Impaired catabolism of free oligosaccharides due to MAN2C1 variants causes a neurodevelopmental disorder.

Free oligosaccharides (fOSs) are soluble oligosaccharide species generated during N-glycosylation of proteins. Although little is known about fOS metabolism, the recent identification of NGLY1 deficiency, a congenital disorder of deglycosylation (CDDG) caused by loss of function of an enzyme involved in fOS metabolism, has elicited increased interest in fOS processing. The catabolism of fOSs has been linked to the activity of a specific cytosolic mannosidase, MAN2C1, which cleaves α1,2-, α1,3-, and α1,6-mannose residues. In this study, we report the clinical, biochemical, and molecular features of six individuals, including two fetuses, with bi-allelic pathogenic variants in MAN2C1; the individuals are from four different families. These individuals exhibit dysmorphic facial features, congenital anomalies such as tongue hamartoma, variable degrees of intellectual disability, and brain anomalies including polymicrogyria, interhemispheric cysts, hypothalamic hamartoma, callosal anomalies, and hypoplasia of brainstem and cerebellar vermis. Complementation experiments with isogenic MAN2C1-KO HAP1 cells confirm the pathogenicity of three of the identified MAN2C1 variants. We further demonstrate that MAN2C1 variants lead to accumulation and delay in the processing of fOSs in proband-derived cells. These results emphasize the involvement of MAN2C1 in human neurodevelopmental disease and the importance of fOS catabolism.

Bi-allelic variants in the ER quality-control mannosidase gene EDEM3 cause a congenital disorder of glycosylation.

EDEM3 encodes a protein that converts Man8GlcNAc2 isomer B to Man7-5GlcNAc2. It is involved in the endoplasmic reticulum-associated degradation pathway, responsible for the recognition of misfolded proteins that will be targeted and translocated to the cytosol and degraded by the proteasome. In this study, through a combination of exome sequencing and gene matching, we have identified seven independent families with 11 individuals with bi-allelic protein-truncating variants and one individual with a compound heterozygous missense variant in EDEM3. The affected individuals present with an inherited congenital disorder of glycosylation (CDG) consisting of neurodevelopmental delay and variable facial dysmorphisms. Experiments in human fibroblast cell lines, human plasma, and mouse plasma and brain tissue demonstrated decreased trimming of Man8GlcNAc2 isomer B to Man7GlcNAc2, consistent with loss of EDEM3 enzymatic activity. In human cells, Man5GlcNAc2 to Man4GlcNAc2 conversion is also diminished with an increase of Glc1Man5GlcNAc2. Furthermore, analysis of the unfolded protein response showed a reduced increase in EIF2AK3 (PERK) expression upon stimulation with tunicamycin as compared to controls, suggesting an impaired unfolded protein response. The aberrant plasma N-glycan profile provides a quick, clinically available test for validating variants of uncertain significance that may be identified by molecular genetic testing. We propose to call this deficiency EDEM3-CDG.

Long-term enzyme replacement therapy improves neurocognitive functioning and hippocampal synaptic plasticity in immune-tolerant alpha-mannosidosis mice.

Alpha-mannosidosis is a glycoproteinosis caused by deficiency of lysosomal acid alpha-mannosidase (LAMAN), which markedly affects neurons of the central nervous system (CNS), and causes pathognomonic intellectual dysfunction in the clinical condition. Cognitive improvement consequently remains a major therapeutic objective in research on this devastating genetic error. Immune-tolerant LAMAN knockout mice were developed to evaluate the effects of enzyme replacement therapy (ERT) by prolonged administration of recombinant human enzyme. Biochemical evidence suggested that hippocampus may be one of the brain structures that benefits most from long-term ERT. In the present functional study, ERT was initiated in 2-month-old immune-tolerant alpha-mannosidosis mice and continued for 9months. During the course of treatment, mice were trained in the Morris water maze task to assess spatial-cognitive performance, which was related to synaptic plasticity recordings and hippocampal histopathology. Long-term ERT reduced primary substrate storage and neuroinflammation in hippocampus, and improved spatial learning after mid-term (10weeks+) and long-term (30weeks+) treatment. Long-term treatment substantially improved the spatial-cognitive abilities of alpha-mannosidosis mice, whereas the effects of mid-term treatment were more modest. Detailed analyses of spatial memory and spatial-cognitive performance indicated that even prolonged ERT did not restore higher cognitive abilities to the level of healthy mice. However, it did demonstrate marked therapeutic effects that coincided with increased synaptic connectivity, reflected by improvements in hippocampal CA3-CA1 long-term potentiation (LTP), expression of postsynaptic marker PSD-95 as well as postsynaptic density morphology. These experiments indicate that long-term ERT may hold promise, not only for the somatic defects of alpha-mannosidosis, but also to alleviate cognitive impairments of the disorder.

N-Glycosylation of Serum IgG and Total Glycoproteins in MAN1B1 Deficiency.

MAN1B1-CDG has recently been characterized as a type II congenital disorder of glycosylation (CDG), disrupting not only protein N-glycosylation but also general Golgi morphology. Using our high-throughput, quantitative ultra-performance liquid chromatography assay, we achieved a detailed characterization of the glycosylation changes in both total serum glycoproteins and isolated serum IgG from ten previously reported MAN1B1-CDG patients. We have identified and quantified novel hybrid high-mannosylated MAN1B1-CDG-specific IgG glycans and found an increase of sialyl Lewis x (sLex) glycans on serum proteins of all patients. This increase in sLex has not been previously reported in any CDG. These findings may provide insight into the pathophysiology of this CDG.

Cognitive profile and activities of daily living: 35 patients with alpha-mannosidosis.

BACKGROUND: Alpha-mannosidosis (OMIM 248500) (AM) is a rare lysosomal storage disease caused by a deficiency of the alpha-mannosidase enzyme. The typical signs consist of hearing impairment, intellectual disabilities, coarse facial features and motor function disturbances. We report on the cognitive function and activities of daily living in patients with AM. METHODS: Thirty five AM patients, age 6-35 years, were included in the study. As a cognitive function test, we used the Leiter international performance scale-revised (Leiter-R), which consists of two batteries: the visual function and reasoning battery and the memory and attention battery, the latter including a memory screening. Additional two questionnaires, The Childhood Health Assessment Questionnaire (CHAQ) and EQ-5D-5 L, were filled out. RESULTS: We found IQ in the range of 30-81 in our cohort. The total equivalent age (mental age) was significantly reduced, between 3-9 years old for the visual function and reasoning battery, between 2.3-10.2 years for the memory screening. Data suggested a specific developmental profile for AM with a positive intellectual development until the chronological age 10-12 years, followed by a static or slightly increasing intellectual level. All patients were to varying degrees socially and practically dependent and unable to take care of themselves in daily life. CONCLUSIONS: Intellectual disability is a consistent finding in patients with alpha-mannosidosis but with extensive variation. We assess that this group of patients has, despite their intellectual disabilities, a potential for continuous cognitive development, especially during childhood and early teenage years. This should be included and supported in the individual educational planning.

Mannosidase 2, alpha 1 deficiency is associated with ricin resistance in embryonic stem (ES) cells.

Host gene products required for mediating the action of toxins are potential targets for reversing or controlling their pathogenic impact following exposure. To identify such targets libraries of insertional gene-trap mutations generated with a PiggyBac transposon in Blm-deficient embryonic stem cells were exposed to the plant toxin, ricin. Resistant clones were isolated and genetically characterised and one was found to be a homozygous mutant of the mannosidase 2, alpha 1 (Man2α1) locus with a matching defect in the homologous allele. The causality of the molecular lesion was confirmed by removal of the transposon following expression of PB-transposase. Comparative glycomic and lectin binding analysis of the Man2α1 (-/-) ricin resistant cells revealed an increase in the levels of hybrid glycan structures and a reduction in terminal ß-galactose moieties, potential target receptors for ricin. Furthermore, naïve ES cells treated with inhibitors of the N-linked glycosylation pathway at the mannosidase 2, alpha 1 step exhibited either full or partial resistance to ricin. Therefore, we conclusively identified mannosidase 2, alpha 1 deficiency to be associated with ricin resistance.

Cerebellar alterations and gait defects as therapeutic outcome measures for enzyme replacement therapy in α-mannosidosis.

α-Mannosidosis is a rare lysosomal storage disease with accumulation of undegraded mannosyl-linked oligosaccharides in cells throughout the body, most notably in the CNS. This leads to a broad spectrum of neurological manifestations, including progressive intellectual impairment, disturbed motor functions, and cerebellar atrophy. To develop therapeutic outcome measures for enzyme replacement therapy that could be used for human patients, a gene knockout model of α-mannosidosis in mice was analyzed for CNS pathology and motor deficits. In the cerebellar molecular layer, α-mannosidosis mice display clusters of activated Bergman glia, infiltration of phagocytic macrophages, and accumulation of free cholesterol and gangliosides (GM1), notably in regions lacking Purkinje cells. α-Mannosidosis brain lysates also displayed increased expression of Lamp1 and hyperglycosylation of the cholesterol binding protein NPC2. Detailed assessment of motor function revealed age-dependent gait defects in the mice that resemble the disturbed motor function in human patients. Short-term enzyme replacement therapy partially reversed the observed cerebellar pathology with fewer activated macrophages and astrocytes but unchanged levels of hyperglycosylated NPC2, gangliosides, and cholesterol. The present study demonstrates cerebellar alterations in α-mannosidosis mice that relate to the motor deficits and pathological changes seen in human patients and can be used as therapeutic outcome measures.

Alfa-manosidosis tipo II / Alpha-mannosidosis

No disponible

Behavioural characterisation of the alpha-mannosidosis guinea pig.

alpha-Mannosidosis is a lysosomal storage disorder resulting from a functional deficiency of the lysosomal enzyme alpha-mannosidase. This deficiency results in the accumulation of various oligosaccharides in the lysosomes of affected individuals, causing somatic pathology and progressive neurological degeneration that results in cognitive deficits, ataxia, and other neurological symptoms. We have a naturally occurring guinea pig model of this disease which exhibits a deficiency of lysosomal alpha-mannosidase and has a similar clinical presentation to human alpha-mannosidosis. Various tests were developed in the present study to characterise and quantitate the loss of neurological function in alpha-mannosidosis guinea pigs and to follow closely the progression of the disease. General neurological examinations showed progressive differences in alpha-mannosidosis animals from approximately 1 month of age. Significant differences were observed in hind limb gait width from 2 months of age and significant cognitive (memory and learning) deficits were observed from 3 months of age. Evoked response tests showed an increase in somatosensory P1 peak latency in alpha-mannosidosis guinea pigs from approximately 2 months of age, as well as progressive hearing loss using auditory brainstem evoked responses. The alpha-mannosidosis guinea pig therefore appears to exhibit many of the characteristics of the human disease, and will be useful in evaluating therapies for treatment of central nervous system pathology.

Mammalian N-glycan branching protects against innate immune self-recognition and inflammation in autoimmune disease pathogenesis.

Autoimmune diseases are prevalent and often life-threatening syndromes, yet the pathogenic triggers and mechanisms involved remain mostly unresolved. Protein asparagine linked- (N-) glycosylation produces glycan structures that substantially differ among the extracellular compartments of evolutionarily divergent organisms. Alpha-mannosidase-II (alphaM-II) deficiency diminishes complex-type N-glycan branching in vertebrates and induces an autoimmune disease in mice similar to human systemic lupus erythematosus. We found that disease pathogenesis provoking glomerulonephritis and kidney failure was nonhematopoietic in origin, independent of complement C3 and the adaptive immune system, mitigated by intravenous administration of immunoglobulin-G, and linked to chronic activation of the innate immune system. N-glycans produced in alphaM-II deficiency bear immune-stimulatory mannose-dependent ligands for innate immune lectin receptors, disrupting the phylogenic basis of this glycomic recognition mechanism. Thus, mammalian N-glycan branching safeguards against the formation of an endogenous immunologic signal of nonself that can provoke a sterile inflammatory response in the pathogenesis of autoimmune disease.

Bilateral patellar dislocation associated with alpha-mannosidase deficiency.

Mannosidosis is an extremely rare genetic disease characterized by a deficiency of the lysosomal enzyme, alpha-mannosidase. This enzyme is necessary for cleavage of mannose from many glycoproteins. In the absence of this enzyme, mannose accumulates in cells throughout the body, including the joints and the synovium. This disease causes many skeletal changes including dysostosis multiplex, synovial hypertrophy, and Charcot-type joints. We report the case of a girl, aged 9 years and 6 months, who developed bilateral patellar dislocation and severe synovial hypertrophy secondary to alpha-mannosidase deficiency. Her disease was further complicated by Charcot elbow and bilateral hip and elbow avascular necrosis.

Identification and characterization of five novel MAN2B1 mutations in Italian patients with alpha-mannosidosis.

Mutation analysis performed on six Italian families with alpha-mannosidosis type II allowed the identification of five new mutations in the MAN2B1 gene: c.157G>T, c.562C>T, c.599A>T, c.293dupA, c.2402G>A (p.E53X, p.R188X, p.H200L, p.Y99VfsX61, p.G801D). Protein residues G801 and H200 are conserved among the four mammalian alpha-mannosidases cloned to date: human, cattle, cat and mouse. In vitro expression studies demonstrated that both missense mutations expressed no residual alpha-mannosidase activity indicating that they are disease-causing mutations. Modelling into the three-dimensional structure revealed that the p.H200L could involve the catalytic mechanism, whereas p.G801D would affect the correct folding of the enzyme.

Effective gene therapy for an inherited CNS disease in a large animal model.

Genetic diseases affecting the brain typically have widespread lesions that require global correction. Lysosomal storage diseases are good candidates for central nervous system gene therapy, because active enzyme from genetically corrected cells can be secreted and taken up by surrounding diseased cells, and only small amounts of enzyme (<5% of normal) are required to reverse storage lesions. Injection of gene transfer vectors into multiple sites in the mouse brain has been shown to mediate widespread reversal of storage lesions in several disease models. To study a brain closer in size to the human brain, we evaluated the extent of storage correction mediated by a limited number of adeno-associated virus vector injections in the cat model of human alpha-mannosidosis. The treated cats showed remarkable improvements in clinical neurological signs and in brain myelination assessed by quantitative magnetic resonance imaging. Postmortem examination showed that storage lesions were greatly reduced throughout the brain, even though gene transfer was limited to the areas surrounding the injection tracks. The data demonstrate that widespread improvement of neuropathology in a large mammalian brain can be achieved using multiple injection sites during one operation and suggest that this could be an effective treatment for the central nervous system component of human lysosomal enzyme deficiencies.