Neurological manifestations in PMM2-congenital disorders of glycosylation (PMM2-CDG): Insights into clinico-radiological characteristics, recommendations for follow-up, and future directions.

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.

Liposome-encapsulated mannose-1-phosphate therapy improves global N-glycosylation in different congenital disorders of glycosylation.

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.

Sensitivity of transferrin isoform analysis for PMM2-CDG.

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.

HepG2 PMM2-CDG knockout model: A versatile platform for variant and therapeutic evaluation.

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.

Motor improvement in children with PMM2-CDG syndrome following a six-month rehabilitation treatment utilising whole-body vibration; a retrospective study.

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.

Association between acute complications in PMM2-CDG patients and haemostasis anomalies: Data from a multicentric study and suggestions for acute management.

OBJECTIVES: Patients with PMM2-CDG develop acute events (stroke-like episodes (SLEs), thromboses, haemorrhages, seizures, migraines) associated with both clotting factors (factor XI) and coagulation inhibitors (antithrombin, protein C and protein S) deficiencies. The aim of the study was to correlate acute events to haemostasis and propose practical guidelines. METHODS: In this multicentric retrospective study, we evaluated clinical, radiological, haemostasis and electroencephalography data for PMM2-CDG patients hospitalized for acute events. Cerebral events were classified as thrombosis, haemorrhage, SLE, or "stroke mimic" (SM: normal brain imaging or evoking a migraine). RESULTS: Thirteen patients had a total of 31 acute episodes: 27 cerebral events with 7 SLEs, 4 venous thromboses, 4 haemorrhages (3 associated with thrombosis), 15 SMs at a mean age of 7.7 years; 4 non-cerebral thromboses, one of which included bleeding. A trigger was frequently involved (infection, head trauma). Although sometimes normal at baseline state, factor XI, antithrombin and protein C levels decreased during these episodes. No correlation between haemostasis anomalies and type of acute event was found. DISCUSSION: Acute events in PMM2-CDG are not negligible and are associated with haemostasis anomalies. An emergency protocol is proposed for their prevention and treatment (https://www.filiere-g2m.fr/urgences). For cerebral events, brain Magnetic Resonance Imaging with perfusion weight imaging and diffusion sequences, electroencephalogram and haemostasis protein levels guide the treatment: anticoagulation, antithrombin or fresh frozen plasma supplementation, antiepileptic therapy. Preventing bleeding and thrombosis is required in cases of surgery, prolonged immobilization, hormone replacement therapy. CONCLUSION: Acute events in PMM2-CDG are associated with abnormal haemostasis, requiring practical guidance.

Metabolic adaptation of human skin fibroblasts to ER stress caused by glycosylation defect in PMM2-CDG.

PMM2-CDG is the most prevalent type of congenital disorders of glycosylation (CDG). It is caused by pathogenic variants in the gene encoding phosphomannomutase 2 (PMM2), which converts mannose-6-phosphate to mannose-1-phosphate and thus activates this saccharide for further glycosylation processes. Defective glycosylation can lead to an abnormal accumulation of unfolded proteins in endoplasmic reticulum (ER) and cause its stress. The ER is a key compartment for glycosylation, and its connection and communication with mitochondria has been described extensively in literature. Their crosstalk is important for cell proliferation, calcium homeostasis, apoptosis, mitochondrial fission regulation, bioenergetics, autophagy, lipid metabolism, inflammasome formation and unfolded protein response. Therefore, in the present study we posed a question, whether defective glycosylation leads to bioenergetic disruption. Our data reveal possible chronic stress in ER and activated unfolded protein response via PERK pathway in PMM2-CDG fibroblasts. Presumably, it leads to bioenergetic reorganization and increased assembly of respiratory chain complexes into supercomplexes together with suppressed glycolysis in PMM2-CDG patient cells. These changes cause alterations in Krebs cycle, which is tightly connected to electron transport system in mitochondria. In summary, we present data showing metabolic adaptation of cells to glycosylation defect caused by various pathogenic variants in PMM2.

Complex metabolic disharmony in PMM2-CDG paves the way to new therapeutic approaches.

PMM2-CDG is the most common defect among the congenital disorders of glycosylation. In order to investigate the effect of hypoglycosylation on important cellular pathways, we performed extensive biochemical studies on skin fibroblasts of PMM2-CDG patients. Among others, acylcarnitines, amino acids, lysosomal proteins, organic acids and lipids were measured, which all revealed significant abnormalities. There was an increased expression of acylcarnitines and amino acids associated with increased amounts of calnexin, calreticulin and protein-disulfid-isomerase in combination with intensified amounts of ubiquitinylated proteins. Lysosomal enzyme activities were widely decreased as well as citrate and pyruvate levels indicating mitochondrial dysfunction. Main lipid classes such as phosphatidylethanolamine, cholesterol or alkyl-phosphatidylcholine, as well as minor lipid species like hexosylceramide, lysophosphatidylcholines or phosphatidylglycerol, were abnormal. Biotinidase and catalase activities were severely reduced. In this study we discuss the impact of metabolite abnormalities on the phenotype of PMM2-CDG. In addition, based on our data we propose new and easy-to-implement therapeutic approaches for PMM2-CDG patients.

Liver transplantation recovers hepatic N-glycosylation with persistent IgG glycosylation abnormalities: Three-year follow-up in a patient with phosphomannomutase-2-congenital disorder of glycosylation.

Phosphomannomutase-2-congenital disorder of glycosylation (PMM2-CDG) is the most common CDG and presents with highly variable features ranging from isolated neurologic involvement to severe multi-organ dysfunction. Liver abnormalities occur in in almost all patients and frequently include hepatomegaly and elevated aminotransferases, although only a minority of patients develop progressive hepatic fibrosis and liver failure. No curative therapies are currently available for PMM2-CDG, although investigation into several novel therapies is ongoing. We report the first successful liver transplantation in a 4-year-old patient with PMM2-CDG. Over a 3-year follow-up period, she demonstrated improved growth and neurocognitive development and complete normalization of liver enzymes, coagulation parameters, and carbohydrate-deficient transferrin profile, but persistently abnormal IgG glycosylation and recurrent upper airway infections that did not require hospitalization. Liver transplant should be considered as a treatment option for PMM2-CDG patients with end-stage liver disease, however these patients may be at increased risk for recurrent bacterial infections post-transplant.

Combined PMM2-CDG and hereditary fructose intolerance in a patient with mild clinical presentation.

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.

A functional platform for the selection of pathogenic variants of PMM2 amenable to rescue via the use of pharmacological chaperones.

Different strategies are being investigated for treating PMM2-CDG, the most common congenital disorder of glycosylation. The use of pharmacochaperones (PCs) is one of the most promising. The present work characterizes the expression, stability, and enzymatic properties of 15 previously described clinical variants of the PMM2 protein, four novel variants, the Pmm2 mouse variant p.Phe115Leu, and its p.Phe119Leu human counterpart, with the aim of extending the potential use of pharmacochaperoning treatment. PMM2 variants were purified as stable homodimers, except for p.Asp65Gly, p.Ile120Thr, and p.Thr237Lys (no expression detected), p.Thr226Ser and p.Val231Met (aggregates), and p.Glu93Ala, p.Phe119Leu, and p.Phe115Leu (partial dissociated). Enzyme activity analyses identified severe variants and milder ones. Pure dimeric mutant proteins showed a reduction in thermal stability except for p.Asn216Asp. The thermal stability of all the unstable mutants was recovered in the presence of the PC compound VIII. This study adds to the list of destabilizing human variants amenable to rescue by small chemical compounds that increase the stability/activity of PMM2. The proposed platform can be reliably used for assessing the disease-causing effects of PMM2 missense variants, for assessing the correlation between genotype and phenotype, for confirming new clinical defects, and for identifying destabilizing mutations amenable to rescue by PCs.

Dissecting the transcriptional program of phosphomannomutase 2-deficient cells: Lymphoblastoide B cell lines as a valuable model for congenital disorders of glycosylation studies.

Congenital disorders of glycosylation (CDG) include 150 genetically and clinically heterogeneous diseases, showing significant glycoprotein hypoglycosylation that leads to pathological consequences in multiple organs and systems whose underlying mechanisms are not yet understood. A few cellular and animal models have been used to study specific CDG characteristics, although they have given limited information due to the few CDG mutations tested and the still missing comprehensive molecular and cellular basic research. Here, we provide specific gene expression profiles, based on ribonucleic acid (RNA) microarray analysis, together with some biochemical and cellular characteristics of a total of nine control Epstein-Barr virus-transformed lymphoblastoid B cell lines (B-LCL) and 13 CDG B-LCL from patients carrying severe mutations in the phosphomannomutase 2 (PMM2) gene, strong serum protein hypoglycosylation and neurological symptoms. Significantly dysregulated genes in PMM2-CDG cells included those regulating stress responses, transcription factors, glycosylation, motility, cell junction and, importantly, those related to development and neuronal differentiation and synapse, such as carbonic anhydrase 2 (CA2) and ADAM23. PMM2-CDG-associated biological consequences involved the unfolded protein response, RNA metabolism and the endoplasmic reticulum, Golgi apparatus and mitochondria components. Changes in the transcriptional and CA2 protein levels are consistent with the CDG physiopathology. These results demonstrate the global transcriptional impact in phosphomannomutase 2-deficient cells, reveal CA2 as a potential cellular biomarker and confirm B-LCL as an advantageous model for CDG studies.

Patient-reported outcomes and quality of life in PMM2-CDG.

Patient-reported outcomes (PROs) measure important aspects of disease burden, however they have received limited attention in the care of patients with Congenital Disorders of Glycosylation (CDG). We evaluated the PROs and correlation between clinical disease severity scoring and reported quality of life (QoL) in a PMM2-CDG patient cohort. Twenty-five patients with diagnosis of PMM2-CDG were enrolled as part of the Frontiers in Congenital Disorders of Glycosylation Consortium (FCDGC) natural history study. Patient- Reported Outcomes Measurement Information System (PROMIS) was completed by caregivers to assess health-related QoL. Clinical disease severity was scored by medical providers using the Nijmegen Progression CDG Rating Scale (NPCRS). The domains such as physical activity, strength impact, upper extremity, physical mobility, and a satisfaction in social roles (peer relationships) were found to be the most affected in the PMM2-CDG population compared to US general population. We found a strong correlation between NPCRS 1 (current functional ability) and three out of ten PROMIS subscales. NPCRS 2 (laboratory and organ function) and NPCRS 3 (neurological involvement) did not correlate with PROMIS. Mental health domains, such as anxiety, were positively correlated with depressive symptoms (r = 0.76, p = 0.004), fatigue (r = 0.67, p = 0.04). Surprisingly, patients with severely affected physical mobility showed low anxiety scores according to PROMIS (inverse correlation, r = -0.74, p = 0.005). Additionally, there was a positive correlation between upper extremity and physical mobility (r = 0.75, p = 002). Here, we found that PROMIS is an informative additional tool to measure CDG disease burden, which could be used as clinical trial outcome measures. The addition of PROMIS to clinical follow-up could help improve the quality of care for PMM2-CDG by facilitating a holistic approach for clinical decision-making. SYNOPSIS: We recommend PROMIS as an informative tool to measure disease burden in PMM2-CDG in addition to traditional CDG disease severity scores.

Insight on molecular pathogenesis and pharmacochaperoning potential in phosphomannomutase 2 deficiency, provided by novel human phosphomannomutase 2 structures.

Phosphomannomutase 2 (PMM2) deficiency, the most frequent congenital disorder of glycosylation (PMM2-CDG), is a severe condition, which has no cure. Due to the identification of destabilizing mutations, our group aims at increasing residual activity in PMM2-CDG patients, searching for pharmacochaperones. Detailed structural knowledge of hPMM2 might help identify variants amenable to pharmacochaperoning. hPMM2 structural information is limited to one incomplete structure deposited in the Protein Databank without associated publication, which lacked ligands and residues from a crucial loop. Here we report five complete crystal structures of hPMM2, three for wild-type and two for the p.Thr237Met variant frequently found among Spanish PMM2-CDG patients, free and bound to the essential activator glucose-1,6-bisphosphate (Glc-1,6-P2 ). In the hPMM2 homodimer, each subunit has a different conformation, reflecting movement of the distal core domain relative to the dimerization cap domain, supporting an opening/closing process during catalysis. Two Mg2+ ions bind to the core domain, one catalytic and one structural. In the cap domain, the site for Glc-1,6-P2 is well delineated, while a Cl- ion binding at the intersubunit interface is predicted to strengthen dimerization. Patient-found amino acid substitutions are nonhomogeneously distributed throughout hPMM2, reflecting differential functional or structural importance for various parts of the protein. We classify 93 of 101 patient-reported single amino acid variants according to five potential pathogenetic mechanism affecting folding of the core and cap domains, linker 2 flexibility, dimerization, activator binding, and catalysis. We propose that ~80% and ~50% of the respective core and cap domains substitutions are potential candidates for pharmacochaperoning treatment.

Should patients with Phosphomannomutase 2-CDG (PMM2-CDG) be screened for adrenal insufficiency?

PMM2-CDG is the most common congenital disorder of glycosylation (CDG) accounting for almost 65% of known CDG cases affecting N-glycosylation. Abnormalities in N-glycosylation could have a negative impact on many endocrine axes. There is very little known on the effect of impaired N-glycosylation on the hypothalamic-pituitary-adrenal axis function and whether CDG patients are at risk of secondary adrenal insufficiency and decreased adrenal cortisol production. Cortisol and ACTH concentrations were simultaneously measured between 7:44 am to 1 pm in forty-three subjects (20 female, median age 12.8 years, range 0.1 to 48.6 years) participating in an ongoing international, multi-center Natural History study for PMM2-CDG (ClinicalTrials.gov Identifier: NCT03173300). Of the 43 subjects, 11 (25.6%) had cortisol below 5 µg/dl and low to normal ACTH levels, suggestive of secondary adrenal insufficiency. Two of the 11 subjects have confirmed central adrenal insufficiency and are on hydrocortisone replacement and/or stress dosing during illness; 3 had normal and 1 had subnormal cortisol response to ACTH low-dose stimulation test but has not yet been started on therapy; the remaining 5 have upcoming stimulation testing planned. Our findings suggest that patients with PMM2-CDG may be at risk for adrenal insufficiency. Monitoring of morning cortisol and ACTH levels should be part of the standard care in patients with PMM2-CDG.

Nrf2 activation attenuates genetic endoplasmic reticulum stress induced by a mutation in the phosphomannomutase 2 gene in zebrafish.

Nrf2 plays critical roles in animals' defense against electrophiles and oxidative stress by orchestrating the induction of cytoprotective genes. We previously isolated the zebrafish mutant it768, which displays up-regulated expression of Nrf2 target genes in an uninduced state. In this paper, we determine that the gene responsible for it768 was the zebrafish homolog of phosphomannomutase 2 (Pmm2), which is a key enzyme in the initial steps of N-glycosylation, and its mutation in humans leads to PMM2-CDG (congenital disorders of glycosylation), the most frequent type of CDG. The pmm2it768 larvae exhibited mild defects in N-glycosylation, indicating that the pmm2it768 mutation is a hypomorph, as in human PMM2-CDG patients. A gene expression analysis showed that pmm2it768 larvae display up-regulation of endoplasmic reticulum (ER) stress, suggesting that the activation of Nrf2 was induced by the ER stress. Indeed, the treatment with the ER stress-inducing compounds up-regulated the gstp1 expression in an Nrf2-dependent manner. Furthermore, the up-regulation of gstp1 by the pmm2 inactivation was diminished by knocking down or out double-stranded RNA-activated protein kinase (PKR)-like ER kinase (PERK), one of the main ER stress sensors, suggesting that Nrf2 was activated in response to the ER stress via the PERK pathway. ER stress-induced activation of Nrf2 was reported previously, but the results have been controversial. Our present study clearly demonstrated that ER stress can indeed activate Nrf2 and this regulation is evolutionarily conserved among vertebrates. Moreover, ER stress induced in pmm2it768 mutants was ameliorated by the treatment of the Nrf2-activator sulforaphane, indicating that Nrf2 plays significant roles in the reduction of ER stress.

Genotypes and estimated prevalence of phosphomannomutase 2 deficiency in Turkey differ significantly from those in Europe.

Phosphomannomutase 2 deficiency (PMM2-CDG) is an autosomal recessive congenital disorder of glycosylation, characterized by multisystem phenotypes, mostly including neurological involvement. In Turkey, due to high rates of consanguinity, many patients with autosomal recessive disorders have homozygous variants and these diseases are more common, compared to Europe. However, published reports of PMM2-CDG from Turkey are scarce. Here, we describe clinical and molecular characteristics of PMM2-CDG patients diagnosed in three centers in Turkey, using data obtained retrospectively from hospital records. We also analyzed an in-house exome database of 1,313 individuals for PMM2 variants and estimated allele, carrier and disease frequencies, using the Hardy-Weinberg law. Eleven patients were identified from 10 families, displaying similar characteristics to previous publications, with the exception of the first report of epilepsia partialis continua and increased prevalence of sensorineural hearing loss. p.Val231Met was the most common variant, and was homozygous in four patients. This novel genotype results in a neurological phenotype with subclinical visceral involvement. Exome database analysis showed an estimated prevalence of 1:286,726 for PMM2-CDG, which is much lower than expected (1:20,000 in Europe) because of the lack of predominance of the common European p.Asp141His allele, associated with a severe phenotype (allele frequency of 1:2,622 compared to 1:252 in gnomAD). These data suggest that prevalence, phenotypes and genotypes of PMM2-CDG in Turkey differ significantly from those in Europe: Milder phenotypes may be more common, but the disease itself rarer, requiring a higher clinical suspicion for diagnosis. The association of sensorineural hearing loss with PMM2-CDG warrants further study.

Long-term follow-up in PMM2-CDG: are we ready to start treatment trials?

PURPOSE: PMM2-CDG is the most common congenital disorder of glycosylation (CDG), which presents with either a neurologic or multisystem phenotype. Little is known about the longitudinal evolution. METHODS: We performed data analysis on PMM2-CDG patients' clinical features according to the Nijmegen CDG severity score and laboratory data. Seventy-five patients (28 males) were followed up from 11.0 ± 6.91 years for an average of 7.4 ± 4.5 years. RESULTS: On a group level, there was no significant evolution in overall clinical severity. There was some improvement in mobility and communication, liver and endocrine function, and strabismus and eye movements. Educational achievement and thyroid function worsened in some patients. Overall, the current clinical function, the system-specific involvement, and the current clinical assessment remained unchanged. On follow-up there was improvement of biochemical variables with (near) normalization of activated partial thromboplastin time (aPTT), factor XI, protein C, antithrombin, thyroid stimulating hormone, and liver transaminases. CONCLUSION: PMM2-CDG patients show a spontaneous biochemical improvement and stable clinical course based on the Nijmegen CDG severity score. This information is crucial for the definition of endpoints in clinical trials.

Clinical and whole-exome sequencing findings in two siblings from Hani ethnic minority with congenital glycosylation disorders.

BACKGROUND: PMM2-CDG, is the most common N-linked glycosylation disorder and subtype among all CDG syndromes, which are a series of genetic disorders involving the synthesis and attachment of glycoproteins and glycolipid glycans. The mutations of PMM2-CDG might lead to the loss of PMM2, which is responsible for the conversion of mannose 6- phosphate into mannose 1-phosphate. Most patients with PMM2-CDG have central nervous system involvement, abnormal coagulation, and hepatopathy. The neurological symptoms of PMM2-CDG are intellectual disability (ID), cerebellar ataxia, and peripheral neuropathy. Now, over 100 new CDG cases have been reported. However, each type of CDG is very rare, and CDGs are problematic to diagnose. In addition, few CDGs have been reported in the Chinese population. CASE PRESENTATION: Here we present a Hani ethnic minority family including two siblings with congenital glycosylation disorders. Whole-exome sequencing revealed compound heterozygous for one novel mutation (c.241-242 del variant) and previously reported mutation (c.395 T > C) in gene of PMM2. Two mutations were found in proband and her sibling by whole-exome sequencing. The mutations were identified in this family by Sanger sequencing and no mutations were detected in the normal control. CONCLUSIONS: This is the first report to describe mutations in two siblings of Hani ethnic minority which is one of five ethnic groups found only in Yunnan with a population of more than 1 million.

Clinical and molecular diagnosis of non-phosphomannomutase 2 N-linked congenital disorders of glycosylation in Spain.

The congenital disorders of glycosylation (CDG) are defects in glycoprotein and glycolipid glycan synthesis and attachment. They affect multiple organ/systems, but non-specific symptoms render the diagnosis of the different CDG very challenging. Phosphomannomutase 2 (PMM2)-CDG is the most common CDG, but advances in genetic analysis have shown others to occur more commonly than previously thought. The present work reports the clinical and mutational spectrum of 25 non-PMM2 CDG patients. The most common clinical symptoms were hypotonia (80%), motor or psychomotor disability (80%) and craniofacial dysmorphism (76%). Based on their serum transferrin isoform profile, 18 were classified as CDG-I and 7 as CDG-II. Pathogenic variations were found in 16 genes (ALG1, ALG6, ATP6V0A2, B4GALT1, CCDC115, COG7, DOLK, DPAGT1, DPM1, GFPT1, MPI, PGM1, RFT1, SLC35A2, SRD5A3, and SSR4). Overall, 27 variants were identified, 12 of which are novel. The results highlight the importance of combining genetic and biochemical analyses for the early diagnosis of this heterogeneous group of disorders.