Adult GM1 Gangliosidosis Research Articles

GM1 Gangliosidosis Revealed by Fetoplacental Hydrops Syndrome: A Case Report

GM1 gangliosidos is describes a family of disorders that result from deficient activity of the lysosomal hydrolase, β-galactosidase, and which manifest varying degrees of neurodegeneration, retinal cherry-red spots, and visceromegaly. The three traditional subgroups of infantile, juvenile, and adult GM1 gangliosidosis show phenotypic overlap, although in general, the earlier the onset, the more severe the manifestations. This article gives an overview of the clinical signs in a patient with GM1 type 1 gangliosidosis revealed by fetoplacental hydrops syndrome.

Clinical findings in Brazilian patients with adult GM1 gangliosidosis.

GM1 gangliosidosis is a lysosomal storage disorder caused by β‐galactosidase deficiency. To date, prospective studies for GM1 gangliosidosis are not available, and only a few have focused on the adult form. This retrospective cross‐sectional study focused on clinical findings in Brazilian patients with the adult form of GM1 gangliosidosis collected over 2 years. Ten subjects were included in the study. Eight were males and two females, with median age at diagnosis of 11.5 years (IQR, 4‐34 years). Short stature and weight below normal were seen in five out of the six patients with data available. Radiological findings revealed that the most frequent skeletal abnormalities were beaked vertebrae, followed by hip dysplasia, and platyspondyly. Neurological examination revealed that dystonia and swallowing problems were the most frequently reported. None of the patients presented hyperkinesia, truncal hypertonia, Parkinsonism, or spinal cord compression. Clinical evaluation revealed impairment in activities of cognitive/intellectual development and behavioral/psychiatric disorders in all nine subjects with data available. Language/speech impairment (dysarthria) was found in 8/9 patients, fine motor and gross motor impairments were reported in 7/9 and 5/9 patients, respectively. Impairment of cognition and daily life activities were seen in 7/9 individuals. Our findings failed to clearly identify typical early or late alterations presented in GM1 gangliosidosis patients, which confirms that it is a very heterogeneous condition with wide phenotypic variability. This should be taken into account in the evaluation of future therapies for this challenging condition.

The treatment of juvenile/adult GM1-gangliosidosis with Miglustat may reverse disease progression.

Juvenile and adult GM1-gangliosidosis are invariably characterized by progressive neurological deterioration. To date only symptomatic therapies are available. We report for the first time the positive results of Miglustat (OGT 918, N-butyl-deoxynojirimycin) treatment on three Italian GM1-gangliosidosis patients. The first two patients had a juvenile form (enzyme activity ≤5%, GLB1 genotype p.R201H/c.1068+1G>T; p.R201H/p.I51N), while the third patient had an adult form (enzyme activity about 7%, p.T329A/p.R442Q). Treatment with Miglustat at the dose of 600mg/day was started at the age of 10, 17 and 28years; age at last evaluation was 21, 20 and 38 respectively. Response to treatment was evaluated using neurological examinations in all three patients every 4-6months, the assessment of Movement Disorder-Childhood Rating Scale (MD-CRS) in the second patient, and the 6-Minute Walking Test (6-MWT) in the third patient. The baseline neurological status was severely impaired, with loss of autonomous ambulation and speech in the first two patients, and gait and language difficulties in the third patient. All three patients showed gradual improvement while being treated; both juvenile patients regained the ability to walk without assistance for few meters, and increased alertness and vocalization. The MD-CRS class score in the second patient decreased from 4 to 2. The third patient improved in movement and speech control, the distance covered during the 6-MWT increased from 338 to 475m. These results suggest that Miglustat may help slow down or reverse the disease progression in juvenile/adult GM1-gangliosidosis.

Systemic AAV9 gene transfer in adult GM1 gangliosidosis mice reduces lysosomal storage in CNS and extends lifespan.

GM1 gangliosidosis (GM1) is an autosomal recessive lysosomal storage disease where GLB1 gene mutations result in a reduction or absence of lysosomal acid β-galactosidase (βgal) activity. βgal deficiency leads to accumulation of GM1-ganglioside in the central nervous system (CNS). GM1 is characterized by progressive neurological decline resulting in generalized paralysis, extreme emaciation and death. In this study, we assessed the therapeutic efficacy of an adeno-associated virus (AAV) 9-mβgal vector infused systemically in adult GM1 mice (βGal(-/-)) at 1 × 10(11) or 3 × 10(11) vector genomes (vg). Biochemical analysis of AAV9-treated GM1 mice showed high βGal activity in liver and serum. Moderate βGal levels throughout CNS resulted in a 36-76% reduction in GM1-ganglioside content in the brain and 75-86% in the spinal cord. Histological analyses of the CNS of animals treated with 3 × 10(11) vg dose revealed increased presence of βgal and clearance of lysosomal storage throughout cortex, hippocampus, brainstem and spinal cord. Storage reduction in these regions was accompanied by a marked decrease in astrogliosis. AAV9 treatment resulted in improved performance in multiple tests of motor function and behavior. Also the majority of GM1 mice in the 3 × 10(11) vg cohort retained ambulation and rearing despite reaching the humane endpoint due to weight loss. Importantly, the median survival of AAV9 treatment groups (316-576 days) was significantly increased over controls (250-264 days). This study shows that moderate widespread expression of βgal in the CNS of GM1 gangliosidosis mice is sufficient to achieve significant biochemical impact with phenotypic amelioration and extension in lifespan.

Clinical Findings and Natural History in Ten Unrelated Families with Juvenile and Adult GM1 Gangliosidosis.

We describe 12 subjects of ten unrelated families from the region of Campinas and the southern state of Minas Gerais, Brazil, who presented with juvenile (n = 4) and adult (n = 8) GM1 gangliosidosis. Data includes clinical history, physical examination, and ancillary exam findings. Six subjects presented initially with skeletal deformities, while the remaining six had neurological manifestations at onset. Over time, all exhibited a combination of osteoarticular and neurologic degeneration with varying degrees of severity. Corneal clouding, angiokeratomas, and inguinal hernia were seen in one individual each. Other features commonly described in lysosomal storage disorders were not found in this series, such as coarse faces, gingival hypertrophy, visceromegaly, and cherry red spot. All subjects presented with short stature, dysostosis multiplex, dysarthria, and impairment of activities of daily living, 10/12 had extrapyramidal signs, 8/12 had pyramidal signs, 8/12 had oculomotor abnormalities, 4/12 had behavioral alterations, and 2/12 had ataxia. None had seizures or Parkinsonism. All female subjects developed severe hip dysplasia and underwent arthroplasty due to chronic pain. A vertebral bone bar and os odontoideum, not previously described in this condition, were found in one patient each. There was no clear genotype-phenotype correlation regarding enzyme residual activity and clinical findings, since all subjects were compound heterozygous, but the p.T500A was the most frequent allele in eight families and was associated to Morquio B phenotype. Two sets of siblings allowed intrafamilial comparison revealing consistent features among the families. Interfamilial correlation among unrelated families presenting the same mutations was less consistent.

Mechanisms of distribution of mouse β-galactosidase in the adult GM1-gangliosidosis brain

GM1-gangliosidosis is a lysosomal storage disease (LSD) caused by an autosomal recessive deficiency of lysosomal acid beta-galactosidase (betagal). This leads to accumulation of GM1-ganglioside and its asialo derivative GA1 in the central nervous system (CNS), and progressive neurodegeneration. Therapeutic AAV-mediated gene delivery to the brain for LSDs has proven very successful in several animal models. GM1-gangliosidosis is also a prime candidate for AAV-mediated gene therapy in the CNS. As global neuropathology characterizes the most severe forms of this disease, therapeutic interventions need to achieve distribution of betagal throughout the entire CNS. Therefore, careful consideration of routes of administration and target structures from where metabolically active enzyme can be produced, released and distributed throughout the CNS, is necessary. The goal of this study was to investigate the pattern and mechanism of distribution of betagal in the adult GM1-gangliosidosis mouse brain upon hippocampal injection of an AAV vector-encoding betagal. We found evidence that three different mechanisms contribute to its distribution in the brain: (1) diffusion; (2) axonal transport within neurons from the site of production; (3) CSF flow in the perivascular space of Virchow-Robin. In addition, we found evidence of axonal transport of vector-encoded mRNA.

The potential action of galactose as a “chemical chaperone”: Increase of beta galactosidase activity in fibroblasts from an adult GM1-gangliosidosis patient

Background The glycosphingolipid storage disorder GM1-gangliosidosis is a severe neurodegenerative condition for which no therapy is currently available. Protein misfolding in lysosomal defects may have the potential to be corrected by chemical chaperones: in vitro and clinical approaches are being investigated. Aims We investigated the in vitro effect of galactose on some lysosomal hydrolases, and its in vitro efficacy as a chemical chaperone in GM1-gangliosidosis. Methods Galactose was added to the culture medium of fibroblasts from patients, controls and transfected COS-1 cells. Enzyme assays of lysosomal hydrolases, beta galactosidase in particular, were performed. Results Our data show that galactose alters selectively alpha and beta galactosidases. A significant increase (2,5 fold) in beta galactosidase activity occurred when galactose was added to the cultured fibroblasts of an adult patient. Chemical chaperone therapy requires the presence of residual enzyme activity. The adult patient here reported is heterozygous for the p.T329A mutation that showed no beta galactosidase activity, and for the p.R442Q mutation with residual enzyme activity. The p.R442Q mutation was therefore selected as a potential target for the galactose chaperone; after the addition of galactose, COS-1 cells transfected with this mutation showed an increase in beta galactosidase activity from 6.9% to 12% of control values. Conclusions These results suggest that galactose or its derivatives with potential chaperone properties could be used in the development of non-invasive therapies for GM1-gangliosidosis.

409. Complete Correction of Enzymatic Deficiency and Lysosomal Storage throughout the Brain in a Mouse Model of GM1-gangliosidosis after Neonatal Intracerebroventricular Injection of an AAV1 Vector Encoding Lysosomal Acid Beta- galactosidase

GM1 gangliosidosis is a glycosphingolipid (GSL) lysosomal storage disease caused by autosomal recessive deficiency of lysosomal acid |[beta]|-galactosidase (|[beta]|gal). This disease is characterized by accumulation of GM1-ganglioside and its asialo-form (GA1) in the CNS. In this study we examined the effect of neonatal intracerebroventricular injection of an adeno-associated virus (AAV) vector (serotype 1) encoding mouse |[beta]|gal under control of a CBA promoter (AAV1-CBA-|[beta]|gal), on bgal enzyme activity and brain GSL content in adult GM1 gangliosidosis (|[beta]|gal-/-) mice. A total of 4 |[mu]|l of AAV1-CBA-|[beta]|gal vector with a titer of 4.3x1013 gc/mL was injected into the lateral ventricles (2 |[mu]|l each) of P0 |[beta]|gal-/- mice. At 3 months we analyzed one brain hemisphere for enzyme distribution by X-gal staining at pH 5.0. |[beta]|gal was expressed throughout the brain at higher levels than those found in wild type controls or untreated |[beta]|gal-/- mice. The highest levels of enzymatic activity were associated with allocortical areas such as the hippocampal formation and olfactory bulb, and periallocortical areas. Five regions in the other hemisphere were analyzed for enzymatic activity and GSL content. AAV1-treated |[beta]|gal-/- mice presented enzymatic activities between 7- and 65-fold higher (depending on the region) than in wild type controls. Total brain ganglioside and GM1 content (|[mu]|g of sialic acid/100 mg dry weight) was reduced from 824 |[plusmn]| 65 |[mu]|g and 476 |[plusmn]| 42 |[mu]|g in non-treated |[beta]|gal -/- mice to 444 |[plusmn]| 21 |[mu]|g and 46.9 |[plusmn]| 2.1 |[mu]|g in AAV1-treated |[beta]|gal -/- mice, respectively. These GSL values in treated mice were statistically identical to those measured in wild type controls (412 |[plusmn]| 17 |[mu]|g and 53.2 |[plusmn]| 1.1 |[mu]|g, respectively). Furthermore, GA1 storage was completely eliminated. Thus GSL levels in the brains of AAV-treated |[beta]|gal-/- mice were restored to normal levels. Analysis of GM1-ganglioside storage in the brain by staining with subunit B of cholera toxin (CTX-B) showed that AAV-treated |[beta]|gal-/- mice were identical to wild type controls. Interestingly, fiber tracts in untreated |[beta]|gal-/- mice stained weakly with CTX-B or not at all. This may be the mouse equivalent of delayed myelination reported in type I GM1-gangliosidosis in humans and dogs. Filipin staining of brains for unesterified cholesterol, which accumulates in the brain in glycosphingolipidoses, showed that AAV1-treated |[beta]|gal-/- mice were indistinguishable from wild type mice, while untreated |[beta]|gal-/- mice displayed strong storage throughout the brain. Altogether the biochemical and histological evidence in this study show that brain metabolism in AAV-treated |[beta]|gal-/- mice was normal. Thus we conclude that neonatal AAV- mediated gene delivery of lysosomal acid |[beta]|-galactosidase to the brain is an effective approach for treatment of GM1 gangliosidosis.

961. AAV1-Mediated Gene Delivery to the Adult GM1-Gangliosidosis Mouse Hippocampus Leads to Marked Reduction in Storage in Physically and Synaptically-Connected Areas of the Brain

GM1-gangliosidosis is a lysosomal storage disease caused by an autosomal recessive deficiency of lysosomal acid beta-galactosidase (b-gal) leading to accumulation of GM1-ganglioside in the central nervous system, and often accompanied by severe mental retardation. Knock-out mouse models (GM1 KO) of this disease mimic the biochemical findings in humans, with absence of b-gal activity and extensive GM1-ganglioside storage throughout the brain. The experiments reported here were conducted to: 1) Investigate the efficiency of adeno-associated virus (AAV) vector-mediated delivery of mouse b-gal to the GM1 KO mouse brain; 2) Characterize the mechanisms by which this enzyme is distributed in the brain from the injection site; 3) Evaluate the therapeutic potential of this strategy by its ability to decrease GM1-ganglioside storage. The AAV vectors used in this study, AAV-CBA-MBG-W (mouse b-gal) and AAV-CBA-GFP-W (GFP), carry AAV2 ITRs, a CBA promoter to control transgene expression, a WPRE element, and a BGH polyA signal. One l of each virus stock was infused stereotaxically into the left hippocampus of 6 weeks old GM1 KO mice by convection-enhanced delivery (CED) at 0.1 l.min-1. One month later the brains were analyzed for b-gal expression by X-gal staining at pH 4.5, GFP expression in control mice, and GM1-ganglioside storage levels by immunofluorescence with an anti-GM1 ganglioside antibody. In mice injected with AAV-CBA-MBG-W, the ipsilateral hippocampus showed robust X-gal staining in most structures, while in the contralateral hippocampus staining was evident in the CA1-CA3 oriens, pyramidal, and radiatum layers, and the granule cell layer of the dentate gyrus (DG). Strong X-gal staining was also evident in the overlying ipsilateral cortex, while there was no apparent staining in the contralateral cortex. No X-gal staining was evident in control mice injected with GFP-encoding vector. In these mice there was strong GFP expression in the granule and pyramidal cell layer of the ipsilateral DG and CA3, respectively, and in the CA1-CA3 oriens and radiatum layers in both hemispheres. The Ipsilateral hippocampus in AAV-CBA-MBG-W injected mice was completely devoid of GM1-ganglioside storage while in the contralateral hippocampus there was a significant decrease in storage in the CA1-CA3 pyramidal layer and granule cell layer of the DG. A significant reduction in storage was also observed in the ipsilateral overlying cortex. In mice injected with the GFP-encoding vector there was strong storage in the CA1-CA3 pyramidal layer, granule cell layer of the DG, and cortex.

Clinical features of adult GM1 gangliosidosis: Report of three Indian patients and review of 40 cases

Deficiency of enzyme acid beta-galactosidase causes GM1 gangliosidosis. Patients with adult GM1 gangliosidosis typically present with generalized dystonia. We describe clinical, bone marrow, and radiological features of adult GM1 gangliosidosis to help improve its recognition. We report 3 Indian patients and review of reports between 1981 and October 2002. The disease frequently is reported in the Japanese literature (75%). Patients are normal at birth and have normal early motor and mental development. Onset is within the first decade with abnormal gait, or worsening of speech is an initial symptom. Dystonia occurs in 97% of patients. Facial dystonia described as "facial grimacing" observed in approximately 90% could be an important clinical clue. Dysarthria/anarthria (97%) is frequent, and eye movements are normal. Bone marrow examination may show Gaucher-like foam cells (39%). Magnetic resonance imaging (MRI) frequently (90.9%) shows bilateral symmetrical putamenal hyperintensities on T2-weighted and proton density images. Diagnosis is confirmed by demonstrating deficiency of beta-galactosidase. Adult (Type 3) GM1 Gangliosidosis commonly presents with generalized dystonia with prominent facial dystonia, severe speech disturbances, and normal eye movements. Bone marrow frequently shows Gaucher-like foam cells. MRI shows typical lesions in the putamen. Deficiency of beta-galactosidase in fibroblasts confirms the diagnosis.

GM1 gangliosidosis type 3 with severe jaw-closing impairment

The patient had adult GM1 gangliosidosis (type 3) with severe impairment of mastication caused by dystonia of anterior digastric muscles (jaw-opener) on clenching. This is the first report on jaw dystonia severe enough to cause the masticatory impairment in adult GM1 gangliosidosis. The discordance of closing and opening muscles during mastication might be caused by a basal ganglia lesion in this disease.

Intracellular processing and maturation of mutant gene products in hereditary beta-galactosidase deficiency (beta-galactosidosis).

Heterogeneous patterns of biosynthesis, posttranslational processing, and degradation were demonstrated for mutant enzymes in three clinical forms of beta-galactosidase deficiency (beta-galactosidosis): juvenile GM1-gangliosidosis, adult GM1-gangliosidosis, and Morquio B disease. The precursor of the mutant enzyme in adult GM1-gangliosidosis was not phosphorylated, and only a small portion of the gene product reached the lysosomes. The enzyme in Morquio B disease was normally processed and transported to lysosomes, but its catalytic activity was low. A common gene mutation in juvenile GM1-gangliosidosis (R201C) produced an enzyme protein that did not aggregate with protective protein in the lysosome, and was rapidly degraded by thiol proteases. This abnormal turnover was similar to that for the normal but dissociated beta-galactosidase in galactosialidosis. Protease inhibitors restored the enzyme activity in fibroblasts of this clinical form. A possible therapeutic approach is discussed for this specific type of enzyme deficiency.

Characterization of an Anti-β-galactosidase Antibody Recognizing a Precursor But Not a Mature Enzyme in Solution

A monospecific antibody was raised against a recombinant human 84-kDa β-galactosidase precursor protein, which had been produced with a baculovirus gene expression system and affinity-purified. It bound to the 64-kDa mature enzyme protein extracted from human fibroblasts and the antigenic recombinant precursor on immunoblotting, but neither the fibroblast-derived mature enzyme nor the 64-kDa mature protein-like tryptic product of the recombinant precursor protein was immunoprecipitated. We conclude that it specifically recognized the precursor but not the mature protein in solution. Immunoprecipitation with this anti-precursor antibody revealed that the precursor protein mainly accounted for the residual enzyme activity in fibroblasts from an adult GM1-gangliosidosis patient, and the mature protein accounted for the activity in fibroblasts from a juvenile GM1-gangliosidosis patient.

Accumulation of lysosphingolipids in tissues from patients with GM1 and GM2 gangliosidoses.

By using a sensitive method, we assayed lysocompounds of gangliosides and asialogangliosides in tissues from four patients with GM2 gangliosidosis (one with Sandhoff disease and three with Tay-Sachs disease) and from three patients with GM1 gangliosidosis [one with infantile type (fetus), one with late-infantile, and one with adult type]. In the brain and spinal cord of all the patients except for an adult GM1 gangliosidosis patient, abnormal accumulation of the lipids was observed, though the concentration in the fetal tissue was low. In GM2 gangliosidosis, the amounts of lyso GM2 ganglioside accumulated in the brain were similar among the patient with Sandhoff disease and the patients with Tay-Sachs disease, whereas the concentration of asialo lyso GM2 ganglioside in the brain was higher in the former patient than in the latter patients. By comparing the sphingoid bases of neutral sphingolipids, gangliosides, and lysosphingolipids, it was suggested that lysosphingolipids in the diseased tissue are synthesized by sequential glycosylation from free sphingoid bases, but not by deacylation of the sphingolipids. Because lysosphingolipids are known to be cytotoxic, the abnormally accumulated lysophingolipids may well be the pathogenetic agent for the neuronal degeneration in gangliosidoses.

Neuropathology of Late Onset Gangliosidoses

Neuropathological features of late onset gangliosidoses are reviewed. Although neuropathological studies are carried out on limited numbers of late onset cases, it appears that electron-dense heterogeneous conglomerates of neuronal inclusions increased with age admixed with more typical membranous cytoplasmic inclusions of gangliosidosis. Unlike early onset cases, which show extensive storage in cerebral cortical neurons, cortical neurons are involved less in late onset cases. In chronic (or adult) GM1 gangliosidosis, neuronal storage is almost exclusively limited to the basal ganglia, while in chronic (or adult) GM2 gangliosidosis storage neurons are more widely distributed in the thalamus, substantia nigra and other brainstem nuclei, and cerebellum is significantly affected.

Uptake and metabolism of radiolabelled GM1‐ganglioside in skin fibroblasts from controls and patients with GM1‐gangliosidosis

The uptake and metabolism of [3-3H-sphingosine]GM1-ganglioside was measured in cultured skin fibroblasts from controls and patients with infantile, juvenile and adult GM1-gangliosidosis. When dissolved in medium with phosphatidylserine, GM1-ganglioside was efficiently taken up by cultured skin fibroblasts and transferred into lysosomes. A linear increase in GM1-ganglioside endocytosis was shown with phosphatidylserine concentrations of up to 40 micrograms/ml. A pulse-chase study revealed that [3H]GM1-ganglioside was metabolized to GM2-ganglioside, GM3-ganglioside, ceramide dihexoside, ceramide monohexoside, ceramide and sphingosine. Sphingosine was recycled to sphingomyelin. In a 20-h pulse study, cell lines from patients with GM1-gangliosidosis of infantile, juvenile and adult types hydrolysed 2-5%, 20-44% and 54-58% of the total endocytosed GM1-ganglioside respectively. These values were lower than in control cells (64.17 +/- 5.43% (n = 10]. The hydrolysis rates of exogenous [3H]GM1-ganglioside in cultured fibroblasts from patients with various types of GM1-gangliosidosis closely reflected the clinical severity.

Ultrastructural findings of rectal and skin biopsies in adult GM1-gangliosidosis.

We report the ultrastructural findings in rectal and skin biopsies in four cases with adult GM1-gangliosidosis. The rectal specimens taken under endoscopic control contained submucosal plexuses, which were easily identified on light-microscopic and electron-microscopic examination. In all cases the ganglion cells in submucosal plexus contained characteristic osmiophilic lamellar inclusions, some of which were typical membranous cytoplasmic bodies, were commonly observed in the ganglion cells, Schwann's cells, vascular endothelial cells, and perithelial cells in rectal biopsy, and membrane-bound clear vacuoles were occasionally seen in the cytoplasm of rectal and cutaneous fibroblasts. However, the axons of unmyelinated nerves in both biopsies showed a normal appearance, and there was no significant change in the eccrine glands in skin biopsy. Comparing rectal and skin biopsies, the former was found to be more valuable for morphological diagnosis of this disease, and our ultrastructural examination of rectal biopsy revealed that enteric nerve cells were involved even in adult GM1-gangliosidosis with a benign course and restricted cerebral lesions.

Atypical adult GM1 gangliosidosis: biochemical comparison with other forms of primary beta-galactosidase deficiency.

We studied beta-galactosidase in skin fibroblasts from patients with different forms of beta-galactosidase deficiency: adult GM1 gangliosidosis, type 1 GM1 gangliosidosis, and Morquio B syndrome. Enzyme properties in the adult cases differed from the other disorders and also from normal controls. Genetic hybridization studies indicated that all three forms belong to the same complementation group. Therefore, the adult disorder must be due to a mutation of the structural gene for beta-galactosidase, which is allelic to the mutations in type 1 GM1 gangliosidosis and Morquio B syndrome.

Ganglioside GM1 metabolism in living human fibroblasts with beta-galactosidase deficiency.

The uptake and catabolism of [3H-ceramide]-GM1 was followed in living fibroblasts from patient with different forms of beta-galactosidase deficiency. Gangliosides are identified according to the nomenclature of Svennerholm (1963). A total inability to metabolize the ingested substrate was found in infantile GM1-gangliosidosis whereas cells from an adult GM1-gangliosidosis variant showed a slower rate of degradation, compared with controls. Morquio B fibroblasts had a comparable catabolism of GM1 as controls. Fibroblasts from different types of galactosialidosis, a recessive disease associated with a coexistent beta-galactosidase/neuraminidase deficiency all showed degradation of ingested GM1. In view of the molecular defect in this disease, this catabolism must be due to the 10-20% of monomeric beta-galactosidase molecules present in the lysosomes. Unexpectedly, in these cells an impaired metabolism of GM3 was found. The same finding was observed when cells with an isolated neuraminidase deficiency (mucolipidosis I) were loaded with GM1. A hypothesis is presented to explain these results.

Processing of human beta-galactosidase in GM1-gangliosidosis and Morquio B syndrome.

The nature of the molecular defect resulting in the beta-galactosidase deficiency in different forms of GM1-gangliosidosis and mucopolysaccharidosis IV B (Morquio B syndrome) was investigated. Normal and mutant cultured skin fibroblasts were labeled in vivo with [3H]leucine and immunoprecipitation studies with human anti-beta-galactosidase antiserum were performed, followed by polyacrylamide gel electrophoresis and fluorography. In Morquio B syndrome, the mutation does not interfere with the normal processing and intralysosomal aggregation of beta-galactosidase. In cells from infantile and adult GM1-gangliosidosis, 85-kDa precursor beta-galactosidase was found to be synthesized normally but more than 90% of the enzyme was subsequently degraded at one of the early steps in posttranslational processing. The residual 5-10% beta-galactosidase activity in adult GM1-gangliosidosis is 64-kDa mature lysosomal enzyme with normal catalytic properties but with a reduced ability of the monomeric form to aggregate into high molecular weight multimers. Knowledge of the exact nature of the molecular defect underlying beta-galactosidase deficiency in man may lead to a better understanding of the clinical and pathological heterogeneity among patients with different types of GM1-gangliosidosis and Morquio B syndrome.