Morquio B disease: From pathophysiology towards diagnosis

Morquio B disease is an attenuated phenotype within the spectrum of beta galactosidase (GLB1) deficiencies. It is characterised by dysostosis multiplex, ligament laxity, mildly coarse facies and heart valve defects due to keratan sulphate accumulation, predominantly in the cartilage. Morquio B patients have normal neurological development, setting them apart from those with the more severe GM1 gangliosidosis. Morquio B disease, with an incidence of 1:250.000 to 1:1.000.000 live births, is very rare. Here we report the clinical-biochemical data of nine patients. High amounts of keratan sulfate were detected using LC-MS/MS in the patients' urinary samples, while electrophoresis, the standard procedure of qualitative glycosaminoglycans analysis, failed to identify this metabolite in any of the patients' samples. We performed molecular analyses at gene, gene expression and protein expression levels, for both isoforms of the GLB1 gene, lysosomal GLB1, and the cell-surface expressed Elastin Binding Protein. We characterised three novel GLB1 mutations [c.75 + 2 T > G, c.575A > G (p.Tyr192Cys) and c.2030 T > G (p.Val677Gly)] identified in three heterozygous patients. We also set up a copy number variation assay by quantitative PCR to evaluate the presence of deletions/ insertions in the GLB1 gene. We propose a diagnostic plan, setting out the specific clinical- biochemical and molecular features of Morquio B, in order to avoid misdiagnoses and improve patients' management.

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.

Infantile gangliosidoses: Mapping a timeline of clinical changes

BACKGROUND

Infantile gangliosidoses include GM1 gangliosidosis and GM2 gangliosidosis (Tay-Sachs disease, Sandhoff disease). To date, natural history studies in infantile GM2 (iGM2) have been retrospective and conducted through surveys. Compared to iGM2, there is even less natural history information available on infantile GM1 disease (iGM1). There are no approved treatments for infantile gangliosidoses. Substrate reduction therapy using miglustat has been tried, but is limited by gastrointestinal side effects. Development of effective treatments will require identification of meaningful outcomes in the setting of rapidly progressive and fatal diseases.

OBJECTIVES

This study aimed to establish a timeline of clinical changes occurring in infantile gangliosidoses, prospectively, to: 1) characterize the natural history of these diseases; 2) improve planning of clinical care; and 3) identify meaningful future treatment outcome measures.

METHODS

Patients were evaluated prospectively through ongoing clinical care.

RESULTS

Twenty-three patients were evaluated: 8 infantile GM1, 9 infantile Tay-Sachs disease, 6 infantile Sandhoff disease. Common patterns of clinical change included: hypotonia before 6months of age; severe motor skill impairment within first year of life; seizures; dysphagia and feeding-tube placement before 18months of age. Neurodevelopmental testing scores reached the floor of the testing scale by 20 to 28months of age. Vertebral beaking, kyphosis, and scoliosis were unique to patients with infantile GM1. Chest physiotherapy was associated with increased survival in iGM1 (p=0.0056). Miglustat combined with a low-carbohydrate ketogenic diet (the Syner-G regimen) in patients who received a feeding-tube was associated with increased survival in infantile GM1 (p=0.025).

CONCLUSIONS

This is the first prospective study of the natural history of infantile gangliosidoses and the very first natural history of infantile GM1. The homogeneity of the infantile gangliosidoses phenotype as demonstrated by the clinical events timeline in this study provides promising secondary outcome measure candidates. This study indicates that overall survival is a meaningful primary outcome measure for future clinical trials due to reliable timing and early occurrence of this event. Combination therapy approaches, instead of monotherapy approaches, will likely be the best way to optimize clinical outcomes. Combination therapy approaches include palliative therapies (e.g., chest physiotherapy) along with treatments that address the underlying disease pathology (e.g. miglustat or future gene therapies).

The GM1 and GM2 Gangliosidoses: Natural History and Progress toward Therapy

The gangliosidoses are lysosomal storage disorders caused by accumulation of GM1 or GM2 gangliosides. GM1 gangliosidosis has both central nervous system and systemic findings; while, GM2 gangliosidosis is restricted primarily to the central nervous system. Both disorders have autosomal recessive modes of inheritance and a continuum of clinical presentations from a severe infantile form to a milder, chronic adult form. Both are devastating diseases without cure or specific treatment however, with the use of supportive aggressive medical management, the lifespan and quality of life has been extended for both diseases. Naturally occurring and engineered animal models that mimic the human diseases have enhanced our understanding of the pathogenesis of disease progression. Some models have shown significant improvement in symptoms and lifespan with enzyme replacement, substrate reduction, and anti-inflammatory treatments alone or in combination. More recently gene therapy has shown impressive results in large and small animal models. Treatment with FDA-approved glucose analogs to reduce the amount of ganglioside substrate is used as off-label treatments for some patients. Therapies also under clinical development include small molecule chaperones and gene therapy.

1-Deoxy-D-galactonojirimycins with dansyl capped N-substituents as β-galactosidase inhibitors and potential probes for GM1 gangliosidosis affected cell lines

Two simple and reliably accessible intermediates, N-carboxypentyl- and N-aminohexyl-1-deoxy-D-galactonojirimycin were employed for the synthesis of a set of terminally N-dansyl substituted derivatives. Reaction of the terminal carboxylic acid of N-carboxypentyl-1-deoxy-D-galactonojirimycin with N-dansyl-1,6-diaminohexane provided the chain-extended fluorescent derivative. Employing bis(6-dansylaminohexyl)amine, the corresponding branched di-N-dansyl compound was obtained. Partially protected N-aminohexyl-1-deoxy-D-galactonojirimycin served as intermediate for two additional chain-extended fluorescent 1-deoxy-D-galactonojirimycin (1-DGJ) derivatives featuring terminal dansyl groups in the N-alkyl substituent. These new compounds are strong inhibitors of d-galactosidases and may serve as leads en route to pharmacological chaperones for GM1-gangliosidosis.

Beneficial effects of substrate reduction therapy in a mouse model of GM1 gangliosidosis

GM1 gangliosidosis is an inherited neurodegenerative disorder caused by lysosomal beta-galactosidase deficiency, resulting in the storage of GM1 and GA1, primarily in the central nervous system. This disease typically afflicts infants and young children and there is currently no effective therapy. Substrate reduction therapy (SRT) could be of potential benefit. The imino sugars N-butyldeoxynojirimycin (NB-DNJ, miglustat, Zavesca) and N-butyldeoxygalactonojirimycin (NB-DGJ) used for SRT inhibit glucosylceramide synthase (GlcCerS) that catalyses the first committed step in glycosphingolipid biosynthesis. We have compared the efficacy and tolerability of NB-DNJ and NB-DGJ in the beta-galactosidase knockout mouse. NB-DGJ was better tolerated than NB-DNJ, due to intrinsic gastrointestinal tract dysfunction that was exacerbated by NB-DNJ. However, functional improvement was greatest with NB-DNJ treatment which may potentially be caused by novel anti-inflammatory properties of NB-DNJ.

Motor and reflex testing in GM1-gangliosidosis model mice

A large number of genetic disease model mice have been produced by genetic engineering. However, phenotypic analysis is not sufficient, particularly for brain dysfunction in neurogenetic diseases. We tried to develop a new assessment system mainly for motor and reflex functions in G(M1)-gangliosidosis model mice. Two genetically engineered model mouse strains were used for this study: the beta-galactosidase-deficient knockout mouse representing infantile G(M1)-gangliosidosis (severe form), and transgenic mouse representing juvenile G(M1)-gangliosidosis (mild form). We modified human child neurology techniques, and selected eleven tests for motor assessment and reflex testing. The test results were scored in four grades: 0 (normal), 1 (slightly abnormal), 2 (moderately abnormal), and 3 (severely abnormal). Both disease model mouse strains showed high scores even at the apparently pre-symptomatic stage of the disease, particularly with abnormal tail and hind limb postures. Individual and total test scores were well correlated with the progression of the disease. This method is simple, quick, and reproducible. The testing is sensitive enough to detect early neurological abnormalities, and will be useful for monitoring the natural clinical course and effect of therapeutic experiments in various neurogenetic disease model mice, such as chemical chaperone therapy for G(M1)-gangliosidosis model mice.

The Arg482His mutation in the beta-galactosidase gene is responsible for a high frequency of GM1 gangliosidosis carriers in a Cypriot village

GM1 gangliosidosis is a lysosomal storage disorder caused by deficiency of beta-galactosidase. It is mainly characterized by progressive neurodegeneration, and in its most severe infantile form, it leads to death before the age of 4. The GLB1 gene gives rise to two alternatively spliced mRNAs that encode the beta-galactosidase and the elastin binding protein (EBP). The diagnosis of two patients with the infantile form of GM1 gangliosidosis and 11 carriers in a small mountainous village in Cyprus prompted us to carry out a study in order to establish the frequency of carriers in the village and identify the mutations involved. Carrier detection was initially based on the measurement of beta-galactosidase activity in leucocytes. Among 85 random samples from the village, 10 were classified as carriers. Sequencing of the GLB1 gene in a Cypriot patient identified the missense mutation c.1445G>A (p.Arg482His) in the homozygous state. Seven of the 10 carriers identified using the enzyme assay were found to carry the same mutation by NspI restriction enzyme analysis. The three individuals who were negative for the c.1445G>A had borderline enzyme results and were probably wrongly classified as carriers. The frequency of GM1 gangliosidosis carriers in this village is approximately 8% (1:12). Western blot analysis showed a marked decrease of the 64-kDa mature form of the enzyme protein and a similar reduction of the 67-kDa EBP. Our results indicate that the c.1445G>A mutation, which appears to be responsible for all GM1 gangliosidosis alleles in this Cypriot village, affects protein conformation.

GM1-ganglioside-mediated activation of the unfolded protein response causes neuronal death in a neurodegenerative gangliosidosis

GM1-ganglioside (GM1) is a major sialoglycolipid of neuronal membranes that, among other functions, modulates calcium homeostasis. Excessive accumulation of GM1 due to deficiency of lysosomal beta-galactosidase (beta-gal) characterizes the neurodegenerative disease GM1-gangliosidosis, but whether the accumulation of GM1 is directly responsible for CNS pathogenesis was unknown. Here we demonstrate that activation of an unfolded protein response (UPR) associated with the upregulation of BiP and CHOP and the activation of JNK2 and caspase-12 leads to neuronal apoptosis in the mouse model of GM1-gangliosidosis. GM1 loading of wild-type neurospheres recapitulated the phenotype of beta-gal-/- cells and activated this pathway by depleting ER calcium stores, which ultimately culminated in apoptosis. Activation of UPR pathways did not occur in mice double deficient for beta-gal and ganglioside synthase, beta-gal-/-/GalNAcT-/-, which do not accumulate GM1. These findings suggest that the UPR can be induced by accumulation of the sialoglycolipid GM1 and this causes a novel mechanism of neuronal apoptosis.

The leukoencephalopathy of infantile GM1 gangliosidosis: oligodendrocytic loss and axonal dysfunction

A myelin deficit in the cerebral white matter in infantile GM1 gangliosidosis is well established. Some have proposed this deficit to be secondary to axonal loss, while others argue for delayed or arrested myelination. We compared the frontal white and gray matter of two infants with GM1 gangliosidosis with four age-matched controls, using light microscopy with a quantitative analysis, immunohistochemistry, terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL), and electron microscopy (EM). In the GM1 cases, we found a marked decrease in the number of oligodendrocytes (85% in case 1 and 50% in case 2) and myelin sheaths (80% and 40%), with a mild decrease in axons (20% and 10%). Ultrastructurally, some naked axons and dilated cisterns of rough endoplasmic reticulum (RER) in oligodendrocytes were observed. There was no appreciable storage in remaining oligodendrocytes, nor obvious neocortical neuronal loss. An immunohistochemical decrease in proteolipid protein (PLP) and a more profound deficiency of myelin basic protein (MBP) indicate that this lesion is not simply the result of a delay or arrest in myelination and suggests a "dying-back" oligopathy. TUNEL-positive oligodendrocytes correlated with activated caspase-3 immunoreactivity. Amyloid precursor protein (APP)-immunoreactive aggregates were observed in proximal axons and meganeurites as well as in white matter axons. These data suggest that the myelin deficit results from a loss of oligodendrocytes and abnormal axoplasmic transport, perhaps consequent to massive neuronal storage of GM1.

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

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

Galactonojirimycin derivatives restore mutant human beta-galactosidase activities expressed in fibroblasts from enzyme-deficient knockout mouse

Ten low molecular compounds analogous to galactose were screened for inhibition of human beta-galactosidase activity. Among them, 1-deoxy-galactonojirimycin and N-(n-butyl)-deoxy-galactonojirimycin showed an inhibitory effect at high concentrations. However, they restored mutant enzyme activities expressed in enzyme-deficient knockout mouse fibroblasts and human beta-galactosidosis fibroblasts at lower intracellular concentrations. This effect was more remarkable on G(M1)-gangliosidosis mutations (R201C, I51T, R201H, R457Q) than Morquio B disease mutations (W273L, Y83H). These low molecular compounds pass though the blood-brain barrier in mice. We hope that this new therapeutic approach will become clinically applicable in the near future.

Myelination arrest demonstrated using magnetic resonance imaging in a child with type I GM1 gangliosidosis

An 18-month-old girl was diagnosed as having GM1 gangliosidosis, on the basis of the clinical symptoms of muscle stiffness, developmental retardation, hepatosplenomegaly, and kyphoscoliosis and a laboratory study that revealed a deficiency in the lysosomal degradative enzyme beta-galactosidase. Magnetic resonance T1-weighted images showed persistent hyperintensity in the bilateral thalami, brainstem, and deep cerebellum at 14 and 18 months of age, indicating arrest of the myelination process in these areas, and that the arrest had occurred at the newborn stage. There was no myelination in the basal ganglia and diffuse leukomalacia developed in the cerebral hemispheres. Only supportive treatment was given; the patient died at 2 years of age. Myelination arrest at the newborn stage associated with progressive leukomalacia is a possible characteristic of GM1 gangliosidosis.

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.

Profile of electrodiagnostic abnormalities in cats with GM1 gangliosidosis

OBJECTIVE

To determine which electrodiagnostic tests yield abnormal findings in cats with GM1 gangliosidosis, and to determine the approximate age of onset of electrodiagnostic abnormalities.

ANIMALS

Cats (28 to 335 days old) affected with GM1 gangliosidosis (n = 11) and unaffected controls (n = 14).

PROCEDURE

Cats were grouped by age: group 1, < or = 90 days, group 2, 91 to 200 days; and group 3, > 200 days. Electrodiagnostic tests were conducted, including needle electromyography, motor and sensory nerve conduction velocity, spinal evoked potentials, and brainstem auditory evoked potentials. Results for control and affected cats were compared, using the general linear model for ANOVA and Scheffé's test for multiple comparisons.

RESULTS

Needle electromyography did not reveal abnormal spontaneous activity in skeletal muscles of any cat; furthermore, statistical analysis did not indicate significant difference between affected and control groups for nerve conduction velocity, confirming that degeneration of peripheral nerve fibers is not a feature of this disease. However, spinal evoked potentials were abnormal in group-3 cats; conduction velocity within sensory pathways in the cranial part of the spinal cord was significantly slower in GM1-affected cats (P = 0.0002). Brainstem auditory evoked responses also were abnormal: wave V (generated in the region of the pons) had prolonged latency in cats of groups 2 and 3 (P = 0.0003 and 0.0001, respectively, at 90 decibels sound pressure level). In the oldest cats, latencies for earlier waves within the auditory pathway also were prolonged; wave I (generated by the cochlear nerve) was prolonged in group-3 cats (P = 0.0423).

CONCLUSIONS

Motor and sensory nerve conduction velocities remained within normal limits in GM1-affected cats. However, spinal evoked potentials indicated slowing in conduction velocity along the cranial part of the spinal cord in group 3 cats. Brainstem auditory evoked responses indicated prolonged latencies in cats of groups 2 and 3.

Chronic GM1 gangliosidosis presenting as dystonia: clinical and biochemical studies in a new case

Clinical and biochemical findings in a patient affected by chronic GM1 gangliosidosis, presenting as progressive dystonia and mental deterioration, are reported. The patient, a 13-year-old male, showed, at the age of 3 years, an impairment of gait with frequent falls, dysarthria and stuttering. At the age of 6, writing dystonia appeared and subsequently mental deterioration and dystonic postures of arms and legs became evident. The clinical features presented by this patient are similar to those shown by the cases of adult/chronic GM1 gangliosidosis previously reported, except for the early onset. This observation emphasizes the occurrence of dystonia as prominent symptom in chronic GM1 gangliosidosis, underlining that this disease must be considered in the diagnostic approach to the progressive dystonias of the early infancy.