Glycosylation is one of the most important posttranslational modifications. When the glycosylation machinery is affected, this leads to a congenital disorder of glycosylation (CDG). CDG are a class of rare multisystemic diseases that often affect the endoplasmic reticulum (ER). Although vascular complications have been reported in CDG, the contribution of endothelial dysfunction to these phenotypes remains incompletely understood. Here, we evaluated the effect of glycosylation deficiency on endothelial dysfunction by generating two endothelial cell models using pharmacological inhibitors: tunicamycin (a well-known glycosylation inhibitor at the level of DPAGT1), and 2-deoxy-2-fluoro-D-mannose (FMan). This is a novel inhibitor that inhibits mannose and related sugar-phosphate metabolism. These cell models were subjected to transcriptomics, proteomics, and tracer metabolomics to pinpoint the pathways that are most affected across these different levels. Both transcriptomics and proteomics revealed ER stress as the top upregulated feature. This was functionally characterized by decreased cell growth, induced apoptosis, decreased cell migration, and induced an immune response. The barrier function of the cells was not affected. Here, we demonstrate that N-glycosylation deficiency triggers an ER stress response, contributing to endothelial dysfunction, and investigated ER stress mitigation as a potential therapeutic strategy for CDG.

Analyzing single omics and integrating multimodal omics datasets to capture functional dysregulation in disease remains challenging. Here, we propose a bioinformatics framework that leverages curated datasets of protein complexes (‘complexome’) as a foundation for proteomics data integration. Available for human and other model organisms, the complexome provides a global view of cellular function, enabling queries with proteomics datasets. We first benchmarked how protein abundances across human tissues shape distinct complexomic profiles, serving to fingerprint biological activity. Next, we analyzed complexome remodeling using disease versus control proteomics quantifications. Using proteomics data from fibroblasts of patients with genetically confirmed metabolic defects, we identified significant perturbations in mitochondrial oxidative phosphorylation complexes and additional complexes involved in wider mitochondrial functions. The complexome provides a systems-wide approach to dissect mechanisms underlying disease-related functional and phenotypic changes by mapping measured protein-level perturbations to specific molecular complexes. The software is available as a Python notebook at https://github.com/mguharoy/Complexome.

Primary adrenal insufficiency (PAI) in children is rare. It is mainly due to monogenetic disorders, with congenital adrenal hyperplasia being the most common cause in the first year of life. Although several inborn errors of metabolism (IEM) have been associated with PAI, increased awareness of PAI in IEM among both metabolic specialists and endocrinologists may improve patient outcomes. Here, we present a case series of patients with PAI and an IEM. Through a literature review, we discuss the various IEM that have been associated with adrenal insufficiency and explore the pathophysiological mechanisms linking these IEM to PAI. Based on the available data, pitfalls in the diagnosis of PAI in IEM are discussed and recommendations for early diagnosis are suggested. In addition, a non-exhaustive list of susceptible IEM was elaborated to encourage screening for PAI in IEM and vice versa.

Hexose-phosphates play a role in many metabolic pathways, such as glycolysis and glycosylation. To understand the molecular basis of diseases such as congenital disorders of glycosylation (CDG), information about the source and abundance of hexose-phosphates is imperative. Mass spectrometry (MS)-based tracer metabolomics can provide this information, but hexose-phosphates are structural isomers with similar physicochemical properties, which makes them difficult to differentiate using MS. Here, we present and compare two optimized liquid-chromatography-based MS methods for the identification of relevant hexose-phosphates, compatible with tracer metabolomics. A combination of these two methods led to the analysis of eight hexose-monophosphates and two hexose-bisphosphates that can occur in humans. Both methods displayed linearity in 3 to 4 orders of magnitude, with limits of quantification between 0.5 and 50 nM, which is well within the cellular concentration range. The applicability of these methods to biological models was then proven in a study of the effect of galactose treatment in phosphoglucomutase 1 (PGM1)-CDG fibroblasts. Here, we show, for the first time, the hexose-phosphate profiles in CDG and how these change upon treatment.

OBJECTIVE:3-methylglutaconic aciduria (MEG), dystonia-deafness (D), (hepatopathy (H)), encephalopathy (E), and Leigh-like-syndrome (L) (MEGD(H)EL) syndrome is a rare, severely disabling progressive mitochondrial disease associated with biallelic pathogenic variants in SERAC1. Knowledge about hearing loss (HL) and hearing rehabilitation is scarce but highly sought after for best possible care in the absence of causative treatment. METHODS:Retrospective cross-sectional study. RESULTS:This study analyzed the audiometric data of 36 MEGD(H)EL patients (14 unpublished). Bilateral HL was diagnosed in 31 individuals (86 %). Detailed audiometric data, available for 23 of 31 patients, did not allow for general statements on site and degree of HL. HL was mostly congenital (n = 14/31), pre-lingual in six and post-lingual in nine cases (median age 2 years, n = 15/31; age unknown in n = 2). In four of the five patients without HL, the severity of the other clinical-neurological symptoms was milder and less progressive, and their onset was significantly later than in the patients with HL. Five of 36 patients acquired spoken language, these were 4 of the 5 individuals without and one with HL. Twenty-two individuals received hearing rehabilitation with conventional hearing aids, followed by cochlear implant (CI) surgery in six. One of these six individuals acquired spoken language, which lessened in clarity as disease progressed. CONCLUSIONS:Congenital HL represents a ubiquitous symptom in severe types of MEGD(H)EL syndrome, being absent in late onset milder forms. Regularly, severely affected MEGD(H)EL patients do not achieve spoken language, even with CI. Hence, hearing rehabilitation with CIs needs to be discussed very critically.

SLC35A2-CDG is an X-linked congenital disorder of glycosylation (CDG), characterized by defective UDP-galactose transport into the Golgi and endoplasmic reticulum and consequent insufficient galactosylation of glycans. Clinically, this translates into a range of predominantly neurological symptoms. Although the pathomechanism of this disorder is not fully understood, oral galactose supplementation has led to clinical and biochemical improvement in some patients. Here, we show that protein glycosylation (N- and O-linked) was only minimally disturbed in SLC35A2-CDG patient-derived fibroblasts. However, lipid glycosylation was significantly impaired, with accumulation of glucosylceramide and deficiency of digalactosylated glycosphingolipids (GSLs) and complex gangliosides. Galactose supplementation increased UDP-galactose, its transport into the Golgi, and improved deficient GSL synthesis through direct incorporation of the provided galactose. This improved GSL homeostasis in all patient-derived fibroblasts and in another SLC35A2 deficient cell model (CHO-Lec8). Additionally, SLC35A2-CDG serum analysis identified hydroxylated GSLs, particularly GM3, as potential disease biomarkers. Given the essential role of gangliosides in central nervous system function, their deficiency is likely a key factor in the neurological involvement of this disorder. These findings pave the way for new nutritional therapies with GSL supplements and highlight the importance of studying lipid glycosylation to better understand the complex pathophysiology of CDG.

Neuroblastomas represent a diverse group of neuroblastic tumors characterized by variability in their clinical progression and degree of differentiation. In rare cases, patients with neuroblastoma may present with paraneoplastic syndromes, such as watery diarrhea, hypokalemia, and achlorhydria (WDHA syndrome), linked to the secretion of vasoactive intestinal peptide (VIP). We report a case of a 14-month-old girl presented with a three-week history of watery diarrhea and signs of dehydration with no other symptoms. The patient's medical history was unremarkable, and no medication use was reported. Venous blood gas analysis revealed a normal anion gap metabolic acidosis with severe hypokalemia. The patient was referred to our hospital 48 hours post-admission due to persistent hypokalemic metabolic acidosis, unresponsive to intravenous fluid therapy. The primary causes of normal anion gap metabolic acidosis in young children are gastrointestinal bicarbonate loss due to diarrhea and renal bicarbonate loss. Semi-quantitative urine organic acid analysis, reported 48 hours after admission, revealed increased vanillylmandelic acid (VMA) (89 mmol/mol creatinine) and homovanillic acid (HVA) (21 mmol/mol creatinine), raising the suspicion of a neuroblastoma. Subsequent analysis of an acidified urine sample confirmed a more than threefold increase in VMA, HVA, normetanephrine, norepinephrine, and 3-methoxytyramine concentrations. In addition, VIP was markedly elevated (1994 ng/L) in a blood sample. The diagnosis of neuroblastoma was confirmed through imaging and histological examination. This case illustrates that chronic diarrhea with metabolic dysregulation (e.g. hypokalemia) can be the first and only symptom in patients with VIP-secreting neuroblastoma which can result in delayed diagnosis of neuroblastoma.

Acid sphingomyelinase deficiency (ASMD) is a rare lysosomal storage disease characterized by hepatosplenomegaly, pulmonary dysfunction, dyslipidemia, and growth deficits. Olipudase alfa (recombinant-human ASM) is the only treatment for non-central-nervous-system ASMD manifestations in children and adults. An open-label long-term study followed 4 to 8 years of olipudase alfa treatment in 20 children and adolescents with ASMD (baseline age (years) 1.5-17.5). At final assessments, splenomegaly and hepatomegaly were reduced relative to baseline (mean percent decrease in spleen and liver volumes 78% ± 1.2% and 59.8% ± 1.5%, respectively). Baseline splenomegaly was severe (spleen volume > 15 MN [multiples of normal]) or moderate (5-15 MN) (n = 12 and n = 8, respectively) versus mild/absent (< 5 MN) (n = 12) or moderate (n = 8) at final assessment. Baseline hepatomegaly was severe (liver volume > 2.5 MN) (n = 10) or moderate (1.25-2.5 MN) (n = 10) versus mild/absent (< 1.25 MN) (n = 19) or moderate (n = 1) at final assessment. Among nine individuals able to perform assessments, diffusing capacity of the lung for carbon monoxide (DLCO) impairment was severe (< 40%) (n = 1), moderate (40%-60%) (n = 4), or mild (60%-80%) (n = 4) at baseline versus absent (n = 4), mild (n = 4) or moderate (n = 1) at final assessment. Mean percent increase in DLCO was 53.7% ± 6.5%. At baseline, 10/20 children had clinical short stature (height Z-scores ≤ - 2) at baseline versus 0/20 at the final assessment. Atherogenic lipid profiles and liver function tests normalized within 2 years and remained stable. Adverse events were mostly mild or moderate, with 4 individuals experiencing 7 serious adverse events, all recovered/resolved. Interpretation: Enzyme replacement therapy with olipudase alfa in children and adolescents with chronic ASMD was well-tolerated with clinically meaningful improvements in multiple disease parameters. Trial Registration: NCT02004704.

Erythropoietic protoporphyria (EPP) is an inherited metabolic disease that causes painful phototoxic reactions, starting in childhood. Studies have shown a reduced quality of life (QoL) in adults with EPP, however, data on children with the disease are lacking. Since treatment for EPP is currently not registered for children, knowledge about their QoL is of crucial importance. In this prospective, case-control study, we included children from the Netherlands and Belgium diagnosed with EPP and matched to healthy controls. Previously collected EPP quality of life (EPP-QoL) data from matched adults with EPP were used. QoL scores, utilizing the Pediatric Quality of Life Inventory (PedsQL) and the disease-specific EPP-QoL, were collected. Scores range from 0 to 100, with higher scores indicating a higher QoL. Non-parametric tests were used to compare groups. A total of 15 cases, 13 matched healthy control children, and 15 matched adults with EPP were included. Children with EPP exhibited lower median scores in the PedsQL in both physical (cases: 87.5 (interquartile range [IQR] 77.7-96.1), controls: 99.2 [IQR 94.9-100.0], p = 0.03) and social (cases: 77.5 [IQR 69.4-86.3], controls: 97.5 [IQR 78.8-100.0], p = 0.04) domains compared to healthy children, although these differences were not statistically significant after correcting for multiple testing. The overall median EPP-QoL score for children was similar to adults with EPP (children: 44.4 [IQR 25.0-54.2], adults: 45.8 [IQR 25.7-68.1], p = 0.68). However, within the EPP-QoL subdomain on QoL, children were found to have significantly lower median scores (children: 16.7 [IQR 0.0-33.3], adults: 33.3 [IQR 33.3-62.5], p < 0.01). In conclusion, children with EPP experience a reduced QoL compared to both healthy children and adults with EPP. Ensuring treatment availability for this patient group is crucial for improving their QoL. We advocate the inclusion of children in safety and efficacy studies, to ensure availability of treatment in the future.

Alkaptonuria is characterized by the accumulation of homogentisic acid which causes dark coloration of urine upon standing, ochronosis, and arthritis. A 4-year old child was referred to our pediatric nephrologist with hyperoxaluria and a history of unexplained pink-to-brown discolouration of his diapers associated with a brown-staining of clothes and skin since he was six months old. He had no other symptoms and his past medical history only included minor child illnesses. His 11-month-old brother had the same dark discoloration of his diapers. Laboratory testing on a spot urine sample showed hyperoxaluria and nephrotic range proteinuria with low creatinine and normal albumin concentrations. Considered causes were hyperoxaluria, alkaptonuria, interfering substance, adulteration. The further diagnostic work-up revealed increased homogentisic acid in urine, compatible with alkaptonuria. Urinary creatinine and total protein measurements on Roche Cobas were, respectively, falsely decreased and increased in the presence of homogentisic acid. The false-low creatinine resulted in an elevated oxalate/creatinine ratio. Alkaptonuria can cause a false increase of results expressed per creatinine and should be excluded in case of an unexplained marked increase of urine total protein without a concomitant increase of albumin.

We report on the largest single dataset of patients with PMM2-CDG enrolled in an ongoing international, multicenter natural history study collecting genetic, clinical, and biological information to evaluate similarities with previous studies, report on novel findings, and, additionally, examine potential genotype/phenotype correlations. A total of 137 participants had complete genotype information, representing 60 unique variants, of which the most common were found to be p.Arg141His in 58.4% (n = 80) of participants, followed by p.Pro113Leu (21.2%, n = 29), and p.Phe119Leu (12.4%, n = 17), consistent with previous studies. Interestingly, six new variants were reported, comprised of five missense variants (p.Pro20Leu, p.Tyr64Ser, p.Phe68Cys, p.Tyr76His, and p.Arg238His) and one frameshift (c.696del p.Ala233Argfs∗100). Patient phenotypes were characterized via the Nijmegen Progression CDG Rating Scale (NPCRS), together with biochemical parameters, the most consistently dysregulated of which were coagulation factors, specifically antithrombin (below normal in 79.5%, 93 of 117), in addition to Factor XI and protein C activity. Patient genotypes were classified based upon the predicted pathogenetic mechanism of disease-associated mutations, of which most were found in the catalysis/activation, folding, or dimerization regions of the PMM2 enzyme. Two different approaches were used to uncover genotype/phenotype relationships. The first characterized genotype only by the predicted pathogenic mechanisms and uncovered associated changes in biochemical parameters, not apparent using only NPCRS, involving catalysis/activation, dimerization, folding, and no protein variants. The second approach characterized genotype by the predicted pathogenic mechanism and/or individual variants when paired with a subset of severe nonfunctioning variants and uncovered correlations with both NPCRS and biochemical parameters, demonstrating that p.Cys241Ser was associated with milder disease, while p.Val231Met, dimerization, and folding variants with more severe disease. Although determining comprehensive genotype/phenotype relationships has previously proven challenging for PMM2-CDG, the larger sample size, plus inclusion of biochemical parameters in the current study, has provided new insights into the interplay of genetics with disease. Trial Registration: NCT03173300.

OBJECTIVE:Our report describes clinical, genetic, and biochemical features of participants with a molecularly confirmed congenital disorder of glycosylation (CDG) enrolled in the Frontiers in Congenital Disorders of Glycosylation (FCDGC) Natural History cohort at year 5 of the study. METHODS:We enrolled individuals with a known or suspected CDG into the FCDGC Natural History Study, a multicenter prospective and retrospective natural history study of all genetic causes of CDG. We conducted a cross-sectional analysis of baseline study visit data from participants with confirmed CDG who were consented into the FCDGC Natural History Study (5U54NS115198) from October 2019 to November 2023. RESULTS:Three hundred thirty-three subjects consented to the FCDGC Natural History Study. Of these, 280 unique individuals had genetic data available that was consistent with a diagnosis of CDG. These 280 individuals were enrolled into the study between October 8, 2019 and November 29, 2023. One hundred forty-one (50.4%) were female, and 139 (49.6%) were male. Mean and median age at enrollment was 10.1 and 6.5 years, respectively, with a range of 0.22 to 71.4 years. The cohort encompassed individuals with disorders of N-linked protein glycosylation (57%), glycosylphosphatidylinositol anchor disorder (GPI anchor) (15%), disorders of Golgi homeostasis, trafficking and transport (12%), dolichol metabolism disorders (5%), disorders of multiple pathways (6%), and other (5%). The most frequent presenting symptom(s) leading to diagnosis were developmental delay/disability (77%), followed by hypotonia (56%) and feeding difficulties (42%). Mean and median time between first related symptom and diagnosis was 2.7 and 0.8 years, respectively. One hundred percent of individuals in our cohort had developmental differences/disabilities at the time of their baseline visit, followed by 97% with neurologic involvement, 91% with gastrointestinal (GI)/liver involvement, and 88% with musculoskeletal involvement. Severity of disease in individuals was scored on the Nijmegen Progression CDG Rating Scale (NPCRS) with 27% of scores categorized as mild, 44% moderate, and 29% severe. Of the individuals with N-linked protein glycosylation defects, 83% of those with data showed a type 1 pattern on carbohydrate deficient transferrin (CDT) analysis including 82/84 individuals with PMM2-CDG, 6% a type 2 pattern, 1% both type 1 and type 2 pattern and 10% a normal or nonspecific pattern. One hundred percent of individuals with Golgi homeostasis and trafficking defects with data showed a type 2 pattern on CDT analysis, while Golgi transport defect showed a type II pattern 73% of the time, a type 1 pattern for 7%, and 20% had a normal or nonspecific pattern. Most of the variants documented were classified as pathogenic or likely pathogenic using ACMG criteria. For the majority of the variants, the predicted molecular consequence was missense followed by nonsense and splice site, and the majority of the diagnoses are inherited in an autosomal recessive pattern but with disorders of all major nuclear inheritance included. DISCUSSION:The FCDGC Natural History Study serves as an important resource to build future research studies, improve clinical care, and prepare for clinical trial readiness. Herein is the first overview of CDG participants of the FCDGC Natural History Study.

BACKGROUND & AIMS:Cystic fibrosis (CF) is considered a multisystemic disorder in which CF-associated liver disease (CFLD) is the third most common cause of mortality. Currently, no effective treatment is available for CFLD because its pathophysiology is still unclear. Interestingly, CFLD exhibits identical vascular characteristics as non-cirrhotic portal hypertension, recently classified as porto-sinusoidal vascular disorders (PSVD). METHODS:Since endothelial cells (ECs) are an important component in PSVD, we performed single-cell RNA sequencing (scRNA-seq) on four explant livers from CFLD patients to identify differential endothelial characteristics which could contribute to the disease. We comprehensively characterized the endothelial compartment and compared it with publicly available scRNA-seq datasets from cirrhotic and healthy livers. Key gene signatures were validated ex vivo on patient tissues. RESULTS:We found that ECs from CF liver explants are more closely related to healthy than cirrhotic patients. In CF patients we also discovered a distinct population of liver sinusoidal ECs-coined CF LSECs-upregulating genes involved in the complement cascade and coagulation. Finally, our immunostainings further validated the predominant periportal location of CF LSECs. CONCLUSIONS:Our work showed novel aspects of human liver ECs at the single-cell level thereby supporting endothelial involvement in CFLD, and reinforcing the hypothesis that ECs could be a driver of PSVD. Therefore, considering the vascular compartment in CF and CFLD may help developing new therapeutic approaches for these diseases.

Cardiac involvement (CI) in phosphomannomutase 2-congenital disorders of glycosylation (PMM2-CDG) is part of the multisystemic presentation contributing to high mortality rates. The most common cardiac manifestations are pericardial effusion, cardiomyopathy, and structural heart defects. A genotype-phenotype correlation with organ involvement has not yet been described. We analyzed clinical, biochemical, and molecular genetic data of 222 patients from eight European centers and characterized the natural course of patients with CI. Fifty-seven patients (45 children) presented with CI, of whom 24 died (median age 21 months, standard deviation 49.8). Pericardial effusion was the most frequent manifestation (55.4%), occurring mostly within the first 6 months of life. The most common pathogenic variants in patients with CI were p.(Arg141His) in 74%, followed by p.(Val231Met) in 36%, which is 3.5 times higher than in PMM2-CDG patients without CI (p < 0.0001). Twenty-one out of 36 patients with p.(Val231Met) had CI; among them, 15 died, compared to 33 out of 166 patients without p.(Val231Met) who had CI (p < 0.0001). Nine out of 33 patients died (p = 0.0015), indicating greater clinical severity. Furthermore, the p.(Val231Met) variant is predominant in Eastern Europe, suggesting a founder effect. Cardiac complications in PMM2-CDG patients are common and serious. The variant p.(Val231Met) profoundly influences the extent of CI and mortality rates. Therefore, we recommend cardiac surveillance be included in the follow-up protocols for PMM2-CDG.

Congenital disorders of glycosylation (CDG) are a large family of rare disorders affecting the different glycosylation pathways. Defective glycosylation can affect any organ, with varying symptoms among the different CDG. Even between individuals with the same CDG there is quite variable severity. Associating specific symptoms to deficiencies of certain glycoproteins or glycolipids is thus a challenging task. In this review, we focus on the glycosphingolipid (GSL) synthesis pathway, which is still rather unexplored in the context of CDG, and outline the functions of the main GSLs, including gangliosides, and their role in the central nervous system. We provide an overview of GSL studies that have been performed in CDG and show that abnormal GSL levels are not only observed in CDG directly affecting GSL synthesis, but also in better known CDG, such as PMM2-CDG. We highlight the importance of studying GSLs in CDG in order to better understand the pathophysiology of these disorders.