bims-meglyc 2025-12-28 papers

Issue of 2025–12–28
four papers selected by
Silvia Radenkovic, UMC Utrecht

Metabolites. 2025 Dec 08. pii: 786. [Epub ahead of print]15(12):

Multi-Omics Characterization of a Novel SSR4 Variant in Congenital Disorders of Glycosylation.

Nurulamin Abu Bakar, Nurul Izzati Hamzan, Elyssa Milus Majawit, Siti Nurwani Ahmad Ridzuan, Noor Hafizah Hassan, Anasufiza Habib, Lock-Hock Ngu.

Background: Congenital disorders of glycosylation (CDG) are rare inborn errors of metabolism with multisystemic manifestations. SSR4-CDG is an ultra-rare X-linked subtype caused by pathogenic variants in SSR4, a component of the translocon-associated protein (TRAP) complex essential for protein translocation and N-glycosylation. Case presentation: We report a two-year-old Malaysian male presenting with global developmental delay, central hypotonia, microcephaly with complete agenesis of the corpus callosum, recurrent infections, bilateral vesicoureteral reflux, and failure to thrive. Growth parameters (weight, length, and head circumference) were persistently below the expected percentiles, indicating postnatal growth restriction. Initial metabolic and biochemical investigations for global developmental delay were unremarkable, apart from mild hyperammonemia. Transferrin isoform analysis demonstrated a type I CDG pattern, raising suspicion of a glycosylation defect. Results: Transferrin glycopeptide LC-MS/MS showed impaired N-glycan occupancy at both glycosylation sites (Asn432 and Asn630), with reduced fully sialylated glycoforms and increased non-glycosylated peptides. Targeted metabolomics using triple quadrupole LC-MS/MS revealed systemic abnormalities, including elevated arginine and phenylalanine, reduced glutamate, increased lysophosphatidylcholine (C24:0-LPC), and generalized depletion of free and acylcarnitines. Whole-exome sequencing identified a novel hemizygous SSR4 variant (c.98del; p.Pro33LeufsTer23) on the X chromosome, predicted to produce a truncated, nonfunctional protein. Conclusions: This is the first Malaysian patient with SSR4-CDG, comprehensively characterized using a multi-omics diagnostic workflow. The integration of glycoproteomics, metabolomics, and exome sequencing provided a detailed biochemical fingerprint that expands the clinical, genetic, and metabolic spectrum of SSR4-CDG and demonstrates the diagnostic and translational value of multi-omics approaches in inborn errors of metabolism.

Keywords: SSR4; X-linked; congenital disorders of glycosylation (CDG); glycoproteomics; metabolomics; multi-omics

DOI: https://doi.org/10.3390/metabo15120786

Orphanet J Rare Dis. 2025 Dec 23. 20(1): 625

Clinical and genetic characterization of congenital disorders of glycosylation in 20 Chinese patients.

Peiwei Zhao, Li Tan, Qingjie Meng, Lei Zhang, Yufeng Huang, Xiankai Zhang, Yanqiu Hu, Shiqiong Zhou, Xuelian He.

BACKGROUND: Congenital disorders of glycosylation (CDG) are a complex and heterogeneous family of rare metabolic diseases that affect protein and lipid glycosylation and glycosylphosphatidylinositol synthesis. These disorders can affect multiple organs, leading to a broad spectrum of symptoms that vary among different CDG subtypes and between individuals with same type of CDG. This study aimed to investigate the genetic variants, molecular etiologies, and clinical features of 20 Chinese patients diagnosed with CDG.
RESULTS: Using whole-exome sequencing (WES), functional prediction tools, Sanger sequencing, and segregation analysis, we identified variants in several genes: ALG2 (3 patients), DPM2 (3 patients), PMM2 (3 patients), and ALG13 (2 patients). Additionally, variants in COG5, COG6, MOGS, DPM3, ALG1, ALG3, ALG11, SSR4 and SLC35A2 each were observed in single case. In total, 28 distinct variants were identified, 11 of which were previously unreported. Genotype-phenotype correlations revealed notable findings: variants in the N-terminus of ALG2 before the intramembrane domain were associated with congenital myasthenic syndromes (CMS), whereas those in the C-terminus caused ALG2-CDG; DPM2-CDG patients with variants in transmembrane region 1 exhibited more severe phenotypes; male patients with hemizygous variants in SLC35A2 demonstrated milder phenotypes compared to those with mosaic variants.
CONCLUSIONS: This findings expand the spectrum of known clinical presentations and genetic variants in CDG, and establish possible genotype-phenotype correlations of several pathogenic genes, emphasizing the need for functional studies to unravel the underlying mechanisms.

Keywords: Congenital disorders of glycosylation; Genetic variants; Genotype-phenotype correlation; Novel variants; Whole-exome sequencing

DOI: https://doi.org/10.1186/s13023-025-04075-7

J Biol Chem. 2025 Dec 20. pii: S0021-9258(25)02944-8. [Epub ahead of print] 111092

N-linked glycosylation plays an essential role in the stability and function of tissue-nonspecific alkaline phosphatase.

Diana Atanasova, Ali Saad Kusay, Lavanya Moparthi, Stefan Koch, Mathias Haarhaus, Sonoko Narisawa, José Luis Millán, Eva Landberg, Per Magnusson.

Tissue-nonspecific alkaline phosphatase (TNALP) is a membrane-anchored glycoprotein with five N-linked glycosylation sites (N140, N230, N271, N303, N430) that is crucial for bone mineralization. TNALP is released into the bloodstream, serving as a biomarker for bone and mineral disorders. This study explores the role of N-linked glycosylation in the secretion, enzymatic activity, stability, and structure of TNALP. To eliminate the N-linked glycosylation site specifically, a soluble TNALP expression construct was created with the following substitution mutations N140Q, N230Q, N271Q, N303Q and N430D, and expressed in mouse osteoblasts. The effect of glycosylation was also studied by computational modeling (molecular dynamics simulations and the GlycoSHIELD tool). We observed that substituting glycosylation sites reduced TNALP secretion, particularly in the double-site mutations N140Q/N271Q and N230Q/N271Q, due to increased cellular retention. Mutations comprising site N271 (N271Q, N140Q/N271Q, N271Q/N303Q and N271Q/N430D) significantly impaired the enzymatic activity. The computational modeling indicated that N-glycans can stabilize regions of the protein, including the Ca2+-binding domain. Further, interactions between N-glycans can compensate for specific double-site glycan losses. Protein thermal stability analysis showed that, compared to wild-type, N271Q/N430D and N303Q/N430D had increased stability at 56°C. TNALP isoform analysis revealed no differences in isoform patterns for mutations with retained enzymatic activity. The study suggests that N-linked glycosylation, particularly the presence of glycans at N271, is vital for TNALP stability, secretion, and enzymatic function, offering insights into the structural and functional properties of TNALP.

Keywords: Biomarker; N-linked glycosylation; biomineralization; cell-surface enzyme; computer modeling; enzyme kinetics; glycoprotein secretion; molecular dynamics; mutagenesis in vitro; protein stability

DOI: https://doi.org/10.1016/j.jbc.2025.111092

Mol Metab. 2025 Dec 19. pii: S2212-8778(25)00217-0. [Epub ahead of print] 102310

Impaired hepatic metabolism in Hereditary Fructose Intolerance confers fructose-independent risk for steatosis and hypertriglyceridemia.

Melissa A Fulham, John D Griffin, Sylvie Perez, Zhongyuan Sun, Natalie A Daurio, Gang Xing, Michelle F Clasquin, Melissa R Miller, Craig L Hyde, Scott P Kelly, Magalie Boucher, Rachel Poskanzer, Ramya Gamini, Evanthia Pashos, Ying Zhang, Elaine Kuang, Josh Fienman, Kendra K Bence, Gregory J Tesz.

OBJECTIVES: Hereditary fructose intolerance (HFI), caused by Aldolase B deficiency, is a rare genetic disorder where fructose exposure leads to severe metabolic pathologies including Type-2 diabetes and liver steatosis. Despite adhering to fructose-free diets, some individuals still present with disease. Using a rat model of HFI we demonstrate that fructose independent pathologies exist and identify the molecular pathways driving disease.
METHODS: Aldob was deleted in Sprague Dawley rats using CRIPSR/Cas9 (AldoB-KO). Phenotypic, metabolomic and transcriptomic studies were conducted to identify mechanisms promoting fructose-independent pathologies. Potential molecular causes were tested using pharmacologic inhibitors and ASOs.
RESULTS: Deletion of Aldob caused hepatic steatosis, fibrosis and stunted growth in rats weaned on low fructose chow recapitulating human HFI. On fructose-free chow, AldoB-KO rats were phenotypically normal. However, upon fasting, male and female AldoB-KO rats developed hepatic steatosis and hyperlipidemia due to impaired fatty acid oxidation (FAOx) and elevated de novo lipogenesis (DNL). Transcriptional and metabolomic profiling revealed increased hepatic Carbohydrate Response Element Binding Protein (ChREBP) activation in AldoB-KO rats due to glycolytic metabolite accumulation caused by impaired gluconeogenesis. Treatment with Acetyl-CoA Carboxylase (ACC) and Diacylglycerol Acyl Transferase 2 (DGAT2) inhibitors reduced hepatic lipids and plasma triglycerides in AldoB-KO rats. Finally, using electronic health records we observed increased metabolic dysfunction-associated steatohepatitis (MASH) diagnosis in individuals with HFI.
CONCLUSIONS: Aldob deletion caused fructose-independent hyperlipidemia and steatosis upon fasting in rats. Individuals with HFI may have risk for hepatic disease and hyperlipidemia even upon fructose abstinence suggesting additional therapies may be needed to mitigate disease.

DOI: https://doi.org/10.1016/j.molmet.2025.102310