Phenotype determining alleles in GM1 gangliosidosis patients bearing novel GLB1 mutations

Base editing of the GLB1 gene is therapeutic in GM1 gangliosidosis patient-derived cells

GM1 gangliosidosis is an autosomal recessive neurodegenerative lysosomal storage disease caused by pathogenic variants in the GLB1 gene, limiting the production of active lysosomal β-galactosidase. Phenotypic heterogeneity is due in part to variant type, location within GLB1, and the amount of residual enzyme activity; in the most severe form, death occurs in infancy. With no FDA approved therapeutics, development of efficacious strategies for the disease is pivotal. CRISPR/Cas based approaches have revolutionized precision medicine and have been indispensable to the development of treatments for several monogenic disorders with bespoke strategies central to current research pipelines. We used CRISPR/Cas-adenine base editing to correct the GLB1 c.380G>A (p.Cys127Tyr) variant in patient-derived dermal fibroblasts compound heterozygous with the GLB1 c.481T>G (p.Trp161Gly) pathogenic variant. Nucleofection of plasmids encoding the target sgRNA and ABEmax restored the canonical guanine (32.2 ± 2.2 % of the target allele) and synthesis of active β-galactosidase. Analysis of cellular markers of pathology revealed normalization of both primary glycoconjugate storage and lysosomal pathology. Furthermore, analysis of off-target sites nominated by the in silico tools Cas-OFFinder and/or CRISTA revealed no significant editing or indels. This study supports the use of CRISPR/Cas-based approaches for the treatment of GM1 gangliosidosis, and provides foundational data for future translational studies.

Case report: Preimplantation genetic testing for infantile GM1 gangliosidosis

Ganglioside-monosialic acid (GM1) gangliosidosis (ICD-10: E75.1; OMIM: 230500, 230600, 230650) is a rare autosomal recessive hereditary disease, lysosomal storage disorder caused by mutations in the GLB1 gene that lead to the absence or insufficiency of β-galactosidase. In this study, we report a case of a Russian family with a history of GM1 gangliosidosis. The family had a child who, from the age of 6 months, experienced a gradual loss of developmental skills, marked by muscle flaccidity, psychomotor retardation, hepatosplenomegaly, and the onset of tonic seizures by the age of 8 months. Funduscopic examination revealed a «cherry red spot» in the macula, which is crucial for the diagnosis of lipid storage disorders. To find the pathogenic variants responsible for these clinical symptoms, the next-generation sequencing approach was used. The analysis revealed two variants in the heterozygous state: a frameshift variant c.699delG (rs1452318343, ClinVar ID 928700) in exon 6 and a missense variant c.809A>C (rs371546950, ClinVar ID 198727) in exon 8 of the GLB1 gene. The spouses were advised to plan the pregnancy with assisted reproductive technology (ART), followed by preimplantation genetic testing for monogenic disorder (PGT-M) on the embryos. Trophectoderm biopsy was performed on 8 out of 10 resulting embryos at the blastocyst stage. To perform PGT-M, we developed a novel testing system, allowing for direct analysis of disease-causing mutations, as well as haplotype analysis based on the study of polymorphic markers-short tandem repeats (STR), located upstream and downstream of the GLB1 gene. The results showed that four embryos were heterozygous carriers of pathogenic variants in the GLB1 gene (#1, 2, 5, 8). Two embryos had a compound heterozygous genotype (#3, 4), while the embryos #7 and 9 did not carry disease-causing alleles of the GLB1 gene. The embryo #7 without pathogenic variants was transferred after consideration of its morphology and growth rate. Prenatal diagnosis in the first trimester showed the absence of the variants analyzed in the GLB1 gene in the fetus. The pregnancy resulted in the delivery of a female infant who did not inherit the disease-causing variants in the GLB1 gene.

Gene therapy approaches for GM1 gangliosidosis: Focus on animal and cellular studies

One of the most important inherited metabolic disorders is GM1 gangliosidosis, which is a progressive neurological disorder. The main cause of this disease is a genetic defect in the enzyme β-galactosidase due to a mutation in the glb1 gene. Lack of this enzyme in cells (especially neurons) leads to the accumulation of ganglioside substrate in nerve tissues, followed by three clinical forms of GM1 disease (neonatal, juvenile, and adult variants). Genetically, many mutations occur in the exons of the glb1 gene, such as exons 2, 6, 15, and 16, so the most common ones reported in scientific studies include missense/nonsense mutations. Therefore, many studies have examined the genotype-phenotype relationships of this disease and subsequently using gene therapy techniques have been able to reduce the complications of the disease and alleviate the signs and symptoms of the disease. In this regard, the present article reviews the general features of GM1 gangliosidosis and its mutations, as well as gene therapy studies and animal and human models of the disease.

Are GMI gangliosidosis and Morquio type B two different disorders or part of one phenotypic spectrum?

Monosialotetrahexosylganglioside (GMI) gangliosidosis and Morquio type B (MorB) are two lysosomal storage disorders (LSDs) caused by the same enzyme deficiency, β-galactosidase (βgal). GMI gangliosidosis, associated with GMI ganglioside accumulation, is a neurodegenerative condition characterized by psychomotor regression, visceromegaly, cherry red spot, and facial and skeletal abnormalities. MorB is characterized by prominent and severe skeletal deformities due to keratan sulfate (KS) accumulation. There are only a few reports on intermediate phenotypes between GMI gangliosidosis and MorB. The presentation of two new patients with this rare intermediate phenotype motivated us to review the literature, to study differences and similarities between GMI gangliosidosis and MorB, and to speculate about the possible mechanisms that may contribute to the differences in clinical presentation. In conclusion, we hypothesize that GMI gangliosidosis and MorB are part of one phenotypic spectrum of the same disease and that the classification of LSDs might need to be revised.

GM1 Gangliosidosis: Mechanisms and Management

The lysosomal storage disorder, GM1 gangliosidosis (GM1), is a neurodegenerative condition resulting from deficiency of the enzyme β-galactosidase (β-gal). Mutation of the GLB1 gene, which codes for β-gal, prevents cleavage of the terminal β-1,4-linked galactose residue from GM1 ganglioside. Subsequent accumulation of GM1 ganglioside and other substrates in the lysosome impairs cell physiology and precipitates dysfunction of the nervous system. Beyond palliative and supportive care, no FDA-approved treatments exist for GM1 patients. Researchers are critically evaluating the efficacy of substrate reduction therapy, pharmacological chaperones, enzyme replacement therapy, stem cell transplantation, and gene therapy for GM1. A Phase I/II clinical trial for GM1 children is ongoing to evaluate the safety and efficacy of adeno-associated virus-mediated GLB1 delivery by intravenous injection, providing patients and families with hope for the future.

Rapid Identification of New Biomarkers for the Classification of GM1 Type 2 Gangliosidosis Using an Unbiased 1H NMR-Linked Metabolomics Strategy

Biomarkers currently available for the diagnosis, prognosis, and therapeutic monitoring of GM1 gangliosidosis type 2 (GM1T2) disease are mainly limited to those discovered in targeted proteomic-based studies. In order to identify and establish new, predominantly low-molecular-mass biomarkers for this disorder, we employed an untargeted, multi-analyte approach involving high-resolution 1H NMR analysis coupled to a range of multivariate analysis and computational intelligence technique (CIT) strategies to explore biomolecular distinctions between blood plasma samples collected from GM1T2 and healthy control (HC) participants (n = 10 and 28, respectively). The relationship of these differences to metabolic mechanisms underlying the pathogenesis of GM1T2 disorder was also investigated. 1H NMR-linked metabolomics analyses revealed significant GM1T2-mediated dysregulations in ≥13 blood plasma metabolites (corrected p < 0.04), and these included significant upregulations in 7 amino acids, and downregulations in lipoprotein-associated triacylglycerols and alanine. Indeed, results acquired demonstrated a profound distinctiveness between the GM1T2 and HC profiles. Additionally, employment of a genome-scale network model of human metabolism provided evidence that perturbations to propanoate, ethanol, amino-sugar, aspartate, seleno-amino acid, glutathione and alanine metabolism, fatty acid biosynthesis, and most especially branched-chain amino acid degradation (p = 10-12-10-5) were the most important topologically-highlighted dysregulated pathways contributing towards GM1T2 disease pathology. Quantitative metabolite set enrichment analysis revealed that pathological locations associated with these dysfunctions were in the order fibroblasts > Golgi apparatus > mitochondria > spleen ≈ skeletal muscle ≈ muscle in general. In conclusion, results acquired demonstrated marked metabolic imbalances and alterations to energy demand, which are consistent with GM1T2 disease pathogenesis mechanisms.

Morquio B Disease. Disease Characteristics and Treatment Options of a Distinct GLB1-Related Dysostosis Multiplex

Morquio B disease (MBD) is an autosomal recessive GLB1-gene-related lysosomal storage disease, presenting with a peculiar type of dysostosis multiplex which is also observed in GALNS-related Morquio A disease. MBD may present as pure skeletal phenotype (pure MBD) or in combination with the neuronopathic manifestations seen in type 2 (juvenile) or type 3 (late onset) GM1 gangliosidosis (MBD plus). The main skeletal features are progressive growth impairment, kyphoscoliosis, coxa/genua valga, joint laxity, platyspondyly and odontoid hypoplasia. The main neuronopathic features are dystonia, ataxia, and intellectual/developmental/speech delay. Spinal cord compression occurs as a complication of spinal dysostosis. Chronic pain is reported, along with mobility issues and challenges with daily living and self-care activities, as the most common health concern. The most commonly reported orthopedic surgeries are hip and knee replacements. Keratan sulphate-derived oligosaccharides are characteristic biomarkers. Residual β-galactosidase activities measured against synthetic substrates do not correlate with the phenotype. W273 L and T500A are the most frequently observed GLB1 variants in MBD, W273L being invariably associated with pure MBD. Cytokines play a role in joint destruction and pain, providing a promising treatment target. In the future, patients may benefit from small molecule therapies, and gene and enzyme replacement therapies, which are currently being developed for GM1 gangliosidosis.

Clinical and genetic characteristics and prenatal diagnosis of patients presented GDD/ID with rare monogenic causes

Background

Global developmental delay/intellectual disability (GDD/ID), used to be named as mental retardation (MR), is one of the most common phenotypes in neurogenetic diseases. In this study, we described the diagnostic courses, clinical and genetic characteristics and prenatal diagnosis of a cohort with patients presented GDD/ID with monogenic causes, from the perspective of a tertiary genetic counseling and prenatal diagnostic center.

Method

We retrospectively analyzed the diagnostic courses, clinical characteristics, and genetic spectrum of patients presented GDD/ID with rare monogenic causes. We also conducted a follow-up study on prenatal diagnosis in these families. Pathogenicity of variants was interpreted by molecular geneticists and clinicians according to the guidelines of the American College of Medical Genetics and Genomics (ACMG).

Results

Among 81 patients with GDD/ID caused by rare monogenic variants it often took 0.5–4.5 years and 2–8 referrals to obtain genetic diagnoses. Devlopmental delay typically occurred before 3 years of age, and patients usually presented severe to profound GDD/ID. The most common co-existing conditions were epilepsy (58%), microcephaly (21%) and facial anomalies (17%). In total, 111 pathogenic variants were found in 62 different genes among the 81 pedigrees, and 56 variants were novel. The most common inheritance patterns in this outbred Chinese population were autosomal dominant (AD; 47%), following autosomal recessive (AR; 37%), and X-linked (XL; 16%). SCN2A, SHANK3 and STXBP1 were important causal genes. Hot-spot variants were rarely found. By the follow-up, 33 affected families, including 15, 13 and 5 families inherited in AR, AD and XL modes respectively, had undergone prenatal diagnosis. And the recurrence rates are 26.7%, 15.4% and 20% for families inherited in AR, AD, and XL patterns.

Conclusion

Patients presented with GDD/ID caused by rare single gene variants are characterized by early onset, relatively severe symptoms and great clinical variability and genetic heterogeneity. Timely referrals to genetic counseling and prenatal diagnostic laboratories are important for affected families planning to have additional children.

The natural history of Type 1 infantile GM1 gangliosidosis: A literature-based meta-analysis

INTRODUCTION

Type 1 GM1 gangliosidosis is an ultra-rare, rapidly fatal lysosomal storage disorder, with life expectancy of <3 years of age. To date, only one prospective natural history study of limited size has been reported. Thus, there is a need for additional research to provide a better understanding of the progression of this disease. We have leveraged the past two decades of medical literature to conduct the first comprehensive retrospective study characterizing the natural history of Type 1 GM1 gangliosidosis.

OBJECTIVES

The objectives of this study were to establish a large sample of patients from the literature in order to identify: 1) clinically distinguishing factors between Type 1 and Type 2 GM1 gangliosidosis, 2) age at first symptom onset, first hospital admission, diagnosis, and death, 3) time to onset of common clinical findings, and 4) timing of developmental milestone loss.

METHODS

PubMed was searched with the keyword "GM1 Gangliosidosis" and for articles from the year 2000 onwards. A preliminary review of these results was conducted to establish subtype classification criteria for inclusion of only Type 1 patients, resulting in 44 articles being selected to generate the literature dataset of 154 Type 1 GM1 gangliosidosis patients. Key clinical events of these patient cases were recorded from the articles.

RESULTS

Comprehensive subtyping criteria for Type 1 GM1 gangliosidosis were created, and clinical events, including onset, diagnosis, death, and symptomology, were mapped over time. In this dataset, average age of diagnosis was 8.7 months, and average age of death was 18.9 months.

DISCUSSION

This analysis demonstrates the predictable clinical course of this disease, as almost all patients experienced significant multi-organ system dysfunction and neurodevelopmental regression, particularly in the 6- to 18-month age range. Patients were diagnosed at a late age relative to disease progression, indicating the need for improved public awareness and screening.

CONCLUSION

This study highlights the significant burden of illness in this disease and provides critical natural history data to drive earlier diagnosis, inform clinical trial design, and facilitate family counseling.

The Clinical and Molecular Spectrum of GM1 Gangliosidosis

OBJECTIVE

To evaluate the clinical presentation of patients with GM1 gangliosidosis and to determine whether specific clinical or biochemical signs could lead to a prompt diagnosis.

STUDY DESIGN

We retrospectively analyzed clinical, biochemical, and genetic data of 22 patients with GM1 gangliosidosis from 5 metabolic centers in Germany and Austria.

RESULTS

Eight patients were classified as infantile, 11 as late-infantile, and 3 as juvenile form. Delay of diagnosis was 6 ± 2.6 months in the infantile, 2.6 ± 3.79 years in the late-infantile, and 14 ± 3.48 years in the juvenile form. Coarse facial features, cherry red spots, and visceromegaly occurred only in patients with the infantile form. Patients with the late-infantile and juvenile forms presented with variable neurologic symptoms. Seventeen patients presented with dystonia and 14 with dysphagia. Laboratory analysis revealed an increased ASAT concentration (13/20), chitotriosidase activity (12/15), and pathologic urinary oligosaccharides (10/19). Genotype analyses revealed 23 causative or likely causative mutations in 19 patients, 7 of them being novel variants. In the majority, a clear genotype-phenotype correlation was found.

CONCLUSIONS

Diagnosis of GM1 gangliosidosis often is delayed, especially in patients with milder forms of the disease. GM1 gangliosidosis should be considered in patients with progressive neurodegeneration and spastic-dystonic movement disorders, even in the absence of visceral symptoms or cherry red spots. ASAT serum concentrations and chitotriosidase activity may be of value in screening for GM1 gangliosidosis.

Morquio-B disease: Clinical and genetic characteristics of a distinct GLB1-related dysostosis multiplex

Background

Morquio-B disease (MBD) is a distinct GLB1-related dysostosis multiplex involving the trabecular parts of long bones and spine, presenting a mild phenocopy of GALNS-related Morquio-A disease.

Methods

We analyzed 63 (n = 62 published) cases with MBD to describe their clinical, biochemical and genetic features.

Results

Forty-one of 51 cases with informative clinical data had pure MBD including progressive growth impairment, kyphoscoliosis, coxa/genua valga, joint laxity, platyspondyly, odontoid hypoplasia. Ten of 51 had MBD plus neuronopathic manifestations including intellectual/developmental/speech delay, spasticity, ataxia dystonia. Corneal clouding, cardiac valve pathology, hepatosplenomegaly, spinal cord compression were infrequent and atlantooccipital dislocation, cardiomyopathy and cherry red spot were never reported. Urinary glycosaminoglycan and oligosaccharide excretion was consistently abnormal. Keratan sulphate-derived oligosaccharides were only detected using LC-MS/MS-based methods. Residual β-galactosidase activities measured against synthetic substrates were 0%-17%.Among 28 GLB1 variants, W273 L (34/94 alleles) and T500A (11/94 alleles) occurred most frequently. W273L was invariably associated with pure MBD. Pure MBD also was reported in a case homozygous for R201H, and in the majority of cases carrying the T500A variant. Homozygous Y333C and G438E were associated with MBD plus neuronopathic manifestations. T82M, R201H, and H281Y, observed in seven alleles, previously have been found sensitive to experimental chaperones.

Conclusion

Data provide a basis for future systematic collection of clinical, biochemical, morphologic, and genetic data of this ultra-rare condition.

Genotype-phenotype correlation of gangliosidosis mutations using in silico tools and homology modeling

Gangliosidoses, including GM1-gangliosidosis and GM2-gangliosidosis (Tay-Sachs disease and Sandhoff disease), are lysosomal disorders resulting from enzyme deficiencies and accumulation of gangliosides. Phenotypes of gangliosidoses range from infantile, late-infantile, juvenile, and to the adult form. The genotype-phenotype correlation is essential for prognosis and clinical care planning for patients with a gangliosidosis condition. Previously, we have developed a method to establish the genotype-phenotype correlation of another lysosomal disease, mucopolysaccharidosis type I, with in silico tools. This same method was applied to analyze the genotype and phenotype of 38 patients diagnosed with a gangliosidosis disease in the United States. Out of 40 mutations identified, 3 were novel, including p.Tyr192His and p.Phe556Ser of the GLB1 gene and p.Gly461Val of the HEXA gene. Furthermore, the mutant protein structure of all missense mutations was constructed by homology modeling. A systemic structural analysis of these models revealed the specific mechanisms of how each mutation may lead to the disease. In summary, the method developed in this study holds promise as a tool that can be broadly applicable to other lysosomal diseases and monogenic diseases.

Clinical and molecular characteristics of 11 Chinese probands with GM1 gangliosidosis

GM1 gangliosidosis is an autosomal recessive lysosomal storage disease caused by the deficiency of β-galactosidase activity, precisely due to mutations in the GLB1 gene. To explore the clinical and molecular characteristics of GM1 gangliosidosis patients from China, GLB1 gene were analyzed in 11 probands with GM1 gangliosidosis by exploiting direct Sanger-sequencing. Among them, five patients were classified as the infantile type and the remaining six as the late-infantile or juvenile type. In these probands, eight novel mutations p.Y50N, p.Y237C, p.S267F, p.G453R, p.K578 N, c.618delC, c.475_478delGACA and c.1979_1980insG have been identified. Among them, three novel missense mutations p.Y50N, p.S267F and p.G453R were transiently transfected in COS-7 cells by plasmid system for functional verification. In vitro GLB1 activities carrying the aforesaid missense mutants p.Y50N, p.S267F and p.G453R were 0.11%, 0 and 0.55% of wild-type, respectively. Mutation c.495_497delTCT and p.S149F accounted for 22.7 and 13.6% of the mutant alleles, respectively. Our results expand the spectrum of GLB1 gene, provide new insights into the clinical and molecular characteristics of GM1 gangliosidosis in China.

Morquio B patient/caregiver survey: First insight into the natural course of a rare GLB1 related condition

Morquio B disease (MBD) or Mucopolysaccharidosis type IV B (MPS IV B) is caused by particular GLB1 mutations specifically affecting the affinity of beta-galactosidase to keratan sulphate, resulting in dysostosis multiplex resembling Morquio A (MPS IV A) disease (GALNS deficiency). Additional neuronopathic features of GM1 II/III (juvenile/adult) gangliosidosis have been reported in some patients. Our patient/caregiver online survey was aimed at elucidating the clinical manifestations of this ultra-rare condition. Comparing to previously published data on MPS IV A, the 30 respondents in our MBD group presented with greater growth chart values (weight and height) and with lesser effects of odontoid hypoplasia. The most common concerns are: (1) mobility issues - 84% having difficulty walking; (2) chronic pain - 96%; (3) surgeries - average 3 per person, 80% for hip problems; (4) hip dysplasia, knee/ankle concerns, and scoliosis. Approximately 50% of MBD participants live independently and actively contributing to society. Evidence from our survey results supports the notion that skeletal manifestations in MBD are milder than in the majority of patients with MPS IV A. The data collected will help with the establishment of clinically meaningful outcomes for future therapeutic trials, and with the counseling of newly diagnosed patients about their health expectations.

Diagnostic challenge for the rare lysosomal storage disease: Late infantile GM1 gangliosidosis

BACKGROUND

GM1 gangliosidosis is a rare lysosomal storage disorder caused by GLB1 mutations. Because of its extreme rarity and symptoms that overlap with other neurodegenerative diseases, its diagnosis is sometimes challenging, especially in the late infantile form with less severe phenotype. We aim to expand the clinical and genetic spectrum of late infantile GM1 gangliosidosis.

METHODS

We confirmed a diagnosis of GM1 gangliosidosis based on GLB1 mutations and/or the deficiency of β-galactosidase activity. We identified the first two cases by whole-exome sequencing, and then the other six cases by direct sequencing of GLB1 with enzyme analysis.

RESULTS

All eight patients presented with developmental delay or regression during late infancy and later developed epilepsy, mostly intractable generalized tonic seizures. No clinical signs of storage disorders were noted except for skeletal abnormalities. Interestingly, we found aspartate transaminase (AST) elevations alone with normal alanine transaminase (ALT) levels in all patients. The recurrent mutation, p.D448V in GLB1, accounted for 50.0% of total alleles in our cohort.

CONCLUSIONS

With a high index of clinical suspicion, skeletal survey and AST level would be important for early diagnosis of GM1 gangliosidosis. In addition, we would highlight the clinical usefulness of whole-exome sequencing in the diagnosis of non-classical presentation of ultra-rare neurodegenerative disease in children.

Recurrent and novel GLB1 mutations in India

GM1 gangliosidosis is a lysosomal storage disorder caused by mutations in the GLB1 gene, leading to the deficiency of the enzyme β-d-galactosidase. In this study, we report molecular findings in 50 Asian Indian families with GM1 gangliosidosis. We sequenced all the exons and flanking intronic sequences of GLB1 gene. We identified 33 different mutations (20 novel and 13 previously reported). The novel mutations include 12 missense (p.M1?, p.E129Q, p.G134R, p.L236P, p.G262E, p.L297F, p.Y331C, p.G414V, p.K493N, p.L514P, p.P597L, p.T600I), four splicing (c.246-2A>G, c.397-2A>G, c.552+1G>T, c.956-2A>G), three indels (p.R22Qfs*8, p.L24Cfs*47, p.I489Qfs*4) and one nonsense mutation (p.Q452*). Most common mutations identified in this study were c.75+2InsT (14%) and p.L337P (10%). Known mutations accounted for 67% of allele frequency in our cohort of patients, suggesting that these mutations in GLB1 are recurrent across different populations. Twenty three mutations were localized in the TIM barrel domain, β-domain 1 and β-domain 2. In silico sequence and structure analysis of GLB1 reveal that all the novel mutations affect the function and structure of the protein. We hereby report on the largest series of patients with GM1 gangliosidosis and the first from India.

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.

Biochemical and molecular characterization of novel mutations in GLB1 and NEU1 in patient cells with lysosomal storage disorders

Lysosomes are cytoplasmic compartments that contain many acid hydrolases and play critical roles in the metabolism of a wide range of macromolecules. Deficiencies in lysosomal enzyme activities cause genetic diseases, called lysosomal storage disorders (LSDs). Many mutations have been identified in the genes responsible for LSDs, and the identification of mutations is required for the accurate molecular diagnoses. Here, we analyzed cell lines that were derived from two different LSDs, GM1 gangliosidosis and sialidosis. GM1 gangliosidosis is caused by mutations in the GLB1 gene that encodes β-galactosidase. A lack of β-galactosidase activity leads to the massive accumulation of GM1 ganglioside, which results in neurodegenerative pathology. Mutations in the NEU1 gene that encodes lysosomal sialidase cause sialidosis. Insufficient activity of lysosomal sialidase progressively increases the accumulation of sialylated molecules, and various clinical symptoms, including mental retardation, appear. We sequenced the entire coding regions of GLB1 and NEU1 in GM1 gangliosidosis and sialidosis patient cells, respectively. We found the novel mutations p.E186A in GLB1 and p.R347Q in NEU1, as well as many other mutations that have been previously reported. We also demonstrated that patient cells containing the novel mutations showed the molecular phenotypes of the corresponding disease. Further structural analysis suggested that these novel mutation sites are highly conserved and important for enzyme activity.

Therapeutic chaperone effect of N-octyl 4-epi-β-valienamine on murine G(M1)-gangliosidosis

Therapeutic chaperone effect of a valienamine derivative N-octyl 4-epi-β-valienamine (NOEV) was studied in G(M1)-gangliosidosis model mice. Phamacokinetic analysis revealed rapid intestinal absorption and renal excretion after oral administration. Intracellular accumulation was not observed after continuous treatment. NOEV was delivered to the central nervous system through the blood-brain barrier to induce high expression of the apparently deficient β-galactosidase activity. NOEV treatment starting at the early stage of disease resulted in remarkable arrest of neurological progression within a few months. Survival time was significantly prolonged. This result suggests that NOEV chaperone therapy will be clinically effective for prevention of neuronal damage if started early in life hopefully also in human patients with G(M1)-gangliosidosis.

Fluorous iminoalditols act as effective pharmacological chaperones against gene products from GLB₁ alleles causing GM1-gangliosidosis and Morquio B disease

Unlike replacement therapy by infusion of exogenous recombinant lysosomal enzymes, pharmacological chaperones aim at a gain of function of endogenous gene products. Deficits resulting from missense mutations may become treatable by small, competitive inhibitors binding to the catalytical site and thus correcting the erroneous conformation of mutant enzymes. This may prevent their premature degradation and normalize intracellular trafficking as well as biological half-life. A major limitation currently arises from the huge number of individual missense mutations and the lack of knowledge on the structural requirements for specific interaction with mutant protein domains. Our previous work on mutations of the β-galactosidase (β-gal) gene, causing GM1 gangliosidosis (GM1) and Morquio B disease (MBD), respectively, characterized clinical phenotypes as well as biosynthesis, intracellular transport and subcellular localization of mutants. We recently identified an effective chaperone, DL-HexDGJ (Methyl 6-{[N(2)-(dansyl)-N(6)-(1,5-dideoxy-D-galactitol-1,5-diyl)- L-lysyl]amino} hexanoate), among a series of N-modified 1-deoxygalactonojirimycin derivatives carrying a dansyl group in its N-acyl moiety. Using novel and flexible synthetic routes, we now report on the effects of two oligofluoroalkyl-derivatives of 1-deoxygalactonojirimycin, Ph(TFM)(2)OHex-DGJ (N-(α,α-di-trifluoromethyl) benzyloxyhexyl-1,5-dideoxy-1,5-imino-D: -galactitol) and (TFM)(3)OHex-DGJ (N-(Nonafluoro-tert-butyloxy)hexyl-1,5-dideoxy-1,5-imino-D: -galactitol) on the β-gal activity of GM1 and MBD fibroblasts. Both compounds are competitive inhibitors and increase the residual enzyme activities up to tenfold over base line activity in GM1 fibroblasts with chaperone-sensitive mutations. Western blots showed that this was due to a normalization of protein transport and intralysosomal maturation. The fact that the novel compounds were effective at very low concentrations (0.5-10 μM) in the cell culture medium as well as their novel chemical character suggest future testing in animal models. This may contribute to new aspects for efficient and personalized small molecule treatment of lysosomal storage diseases.

β-Galactosidosis in Patient with Intermediate GM1 and MBD Phenotype

A 5-year-old girl with clinical and biochemical phenotypes encompassing both GM1-gangliosidosis (GM1) and Morquio B disease (MBD) is described. Mild generalized skeletal dysplasia and keratan sulfaturia were consistent with a diagnosis of MBD, while developmental delay and GM1-specific oligosacchariduria were consistent with GM1 gangliosidosis. No observable β-galactosidase activity was detected in leukocytes, and two mutations, p.R201H (c.602G>A) and p.G311R (c.931G>A), were identified by gene sequencing. The R201H substitution has been previously reported in patients with both GM1 and MBD, and G311R is a novel mutation. Our patient represents a further example of the clinical heterogeneity that can result from mutations at the β-galactosidase locus.

Four novel mutations in the β-galactosidase gene identified in infantile type of GM1 gangliosidosis

OBJECTIVES

The aim of this study is to find out mutations of Turkish GM1 gangliosidosis patients and to make genotype-phenotype correlations.

DESIGN AND METHODS

β-galactosidase activities were measured by using fluorometric substrate. Mutation screening of 16 exons of β-galactosidase gene and mutation detection were done by PCR-SSCP and DNA sequencing, respectively.

RESULTS

Four new mutations, c.188_189insT in exon 2, c.569_570insA in exon 6, p.K142Q in exon 4, p.G190D in exon 6, and one known mutation p.P549L in exon 15, were identified in the β-galactosidase gene in 5 Turkish patients. Mutations in exons 4 and 6 are in the active site and mutation in exon is in the galactose-binding domain of the β-galactosidase gene.

CONCLUSION

This is the first mutational analysis performed in Turkish GM1 gangliosidosis patients and shows the molecular heterogeneity of the disease in Turkish population. All identified mutations result in severe enzyme deficiency and infantile phenotype.

GM1 gangliosidosis and Morquio B disease: an update on genetic alterations and clinical findings

GM1 gangliosidosis and Morquio B syndrome, both arising from beta-galactosidase (GLB1) deficiency, are very rare lysosomal storage diseases with an incidence of about 1:100,000-1:200,000 live births worldwide. Here we report the beta-galactosidase gene (GLB1) mutation analysis of 21 unrelated GM1 gangliosidosis patients, and of 4 Morquio B patients, of whom two are brothers. Clinical features of the patients were collected and compared with those in literature. In silico analyses were performed by standard alignments tools and by an improved version of GLB1 three-dimensional models. The analysed cohort includes remarkable cases. One patient with GM1 gangliosidosis had a triple X syndrome. One patient with juvenile GM1 gangliosidosis was homozygous for a mutation previously identified in Morquio type B. A patient with infantile GM1 gangliosidosis carried a complex GLB1 allele harbouring two genetic variants leading to p.R68W and p.R109W amino acid changes, in trans with the known p.R148C mutation. Molecular analysis showed 27 mutations, 9 of which are new: 5 missense, 3 microdeletions and a nonsense mutation. We also identified four new genetic variants with a predicted polymorphic nature that was further investigated by in silico analyses. Three-dimensional structural analysis of GLB1 homology models including the new missense mutations and the p.R68W and p.R109W amino acid changes showed that all the amino acid replacements affected the resulting protein structures in different ways, from changes in polarity to folding alterations. Genetic and clinical associations led us to undertake a critical review of the classifications of late-onset GM1 gangliosidosis and Morquio B disease.

Three novel beta-galactosidase gene mutations in Han Chinese patients with GM1 gangliosidosis are correlated with disease severity

BACKGROUND

GM1 gangliosidosis (GM1) is an autosomal recessive lysosomal storage disease caused by deficiency of acid beta-galactosidase (GLB1; EC3.2.1.23). Here, we identify three novel mutations in the GLB1 gene from two Han Chinese patients with GM1 that appear correlated with clinical phenotype.

METHODS

One of the two Han Chinese patients with GM1 presented with the juvenile form, and the other with the infantile form with cardiac involvement. Sequencing of the entire GLB1 gene revealed three novel mutations (p.H102 D, p.G494V, c.495_497delTCT), which were absent in 94 normal controls. Transient expression of cDNA encoding these variants was performed in COS-1 cells to evaluate β-galactosidase activities.

RESULTS

The first case (patient 1) with the juvenile form contained two missense mutations, p.H102 D and p.A301V. Patient 2 diagnosed with the infantile form of the disease with cardiac involvement was compound heterozygous for p.G494V and c.495_497delTCT mutations. All mutant beta-galactosidases exhibited significantly reduced activity (12%, 0%, 0%, and 0% for p.H102 D, p.A301V, p.G494V, and c.495_497delTCT), compared with the wild-type beta-galactosidase cDNA clone. The mutations identified in patient 2 with cardiomyopathy were localized in the GLB1 gene region common to both lysosomal beta-galactosidase and elastin binding protein (EBP), and caused a deletion in the elastin-binding domain of EBP.

CONCLUSIONS

All four mutations identified in Han Chinese patients induce significant suppression of β-galactosidase activity, correlating with severity of disease and presence of cardiomyopathy.