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

ABSTRACT: 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.

SUBMITTER: Maia N

PROVIDER: S-EPMC8874227 | biostudies-literature | 2022 Feb

REPOSITORIES: biostudies-literature

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

Maia Nuno N Potelle Sven S Yildirim Hamide H Duvet Sandrine S Akula Shyam K SK Schulz Celine C Wiame Elsa E Gheldof Alexander A O'Kane Katherine K Lai Abbe A Sermon Karen K Proisy Maïa M Loget Philippe P Attié-Bitach Tania T Quelin Chloé C Fortuna Ana Maria AM Soares Ana Rita AR de Brouwer Arjan P M APM Van Schaftingen Emile E Nassogne Marie-Cécile MC Walsh Christopher A CA Stouffs Katrien K Jorge Paula P Jansen Anna C AC Foulquier François F

American journal of human genetics 20220118 2

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-, ...[more]

PMID: 35045343

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Project description:BackgroundHeterozygous disruption of FOXP2 causes a rare form of speech and language impairment. Screens of the FOXP2 sequence in individuals with speech/language-related disorders have identified several rare protein-altering variants, but their phenotypic relevance is often unclear. FOXP2 encodes a transcription factor with a forkhead box DNA-binding domain, but little is known about the functions of protein regions outside this domain.MethodsWe performed detailed functional analyses of seven rare FOXP2 variants found in affected cases, including three which have not been previously characterized, testing intracellular localization, transcriptional regulation, dimerization, and interaction with other proteins. To shed further light on molecular functions of FOXP2, we characterized the interaction between this transcription factor and co-repressor proteins of the C-terminal binding protein (CTBP) family. Finally, we analysed the functional significance of the polyglutamine tracts in FOXP2, since tract length variations have been reported in cases of neurodevelopmental disorder.ResultsWe confirmed etiological roles of multiple FOXP2 variants. Of three variants that have been suggested to cause speech/language disorder, but never before been characterized, only one showed functional effects. For the other two, we found no effects on protein function in any assays, suggesting that they are incidental to the phenotype. We identified a CTBP-binding region within the N-terminal portion of FOXP2. This region includes two amino acid substitutions that occurred on the human lineage following the split from chimpanzees. However, we did not observe any effects of these amino acid changes on CTBP binding or other core aspects of FOXP2 function. Finally, we found that FOXP2 variants with reduced polyglutamine tracts did not exhibit altered behaviour in cellular assays, indicating that such tracts are non-essential for core aspects of FOXP2 function, and that tract variation is unlikely to be a highly penetrant cause of speech/language disorder.ConclusionsOur findings highlight the importance of functional characterization of novel rare variants in FOXP2 in assessing the contribution of such variants to speech/language disorder and provide further insights into the molecular function of the FOXP2 protein.

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

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

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