minor band at 7800. Extracts from patients with GM1 gangliosidosis were found to have multiple bands ranging upward to 13,000. Extracts from patients with the most severe clinical types of GM1 gangliosidosis had almost exclusively high-molecular-weight forms (molecular weights above 10,000). Treatment of SAP-1 from control liver with endoglycosidase D caused a decrease in the Mr 9500 band and increased in the Mr 7800 band. When SAP-1 from GM1 gangliosidosis liver was treated sequentially with neuraminidase, beta-galactosidase, and endoglycosidase D, almost all of it was converted to the forms found in control human liver.

Combined sialidase (neuraminidase) and beta-galactosidase deficiency. Clinical, morphological and enzymological observations in a patient

A patient with combined deficiency of sialidase and beta-galactosidase is described. This now 39-year-old man, who is of Japanese origin, showed gradually progressive clinical features from the age of six years. Many of these features are commonly found in sialidosis type 2 or in GM1-gangliosidosis. Both sialidase and beta-galactosidase activities were deficient in leucocytes and cultured fibroblasts. Leucocytes of his mother showed activities of both enzymes in the lower limit of the control range. Morphologically, the pattern of storage products in a skin biopsy resembled in many respects that seen in GM1-gangliosidosis. Moreover, storage products which could be typical of sialidosis were also observed. Since the patient showed angiokeratomata, the morphological findings were compared with those specific to Fabry's disease, but no similarities were found. An enzymological diagnosis of the disease is most reliable on cultured fibroblasts, discriminating it from sialidosis type 2 and GM1-gangliosidosis. In view of recent findings, leucocytes seem to be less suitable for the establishment of the diagnosis galactosialidosis.

Cerebral and visceral organ gangliosides and related glycolipids in gm1-gangliosidosis type 1, type 2 and chronic type

Biochemical analyses of the samples of GM1-gangliosidosis Type 1, Type 2, and Chronic type at autopsy showed that GM1 and asialo-GM1 are markedly increased in the whole cerebral tissues of patients with Type 1 and Type 2, but mainly in the basal ganglia including caudate nucleus and putamen in the Chronic Type as already reported by Kobayashi and Suzuki in 1981. On the other hand, the finding that the Type 1 visceral organs contained unusual glycolipids rather than gangliosides was contrasted to those of Type 2 which seemed less abnormal. The unusual glycolipids included particularly fucolipid I and II consisting of glucose:galactose:N-acetylglucosamine:fucose (1:2:1:1) and (1:3:2:2), respectively. The chemical structure of oligosaccharide moiety of fucolipid I may be identical with Lacto-N-fucopentaose II or Lacto-N-fucopentaose III. The fucolipid II may be proposed to be Lacto-N-difucooctanose.

Morquio B syndrome: a primary defect in beta-galactosidase

Fibroblasts from patients with Morquio B syndrome contain normal numbers of beta-galactosidase molecules with normal turnover but strongly reduced activity per enzyme molecule. Various substrate affinities are abnormal: the Km for methylum belliferyl (MU)-beta-galactoside is 4-10-fold elevated and affinity for keratan sulphate and oligosaccharides, isolated from Morquio B urine, was not detectable. In contrast, these substrate affinities are normal for beta-galactosidase in adult type GM1-gangliosidosis fibroblasts. Cell hybridization studies demonstrate that Morquio B syndrome and infantile and adult type GM1-gangliosidosis belong to the same complementation group. From these results we conclude that Morquio B syndrome is caused by a mutation in the structural gene for beta-galactosidase, which is allelic to the mutations in infantile and adult type GM1-gangliosidosis. Urinary excretion of keratan sulphate and oligosaccharides is abnormal in Morquio B syndrome but normal in adult type GM1-gangliosidosis. The catalytic properties of beta-galactosidase in Morquio B syndrome and GM1-gangliosidosis provide a possible explanation for the distinct clinical manifestations in these disorders.

Human beta-galactosidase and alpha-neuraminidase deficient mucolipidosis: genetic complementation analysis of the neuraminidase deficiency

Human beta-galactosidase and alpha-neuraminidase deficient mucolipidosis [ML(gal-neur-)] is an inherited lysosomal enzymopathy which recently was designated as a sialidosis. We analyzed the neuraminidase deficiency of this disorder with genetic complementation analyses using a heterokaryon enrichment procedure. The genetic defects of two apparent variants of this disorder complemented the defects of the neuraminidase deficiency diseases, sialidosis I and mucolipidosis I, resulting in the restoration of neuraminidase activity in heterokaryons. The neuraminidase deficiency, therefore, may not be the primary defect in ML(gal-neur-) and is not an appropriate test for determining carrier status. The clinical and biochemical characteristics of this disorder suggest that a post-translational or processing event for these enzymes may be defective. The defect, however, is different from I-cell disease and pseudo-Hurler polydystrophy, two disorders of post-translational lysosomal enzyme biosynthesis, since complementation studies demonstrated recovery of intracellular beta-galactosidase and alpha-neuraminidase levels in heterokaryons. The lack of human beta-galactosidase expression in man-mouse somatic cell hybrids formed from fibroblasts of the infantile onset type disorder suggests that the defect is not corrected by the mouse genome. The ML(gal-neur-) disorder therefore appears to be a distinct subtype of the inherited neuraminidase deficiencies in which the defect mat occur in a post-translational or regulatory step which coordinately affects the expression of lysosomal beta-galactosidase and alpha-neuraminidase.

GM1 gangliosidosis: enzymatic variation in a single family

Acid beta-galactosidase activity can be separated into multiple molecular forms by isoelectric focusing on cellulose acetate membranes. The residual acid beta-galactosidase in the juvenile form of GM1 gangliosidosis has three bands of enzyme activity with an apparent isoelectric pH (pI) range from 4.9 to 5.2, whereas that in the infantile form has a single band with an apparent pI of 5.2. Separation of residual acid beta-galactosidase into multiple molecular forms by analytical isoelectric focusing demonstrates enzymatic differences that can be correlated with the allelic mutations that affect the GM1 ganglioside beta-galactosidase locus.

GM1 gangliosidosis: phenotypic variation in a single family

Infantile, juvenile, and adult forms of GM1 gangliosidosis have been well characterized. Certain genetic and biochemical studies have suggested that the phenotypic variation found in GM1 gangliosidosis results from different allelic mutations affecting the GM1 ganglioside beta-galactosidase locus and that different combinations of these mutations accounts for the clinical heterogeneity of this illness. A family in which both the infantile and juvenile forms of GM1 gangliosidosis occurred, the children sharing a common mutation of their acid beta-galactosidase activity, supports the allelic nature of these different clinical forms of the disease. From the observations made in this unique family, additional phenotypes of GM1 gangliosidosis might be anticipated.

Electron microscopy: a method for the diagnosis of inherited metabolic storage diseases. Electron microscopy in diagnosis

In the diagnosis of inherited metabolic diseases, electron microscopy has become an important method complementary to clinical, histological and biochemical assays. The characteristic ultrastructure of stored material as well as the site of accumulation in the cell are shown in a number of metabolic disorders. The most prominent advantages of electron microscopical techniques as compared to alternative techniques are discussed. One of the advantages is the fact that ultrastructural investigation requires only tissue samples of very small size, and another that its results may be obtained within two days. Moreover, transmission electron microscopy permits new and promising analytical methods such as quantitative estimation of organellar changes (morphometry) and energy dispersive X-ray elemental analysis (EDX).

Adult GM1 gangliosidosis: clinical and biochemical studies on two patients and comparison to other patients called variant or adult GM1 gangliosidosis

Two young adult siblings were diagnosed as having a deficiency of acid beta-galactosidase activity in leukocytes and fibroblasts. The parents had enzyme levels approximately half of the normal level, consistent with this being the primary enzymatic lesion. Sialidose activities measured with natural and synthetic substrates in the patient's skin fibroblast cultures were normal. Hybridization of one of these patient's cells with cells from a patient with GM1 gangliosidosis, Type 1 did not show complementation of beta-galactosidase activity. However, when the cells from the patient were hybridized with cells from a patient with combined sialidase and beta-galactosidase deficiency, complementation was observed. These two siblings have ataxia, mild intellectual deterioration, slurred speech, mild vertebral changes and little, if any, visceromegaly. They do not have myoclonus, seizures or cherry-red spots, which are found in most patients with combined sialidase and beta-galactosidase deficiency. These patients are discussed with regard to other patients in the literature called variant or adult GM1 gangliosidosis.

Beta-galactosidase deficiency: studies of two patients with prolonged survival

Two adults with beta-galactosidase deficiency were studied. Differences in a number of beta-galactosidase parameters (pH optima, heat denaturation, NaCl kinetics) were noted between the patients. Differences were also noted in beta-galactosidase electrophoretic mobilities and urinary oligosaccharides; however, there was no complementation in cell fusion studies. It is suggested that these two patients have different primary mutations at the beta-galactosidase locus which are probably structural in nature.

The specificity of beta-galactosidase in the degradation of gangliosides

Available evidence indicates that a least two genetically distinct acidic lysosomal beta-galactosidases are present in mammalian tissues. One of them, galactosylceramidase, is primarily responsible for degradation of galactosylceramide, galactosylsphingosine, and monogalactosyl-diglyceride, while the other, GM1-ganglioside beta-galactosidase, degrades GM1-ganglioside and asialo GM1-ganglioside. Lactosylceramide can be hydrolyzed by either of the two enzymes. These substrate specificities of the two beta-galactosidases can adequately explain the known findings in the two genetic beta-galactosidase deficiency diseases. The possibilities of the specific lactosylceramidase have not yet received the necessary independent confirmation.

Basic findings and current developments in sphingolipidoses

Sphingolipidoses are caused by recessively inherited deficiencies of lysosomal hydrolases. The clinical backgrounds of and current biochemical and genetic approaches to the different forms and variants of gangliosidoses, trihexosylceramidosis (Fabry's disease), galactosylceramidosis (Krabbe's disease), sulfatidoses (metachromatic leukodystrophies), glucosylceramidosis (Gaucher's disease), sphingomyelinoses (Niemann-Pick disease) and ceramidosis (Farber's disease) are presented.

GM1-gangliosidosis: chromosome 3 assignment of the beta-galactosidase-A gene (beta GALA)

The structural gene (beta GALA) coding for lysosomal beta-galactosidase-A (EC 3.2.1.23) has been assigned to human chromosome 3 using man--mouse somatic cell hybrids. Human beta-galactosidase-A was identified in cell hybrids with a species-specific antiserum to human liver beta-galactosidase-A. The antiserum precipitates beta-galactosidase-A from human tissues, cultured cells, and cell hybrids, and recognizes cross-reacting material from a patient with GM1 gangliosidosis. We have analyzed 90 primary man--mouse hybrids derived from 12 separate fusion experiments utilizing cells from 9 individuals. Enzyme segregation analysis excluded all chromosomes for beta GALA assignment except chromosome 3. Concordant segregation of chromosomes and enzymes in 16 cell hybrids demonstrated assignment of beta GALA to chromosome 3; all other chromosomes were excluded. The evidence suggests that GM1 gangliosidosis is a consequence of mutation at this beta GALA locus on chromosome 3.

Affinity chromatography and separation of the molecular forms of monkey brain alpha-L-fucosidase on fucose-linked sepharose

A simple affinity system which required coupling of alpha-L-fucose to Sepharose 4B by epichlorohydrin treatment of Sepharose 4B in the presence of alpha-L-fucose under alkaline conditions has been described. A partially purified preparation of monkey brain alpha-L-fucosidase (alpha-L-fucoside fucohydrolase, EC 3.2.1.51) was resolved at pH 5.0 into two major fractions: one bound and one retarded. The enzyme bound to the affinity column and specifically eluted by 2 mM alpha-L-fucose at pH 5.0 appeared to be homogeneous by polyacrylamide gel electrophoresis and was constituted mainly by the tetrameric form of the enzyme. The enzyme fraction retarded by the affinity column was found to contain mainly the monomeric form of the enzyme. Additional evidence for the different molecular forms of the enzyme in the bound and retarded fractions came from pH activity profiles and heat inactivation studies. The fucose-Sepharose appeared to bind the tetrameric form of the enzyme specifically and, further, alpha-L-fucose helped to retain the molecular integrity of the tetrameric enzyme.

A two-year-old patient with an atypical expression of GM1-beta-galactosidase deficiency: biochemical, immunological, and cell genetic studies

Cultured skin fibroblasts from a 2-year-old boy with an atypical form of beta-galactosidase deficiency have been studied. With the artificial substrate 4-methylumbelliferyl-beta-D-galactopyranoside, 5--15% residual activity was found in fibroblasts from this patient. Most of this activity was in the monomeric A form of the enzyme, very little in the multimeric B form. Km value, pH profile, and heat lability of the mutant enzyme were similar to those of beta-galactosidase from control fibroblasts. Immunological studies showed that the mutant enzyme cross-reacted with an antiserum raised against human liver beta-galactosidase, but the catalytic activity per unit antigenic activity was lower than normal. It was demonstrated by somatic cell hybridization that the gene mutation in this patient is different from that in patients with type 1 or type 2 GM1-gangliosidosis. No genetic complementation was found after fusion of fibroblasts from this patient with those from two other clinical variants of GM1-gangliosidosis formerly designated type 3 and adult type 4.

Biochemistry and genetics of gangliosidoses

The gangliosidoses comprise an-ever increasing number of biochemically and phenotypically variant diseases. In most of them an autosomal recessive inherited deficiency of a lysosomal hydrolase results in the fatal accumulation of glucolipids (predominantly in the nervous tissue) and of oligosaccharides. The structure, substrate specificity, immunological properties of and genetic studies on the relevant glycosidases, ganglioside GM1 beta-galactosidase and beta-hexosaminidase isoenzymes, are reviewed in this paper. Contrary to general expectation, only a poor correlation is observed between the severity of the disease and residual activity of the defective enzyme when measured with synthetic or natural substrates in the presence of detergents. For the understanding of variant diseases and for their pre- and postnatal diagnosis, the necessity of studying the substrate specificity of normal and mutated enzymes under conditions similar to the in vivo situation, e.g., with natural substrates in the presence of appropriate activator proteins, is stressed. The possibility that detergents may have adverse affects on the substrate specificity of the enzymes is discussed for the beta-hexosaminidases. The significance of activator proteins for the proper interaction of lipid substrates and water-soluble hydrolases is illustrated by the fatal glycolipid storage resulting from an activator protein deficiency in the AB variant of GM2-gangliosidosis. Recent somatic complementation studies have revealed the existence of a presumably post-translational modification factor necessary for the expression of ganglioside GM1 beta-galactosidase activity. This factor is deficient in a group of variants of GM1-glangliosidosis. Among the possible reasons for the variability of enzyme activity levels in heterozygotes and patients, allelic mutations, formation of hybrid enzymes, and the existence of patients as compound heterozygotes are discussed. All these may result in the production of mutant enzymes with an altered specificity for a variety of natural substrates.

The cherry red spot-myoclonus syndrome: a newly recognized inherited lysosomal storage disease due to acid neuraminidase deficiency

A newly discovered lysosomal storage disorder, apparently transmitted as an autosomal recessive trait, presents with cherry red spots in childhood, progressive debilitating myoclonus, insidious visual loss, and normal intelligence. Somatic and bony abnormalities are not evident clinically. Neuronal lipidosis and vacuolated Kuppfer cells are found upon tissue examination. The diagnosis can be most easily confirmed by chromatographic screening for urinary sialyloligosaccharides. The primary enzyme defect is a deficiency of an acid neuraminidase isoenzyme which cleaves sialyloligosaccharides. I discuss here the clinical phenotype in four patients, the chemical abnormality, the pathogenesis, the enzyme defect and the molecular genetics of this disorder.

Sialidase (alpha-n-acetyl neuraminidase) deficiency: the enzyme defect in an adult with macular cherry-red spots and myoclonus without dementia

A 31-year-old male is described who has macular cherry-red spots, increased deep tendon reflexes and and myoclonus without dementia. An older brother died at age 33 of a disease with similar symptomatology. Homogenates of cultured fibroblasts from the patient exhibited 2.6, 8.1 and 12.4% of normal mean sialidase (neuraminidase, N-acetyl-neuraminosyl glycohydrolase, EC 3.21.18) activity, respectively, against 2-(3'-methoxyphenyl)-N-acetyl-alpha-neuraminic acid, N-acetyl-neuramin-lactose and fetuin. Activities of 14 other lysosomal enzymes were within the range of normal control fibroblasts. The sialidase activities in fibroblasts from the patient's parents and children were 30 to 67% of normal. It is concluded that this is the first proven case of a new autosomal recessive disorder resulting in cherry-red spots, myoclonus and a sialidase deficiency.

Beta-galactosidase deficiency: prolonged survival in three patients following early central nervous system deterioration

Three adult patients from two families have shown slowly progressive neurologic deterioration since the age of 3 years, associated with profound beta-galactosidase deficiency. Although affected individuals from the two different families differ in degree of intellectual deficit, facial coarseness and spondyloepiphyseal dysplasia, all lack visceromegaly and macular red spots. The diversity of phenotypic expression in these patients and others previously reported suggests the existence of composite genotypes (compound and double heterozygosity).

Glycosphingolipid hydrolases: properties and molecular genetics

This is a review of the properties and molecular genetics of six lysosomal hydrolases: beta-galactosidase, hexosaminidases A and B, alpha-galactosidase, beta-glucosidase and alpha-fucosidase. Each enzyme is discussed with regards to isoenzymes and substrate specificity, subunit structure, genetic relationship of isoenzymes and genetic variants. The molecular genetics of human diseases caused by deficiencies of each enzyme are discussed.

Regional localization of a beta-galactosidase locus on human chromosome 22

Human white blood cells with an X/22 translocation [46, XX, t(X;22)(q23;q13)] were fused with Chinese hamster cells. The isolated hybrids were analyzed for human chromosomes and 21 enzyme markers. An electrophoretic technique for studying the beta-galactosidase isoenzymes in man-Chinese hamster hybrid cells was developed. Immunological studies showed that the beta-galactosidase marker studied in these hybrids did contain immunological determinants of human origin. Furthermore the results provided evidence that a locus for beta-galactosidase is situated on chromosome 22 distal to the breakpoint in q13.

Isolated acid neuraminidase deficiency: a distinct lysosomal storage disease

An 8-month-old female presented with coarse facies and hepatosplenomegaly at birth. Growth proceeded at an accelerated rate and mental development was normal. A pattern of dysostosis multiplex developed radiographically. Cytoplasmic inclusions consistent with lysosomal storage disease were demonstrated by electron microscopy in bone marrow, liver, and cartilage cells and in cultured skin fibroblasts. Assays of the fibroblasts revealed a specific deficiency of acid neuraminidase and 6-fold increase in intracellular bound sialic acid. An unidentified macromolecular compound rich in sialic acid was excreted in excessive amounts in the urine. The phenotype suggests defective degradation primarily of glycoproteins and possibly to a lesser extent of keratan sulfate and gangliosides.