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Phosphomannomutase 2 deficiency (PMM2-CDG), the most frequent congenital disorder of glycosylation, is an autosomal recessive disease caused by biallelic pathogenic variants in the PMM2 gene. There is no cure for this multisystemic syndrome. Some of the therapeutic approaches that are currently in development include mannose-1-phosphate replacement therapy, drug repurposing, and the use of small chemical molecules to correct folding defects. Preclinical models are needed to evaluate the efficacy of treatments to overcome the high lethality of the available animal model. In addition, the number of variants with unknown significance is increasing in clinical settings. This study presents the generation of a cellular disease model by knocking out the PMM2 gene in the hepatoma HepG2 cell line using CRISPR-Cas9 gene editing. The HepG2 knockout model accurately replicates the PMM2-CDG phenotype, exhibiting a complete absence of PMM2 protein and mRNA, a 90% decrease in PMM enzymatic activity, and altered ICAM-1, LAMP1 and A1AT glycoprotein patterns. The evaluation of PMM2 disease-causing variants validates the model's utility for studying new PMM2 clinical variants, providing insights for diagnosis and potentially for evaluating therapies. A CRISPR-Cas9-generated HepG2 knockout model accurately recapitulates the PMM2-CDG phenotype, providing a valuable tool for assessing disease-causing variants and advancing therapeutic strategies.

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Transferrin isoform analysis is an established laboratory test for congenital disorders of glycosylation (CDG). Despite its long history of clinical use, little has been published about its empirical sensitivity for specific conditions. We conducted a retrospective analysis of ten years of testing data and report our experience with transferrin testing for type I profiles and its sensitivity for the most common congenital disorder of glycosylation, PMM2-CDG. The data demonstrate 94% overall test sensitivity for PMM2-CDG and importantly demonstrate two known, recurrent variants enriched in false positive cases highlighting an important limitation of the test. The data confirm the clinical validity of transferrin isotype analysis as a screening test for disorders of protein N-linked glycosylation and as functional test for PMM2 genotypes of uncertain significance.

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The role of N-glycosylation in the myogenic process remains poorly understood. Here, we evaluated the impact of N-glycosylation inhibition by Tunicamycin (TUN) or by phosphomannomutase 2 (PMM2) gene knockdown, which encodes an enzyme essential for catalyzing an early step of the N-glycosylation pathway, on C2C12 myoblast differentiation. The effect of chronic treatment with TUN on tibialis anterior (TA) and extensor digitorum longus (EDL) muscles of WT and MLC/mIgf-1 transgenic mice, which overexpress muscle Igf-1Ea mRNA isoform, was also investigated. TUN-treated and PMM2 knockdown C2C12 cells showed reduced ConA, PHA-L, and AAL lectin binding and increased ER-stress-related gene expression (Chop and Hspa5 mRNAs and s/uXbp1 ratio) compared to controls. Myogenic markers (MyoD, myogenin, and Mrf4 mRNAs and MF20 protein) and myotube formation were reduced in both TUN-treated and PMM2 knockdown C2C12 cells. Body and TA weight of WT and MLC/mIgf-1 mice were not modified by TUN treatment, while lectin binding slightly decreased in the TA muscle of WT (ConA and AAL) and MLC/mIgf-1 (ConA) mice. The ER-stress-related gene expression did not change in the TA muscle of WT and MLC/mIgf-1 mice after TUN treatment. TUN treatment decreased myogenin mRNA and increased atrogen-1 mRNA, particularly in the TA muscle of WT mice. Finally, the IGF-1 production and IGF1R signaling pathways activation were reduced due to N-glycosylation inhibition in TA and EDL muscles. Decreased IGF1R expression was found in TUN-treated C2C12 myoblasts which was associated with lower IGF-1-induced IGF1R, AKT, and ERK1/2 phosphorylation compared to CTR cells. Chronic TUN-challenge models can help to elucidate the molecular mechanisms through which diseases associated with aberrant N-glycosylation, such as Congenital Disorders of Glycosylation (CDG), affect muscle and other tissue functions.

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PMM2-CDG is the most common congenital disorder of glycosylation (CDG). Patients with this disease often carry compound heterozygous mutations of the gene encoding the phosphomannomutase 2 (PMM2) enzyme. PMM2 converts mannose-6-phosphate (M6P) to mannose-1-phosphate (M1P), which is a critical upstream metabolite for proper protein N-glycosylation. Therapeutic options for PMM2-CDG patients are limited to management of the disease symptoms, as no drug is currently approved to treat this disease. GLM101 is a M1P-loaded liposomal formulation being developed as a candidate drug to treat PMM2-CDG. This report describes the effect of GLM101 treatment on protein N-glycosylation of PMM2-CDG patient-derived fibroblasts. This treatment normalized intracellular GDP-mannose, increased the relative glycoprotein mannosylation content and TNFα-induced ICAM-1 expression. Moreover, glycomics profiling revealed that GLM101 treatment of PMM2-CDG fibroblasts resulted in normalization of most high mannose glycans and partial correction of multiple complex and hybrid glycans. In vivo characterization of GLM101 revealed its favorable pharmacokinetics, liver-targeted biodistribution, and tolerability profile with achieved systemic concentrations significantly greater than its effective in vitro potency. Taken as a whole, the results described in this report support further exploration of GLM101's safety, tolerability, and efficacy in PMM2-CDG patients.

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Phosphomannomutase 2 (PMM2) converts mannose-6-phospahate to mannose-1-phosphate; the substrate for GDP-mannose, a building block of the glycosylation biosynthetic pathway. Pathogenic variants in the PMM2 gene have been shown to be associated with protein hypoglycosylation causing PMM2-congenital disorder of glycosylation (PMM2-CDG). While mannose supplementation improves glycosylation in vitro, but not in vivo, we hypothesized that liposomal delivery of mannose-1-phosphate could increase the stability and delivery of the activated sugar to enter the targeted compartments of cells. Thus, we studied the effect of liposome-encapsulated mannose-1-P (GLM101) on global protein glycosylation and on the cellular proteome in skin fibroblasts from individuals with PMM2-CDG, as well as in individuals with two N-glycosylation defects early in the pathway, namely ALG2-CDG and ALG11-CDG. We leveraged multiplexed proteomics and N-glycoproteomics in fibroblasts derived from different individuals with various pathogenic variants in PMM2, ALG2 and ALG11 genes. Proteomics data revealed a moderate but significant change in the abundance of some of the proteins in all CDG fibroblasts upon GLM101 treatment. On the other hand, N-glycoproteomics revealed the GLM101 treatment enhanced the expression levels of several high-mannose and complex/hybrid glycopeptides from numerous cellular proteins in individuals with defects in PMM2 and ALG2 genes. Both PMM2-CDG and ALG2-CDG exhibited several-fold increase in glycopeptides bearing Man6 and higher glycans and a decrease in Man5 and smaller glycan moieties, suggesting that GLM101 helps in the formation of mature glycoforms. These changes in protein glycosylation were observed in all individuals irrespective of their genetic variants. ALG11-CDG fibroblasts also showed increase in high mannose glycopeptides upon treatment; however, the improvement was not as dramatic as the other two CDG. Overall, our findings suggest that treatment with GLM101 overcomes the genetic block in the glycosylation pathway and can be used as a potential therapy for CDG with enzymatic defects in early steps in protein N-glycosylation.

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CONTEXT: In cellular environments, the reduction of disulfide bonds is pivotal for protein folding and synthesis. However, the intricate enzymatic mechanisms governing this process remain poorly understood. This study addresses this gap by investigating a disulfide bridge reduction reaction, serving as a model for comprehending electron and proton transfer in biological systems. Six potential mechanisms for reducing the dimethyl disulfide (DMDS) bridge through electron and proton capture were explored. Thermodynamic and kinetic analyses elucidated the sequence of proton and electron addition. MD-PMM, a method that combines molecular dynamics simulations and quantum-chemical calculations, was employed to compute the redox potential of the mechanism. This research provides valuable insights into the mechanisms and redox potentials involved in disulfide bridge reduction within proteins, offering an understanding of phenomena that are challenging to explore experimentally. METHODS: All calculations used the Gaussian 09 software package at the MP2/6-311 + g(d,p) theory level. Visualization of the molecular orbitals and electron densities was conducted using Gaussview6. Molecular dynamics simulations were performed using GROMACS with the CHARMM36 force field. The PyMM program (Python Program for QM/MM Simulations Based on the Perturbed Matrix Method) is used to apply the Perturbed Matrix Method to MD simulations.

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PMM2-CDG (MIM # 212065), the most common congenital disorder of glycosylation, is caused by the deficiency of phosphomannomutase 2 (PMM2). It is a multisystemic disease of variable severity that particularly affects the nervous system; however, its molecular pathophysiology remains poorly understood. Currently, there is no effective treatment. We performed an RNA-seq based transcriptomic study using patient-derived fibroblasts to gain insight into the mechanisms underlying the clinical symptomatology and to identify druggable targets. Systems biology methods were used to identify cellular pathways potentially affected by PMM2 deficiency, including Senescence, Bone regulation, Cell adhesion and Extracellular Matrix (ECM) and Response to cytokines. Functional validation assays using patients' fibroblasts revealed defects related to cell proliferation, cell cycle, the composition of the ECM and cell migration, and showed a potential role of the inflammatory response in the pathophysiology of the disease. Furthermore, treatment with a previously described pharmacological chaperone reverted the differential expression of some of the dysregulated genes. The results presented from transcriptomic data might serve as a platform for identifying therapeutic targets for PMM2-CDG, as well as for monitoring the effectiveness of therapeutic strategies, including pharmacological candidates and mannose-1-P, drug repurposing.

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Vitamin C plays an important role in plant antioxidation, photosynthesis, growth and development, and metabolism. In this study, a gene AhPMM, which is involved in vitamin C synthesis and responds significantly to low temperature, NaCl, polyethylene glycol (PEG) and abscisic acid (ABA) treatments, was cloned from peanut. An AhPMM overexpression vector was constructed, and transferred to a peanut variety Junanxiaohong using the pollen tube injection method. PCR test on the T3 generation transgenic peanut plants showed a transgenics positive rate of 42.3%. HPLC was used to determine the content of reducing vitamin C (AsA) and total vitamin C in the leaves of transgenic plants. The results showed that the content of AsA in some lines increased significantly, up to 1.90 times higher than that of the control, and the total vitamin content increased by up to 1.63 times compared to that of the control. NaCl and ABA tolerance tests were carried out on transgenic seeds. The results showed that the salt tolerance of transgenic seeds was significantly enhanced and the sensitivity to ABA was weakened compared to that of the non-transgenic control. Moreover, the salt tolerance of the transgenic plants was also significantly enhanced compared to that of the non-transgenic control. The above results showed that AhPMM gene not only increased the vitamin C content of peanut, but also increased the salt tolerance of transgenic peanut seeds and plants. This study may provide a genetic source for the molecular breeding of peanut for enhanced salt tolerance.

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In a recent paper, we proposed a scheme to describe the relaxation mechanism of the excited Indole in aqueous solution, involving the fluctuations among the diabatic electronic states 1Lb, 1La and 1πσ∗. Such a theoretical and computational model reproduced accurately the available experimental data at room temperature. Following these results, in the present work, we model the complex temperature dependence of the fluorescence properties of Indole in aqueous solution, with results further validating the proposed relaxation scheme. This scheme is able to explain the temperature effects on the fluorescence behavior indicating the water fluctuations as the main cause of (i) the stabilization of the dark state (1πσ∗) and (ii) the increase in temperature of the kinetics of the irreversible transition towards such a state.

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Glycosylation is a critical post-translational modification that plays a pivotal role in several biological processes, such as the immune response. Alterations in glycosylation can modulate the course of various pathologies, such as the case of congenital disorders of glycosylation (CDG), a group of more than 160 rare and complex genetic diseases. Although the link between glycosylation and immune dysfunction has already been recognized, the immune involvement in most CDG remains largely unexplored and poorly understood. In this study, we provide an update on the immune dysfunction and clinical manifestations of the 12 CDG with major immune involvement, organized into 6 categories of inborn errors of immunity according to the International Union of Immunological Societies (IUIS). The immune involvement in phosphomannomutase 2 (PMM2)-CDG - the most frequent CDG - was comprehensively reviewed, highlighting a higher prevalence of immune issues during infancy and childhood and in R141H-bearing genotypes. Finally, using PMM2-CDG as a model, we point to links between abnormal glycosylation patterns in host cells and possibly favored interactions with microorganisms that may explain the higher susceptibility to infection. Further characterizing immunopathology and unusual host-pathogen adhesion in CDG can not only improve immunological standards of care but also pave the way for innovative preventive measures and targeted glycan-based therapies that may improve quality of life for people living with CDG.

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OBJECTIVE: The aim of this study was to assess the effect of a six-month interval rehabilitation treatment on motor function of children with PMM2-CDG syndrome (#212065 Congenital disorder of glycosylation, Type Ia; CDG1A, OMIM catalogue number). METHODS: The concept 'Auf die Beine' (Center for Prevention and Rehabilitation of the University of Cologne, Germany) combines two short inpatient stays (1 to 2 weeks) with a six-month whole-body vibration (WBV) home-training program. 13 patients with PMM2-CDG syndrome participated in this concept from 2006 until 2015. Assessments at start, six months and 12 months (follow-up): Gross Motor Function Measure (GMFM-66), One-Minute Walk Test (1MWT) and instrumented gait analyses. RESULTS: The GMFM-66 (9 of 13 children) improved by 5.3 (mean) points (SD 3.2) at 12 months (p=0.0039). The 1MWT (6 of 13 children) improved by 19.17 meter (SD 16.51) after 12 months (p=0.0313). Gait analysis (9 of 13 children) measured by pathlength/distance ratio improved by -0.8 (SD 1.9) at 12 months (p=0.0195). CONCLUSION: Patients with PMM2-CDG syndrome benefit from the interval rehabilitation program 'Auf die Beine' including WBV.

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BACKGROUND: Congenital disorders of glycosylation (CDG) are genetic diseases caused by impaired synthesis of glycan moieties linked to glycoconjugates. Phosphomannomutase 2 deficiency (PMM2-CDG), the most frequent CDG, is characterized by prominent neurological involvement. Gait disturbance is a major cause of functional disability in patients with PMM2-CDG. However, no specific gait assessment for PMM2-CDG is available. This study analyses gait-related parameters in PMM2-CDG patients using a standardized clinical assessment and instrumented gait analysis (IGA). RESULTS: Seven adult patients with a molecular diagnosis of PMM2-CDG were followed-up from February 2021 to December 2022 and compared to a group of healthy control (HC) subjects, matched for age and sex. Standardized assessment of disease severity including ataxia and peripheral neuropathy along with isometric muscle strength and echo-biometry measurements at lower limbs were performed. IGA spatiotemporal parameters were obtained by means of a wearable sensor in basal conditions. PMM2-CDG patients displayed lower gait speed, stride length, cadence and symmetry index, compared to HC. Significant correlations were found among the used clinical scales and between disease severity (NCRS) scores and the gait speed measured by IGA. Variable reduction of knee extension strength and a significant decrease of lower limb muscle thickness with conserved echo intensity were found in PMM2-CDG compared to HC. CONCLUSIONS: The study elucidates different components of gait disturbance in PMM2-CDG patients and shows advantages of using wearable sensor-based IGA in this frame. IGA parameters may potentially serve as quantitative measures for follow-up or outcome quantification in PMM2-CDG.

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PURPOSE: Metabolic reprogramming in breast cancer (BC) subtypes offers potential personalized treatment targets. Estrogen receptor α (ERα)-positive BC patients undergoing endocrine therapy (ET) can develop ET-resistant metastatic disease. Specific mutations, like Y537S in ERα, drive uncontrolled cell proliferation. Targeting mutant receptor levels shows promise for inhibiting growth in metastatic BC expressing ERα variants. Additionally, metabolic reprogramming occurs in ERα Y537S mutant cells. Consequently, we conducted a screen to identify metabolic proteins reducing intracellular levels of ERα Y537S and inhibiting cell proliferation. METHODS: Nine metabolic proteins were identified in a siRNA-based screen, with phosphomannose mutase 2 (PMM2) showing the most promise. We measured the impact of PMM2 depletion on ERα stability and cell proliferation in ERα Y537S mutant cells. Additionally, we tested the effect of PMM2 reduction on the hyperactive phenotype of the mutant and its proliferation when combined with metastatic BC treatment drugs. RESULTS: PMM2 emerged as a significant target due to its correlation with better relapse-free survival, overexpression in ERα-positive tumors, and its elevation in ERα Y537S-expressing cells. Depletion of PMM2 induces degradation of ERα Y537S, inhibits cell proliferation, and reduces ERα signaling. Notably, reducing PMM2 levels re-sensitizes ERα Y537S-expressing cells to certain ET drugs and CDK4/CDK6 inhibitors. Mechanistically, depletion of PMM2 leads to a reduction in ESR1 mRNA levels, resulting in decreased ERα receptor protein expression. Furthermore, the reduction of PMM2 decreases FOXA1 levels, which plays a crucial role in ERα regulation. CONCLUSIONS: Our findings establish PMM2 as an innovative therapeutic target for metastatic BC expressing the ERα Y537S variant, offering alternative strategies for managing and treating this disease.

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PURPOSE: In the absence of prospective data on neurological symptoms, disease outcome, or guidelines for system specific management in phosphomannomutase 2-congenital disorders of glycosylation (PMM2-CDG), we aimed to collect and review natural history data. METHODS: Fifty-one molecularly confirmed individuals with PMM2-CDG enrolled in the Frontiers of Congenital Disorders of Glycosylation natural history study were reviewed. In addition, we prospectively reviewed a smaller cohort of these individuals with PMM2-CDG on off-label acetazolamide treatment. RESULTS: Mean age at diagnosis was 28.04 months. Developmental delay is a constant phenotype. Neurological manifestation included ataxia (90.2%), myopathy (82.4%), seizures (56.9%), neuropathy (52.9%), microcephaly (19.1%), extrapyramidal symptoms (27.5%), stroke-like episodes (SLE) (15.7%), and spasticity (13.7%). Progressive cerebellar atrophy is the characteristic neuroimaging finding. Additionally, supratentorial white matter changes were noted in adult age. No correlation was observed between the seizure severity and SLE risk, although all patients with SLE have had seizures in the past. "Off-label" acetazolamide therapy in a smaller sub-cohort resulted in improvement in speech fluency but did not show statistically significant improvement in objective ataxia scores. CONCLUSION: Clinical and radiological findings suggest both neurodevelopmental and neurodegenerative pathophysiology. Seizures may manifest at any age and are responsive to levetiracetam monotherapy in most cases. Febrile seizure is the most common trigger for SLEs. Acetazolamide is well tolerated.

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INTRODUCTION: The study of protein stability is crucial to biochemistry and relies on different methodologies. Recently, the Cellular Thermal Shift Assay has been introduced to study protein stability in whole cells. METHODS: We report a novel application of CeTSA named ReBaTSA. This Recombinant Bacterial TSA was performed using clear extracts from bacteria expressing a recombinant protein, incubated at different temperatures, centrifuged and analyzed via SDS-PAGE. RESULTS AND CONCLUSIONS: We demonstrated the feasibility and reliability of this simplified approach. We validated the method using the protein phosphomannomutase-2 and its common mutants, which were compared in the presence or the absence of a known ligand.

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PURPOSE: Congenital disorders of glycosylation (CDG) are one of the fastest growing groups of inborn errors of metabolism. Despite the availability of next-generation sequencing techniques and advanced methods for evaluation of glycosylation, CDG screening mainly relies on the analysis of serum transferrin (Tf) by isoelectric focusing, HPLC or capillary electrophoresis. The main pitfall of this screening method is the presence of Tf protein variants within the general population. Although reports describe the role of Tf variants leading to falsely abnormal results, their significance in confounding diagnosis in patients with CDG has not been documented so far. Here, we describe two PMM2-CDG cases, in which Tf variants complicated the diagnostic. EXPERIMENTAL DESIGN: Glycosylation investigations included classical screening techniques (capillary electrophoresis, isoelectric focusing and HPLC of Tf) and various confirmation techniques (two-dimensional electrophoresis, western blot, N-glycome, UPLC-FLR/QTOF MS with Rapifluor). Tf variants were highlighted following neuraminidase treatment. Sequencing of PMM2 was performed. RESULTS: In both patients, Tf screening pointed to CDG-II, while second-line analyses pointed to CDG-I. Tf variants were found in both patients, explaining these discrepancies. PMM2 causative variants were identified in both patients. CONCLUSION AND CLINICAL RELEVANCE: We suggest that a neuraminidase treatment should be performed when a typical CDG Tf pattern is found upon initial screening analysis.

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Inherited deficiency of phosphomannomutase 2 (PMM2) (aka PMM2-CDG) is the most common congenital disorders of glycosylation (CDG) and has no cure. With debilitating morbidity and significant mortality, it is imperative to explore novel, safe, and effective therapies for the disease. Our Proof-of-Concept study showed that AAV9-PMM2 infection of patient fibroblasts augmented PMM2 expression and improved glycosylation. Thus, AAV9-PMM2 gene replacement is a promising therapeutic strategy for PMM2-CDG patients.

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Algal-bacterial membrane photobioreactor (AMPBR) is proven as a highly energy-efficient process for treating domestic wastewater. This study compared the application of polymeric micro-membrane (PMM) and a low-cost ceramic membrane (LCM) to the AMPBR process for treating domestic wastewater with low and high organic pollution levels. Experiments were conducted over 57 days using two PMM-AMPBRs and two LCM-AMPBRs, operating on a 12-h dark/light cycle in a continuous mode. Simulated wastewater containing varying levels of chemical oxygen demand (COD) was fed to reactors for a consistent hydraulic residence time (HRT) of 7 d and a flux rate of 100 L/m2/d. PMM and LCM-AMPBRs demonstrated efficient wastewater treatment capabilities, achieving COD removal rates exceeding 94% and 95% for high and low COD loadings, respectively. PMM-AMPBR achieved 54.1% TN removal at low COD loading, while LCM-AMPBR achieved 57.2%. These removal efficiencies decreased to 45.6% and 47.0% under high COD loading. Total Phosphorus (TP) removal reached 29-33% for PMM-AMPBRs and 21-24% for LCM-AMPBRs, irrespective of COD loading. LCM-AMPBRs showed significantly lower fouling frequency than PMM-AMPBRs. The biomass production rate decreased with increasing COD loading and achieved 40 mg/L/d at low COD loading for both AMPBRs. Net energy return (NER) values for both AMPBRs were close to 0.87, indicating them as energy-efficient processes. Considering the cost-effectiveness and comparable performance, LCM-AMPBR could be a viable alternative to PMM-AMPBR for wastewater treatment, particularly under low COD loading conditions.

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Although thrombocytopenia in neonatal intensive care patients is rarely due to inherited disorders, the number of genetic variants implicated in platelet defects has grown dramatically with increasing genome-wide sequencing. Here we describe a case of severe, oligogenic neonatal thrombocytopenia and reinterpret a reportedly benign mutation that is likely pathogenic. Despite this patient's synonymous mutation (GFI1B 576 C>T, Phe192=) being annotated as benign, GFI1B is a well-known regulator of megakaryopoiesis, this variant alters splicing and megakaryocyte maturation, and our analysis of existing genome-wide associated studies demonstrates that it likely causes gray platelet syndrome. This variant has not been reported in a case of life-threatening thrombocytopenia. We propose that the severity of this patient's phenotype is due to synergistic epistasis between the intrinsic platelet defect caused by this mutation and her concomitant inherited PMM2 congenital glycosylation disorder neither of which have been associated with such a severe phenotype. This case highlights the importance of whole-exome/genome sequencing for critically ill patients, reexamining variant interpretation when clinically indicated, and the need to study diverse genetic variation in hematopoiesis.

What is the context? Low platelets (thrombocytopenia) in the neonatal population is not frequently inherited. As we perform unbiased DNA sequencing in more patients, the number of inherited platelet disorders and implicated variants is growing.The gene GFI1B encodes for a transcription factor that regulates megakaryocytes, the cell type that produces platelets. A synonymous substitution in GFI1B (576 C>T, Phe192=) is annotated as benign; however, experimental studies have shown that it inhibits megakaryocyte production.There is growing appreciation for oligogenic inheritance, where multiple causal variants contribute to clinical phenotypes.What is new? We present a case of life-threatening neonatal macrothrombocytopenia (large, hypogranulated sparse platelets) that has an oligogenic cause. We reinterpret the synonymous substitution GFI1B 576 C>T as pathogenic.This patient's severe phenotype was likely due to the combined effect of GFI1B 576 C>T and her inherited glycosylation disorder (PMM2-CDG). Neither variant alone causes severe thrombocytopenia, but the combined intrinsic platelet defect (GFI1B mutation) and consumption (PMM2-CDG) likely produced her life-threatening phenotype.What is the impact? GFI1B is a critical regulator of megakaryocyte production. The purportedly benign mutation 576 C>T is likely pathogenic causing thrombocytopenia by impairing megakaryocyte maturation.As more patients have unbiased genome sequencing, oligogenic and polygenic inheritance will become increasingly appreciated as causes of platelet disorders.NICU providers should consider whole genome or exome sequencing of neonates with severe thrombocytopenia after reversible causes are ruled out.

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We report a patient with an extremely rare, combined diagnosis of PMM2-CDG and hereditary fructose intolerance (HFI). By comparing with other patients, under-galactosylation was identified as a feature of HFI. Fructose/sorbitol/sucrose restriction was initiated right afterwards. The patient is at the mild end of the PMM2-CDG spectrum, raising the question of sorbitol's role in the pathogenesis of PMM2-CDG and whether fructose/sorbitol/sucrose restriction could benefit other PMM2-CDG patients. Additionally, epalrestat, an emerging potential PMM2-CDG therapy, may benefit HFI patients.

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