Clinical, biochemical and molecular phenotype of congenital disorders of glycosylation: long-term follow-up

Identification of a novel intronic variant of ATP6V0A2 in a Han-Chinese family with cutis laxa

BACKGROUND

Cutis laxa is a connective tissue disease caused by abnormal synthesis or secretion of skin elastic fibers, leading to skin flabby and saggy in various body parts. It can be divided into congenital cutis laxa and acquired cutis laxa, and inherited cutis laxa syndromes is more common in clinic.

METHODS

In this study, we reported a case of a Han-Chinese male newborn with ATP6V0A2 gene variant leading to cutis laxa. The proband was identified by whole-exome sequencing to determine the novel variant, and their parents were verified by Sanger sequencing. Bioinformatics analysis and minigene assay were used to verify the effect of this variant on splicing function.

RESULTS

The main manifestations of the proband are skin laxity, abnormal facial features, and enlargement of the anterior fontanelle. Whole-exome sequencing showed that the newborn carried a non-canonical splicing-site variant c.117 + 5G > T, p. (?) in ATP6V0A2 gene. Sanger sequencing showed that both parents of the proband carried the heterozygous variant. The results of bioinformatics analysis and minigene assay displayed that the variant site affected the splicing function of pre-mRNA of the ATP6V0A2 gene.

CONCLUSIONS

In this study, it was identified that ATP6V0A2 gene c. 117 + 5G > T may be the cause of the disease. The non-canonical splicing variants of ATP6V0A2 gene were rarely reported in the past, and this variant expanded the variants spectrum of the gene. The functional study of minigene assay plays a certain role in improving the level of evidence for the pathogenicity of splicing variants, which lays a foundation for prenatal counseling and follow-up gene therapy.

Revisiting the immunopathology of congenital disorders of glycosylation: an updated review

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.

Dysregulated proteome and N-glycoproteome in ALG1-deficient fibroblasts

Asparagine-linked glycosylation 1 protein is a β-1,4-mannosyltransferase, is encoded by the ALG1 gene, which catalyzes the first step of mannosylation in N-glycosylation. Pathogenic variants in ALG1 cause a rare autosomal recessive disorder termed as ALG1-CDG. We performed a quantitative proteomics and N-glycoproteomics study in fibroblasts derived from patients with one homozygous and two compound heterozygous pathogenic variants in ALG1. Several proteins that exhibited significant upregulation included insulin-like growth factor II and pleckstrin, whereas hyaluronan and proteoglycan link protein 1 was downregulated. These proteins are crucial for cell growth, survival and differentiation. Additionally, we observed a decrease in the expression of mitochondrial proteins and an increase in autophagy-related proteins, suggesting mitochondrial and cellular stress. N-glycoproteomics revealed the reduction in high-mannose and complex/hybrid glycopeptides derived from numerous proteins in patients explaining that defect in ALG1 has broad effects on glycosylation. Further, we detected an increase in several short oligosaccharides, including chitobiose (HexNAc2 ) trisaccharides (Hex-HexNAc2 ) and novel tetrasaccharides (NeuAc-Hex-HexNAc2 ) derived from essential proteins including LAMP1, CD44 and integrin. These changes in glycosylation were observed in all patients irrespective of their gene variants. Overall, our findings not only provide novel molecular insights into understanding ALG1-CDG but also offer short oligosaccharide-bearing peptides as potential biomarkers.

Compound heterozygous variants in MAN2B2 identified in a Chinese child with congenital disorders of glycosylation

Congenital disorders of glycosylation (CDG) is a group inherited disorders. It is characterized by multi-organ dysfunction with significant morbidity and mortality. MAN2B2-CDG caused by pathogenic variants in the MAN2B2 gene was a rare CDG. To date, only one case of MAN2B2-CDG was reported. The representative clinical features were immune deficiency, dysmorphic facial features, coagulopathy, and severe developmental delay. More cases are needed to support the pathogenesis of MAN2B2 variation and elucidate its clinical heterogeneity. In this study, we described the clinical presentations of a CDG proband with compound heterozygous variants in MAN2B2. Serum N-glycan profiling was measured by MALDI coupled to time-of-flight mass spectrometry (MALDI-TOF MS). MALDI-TOF MS analysis of patient serum showed disorders of N-linked glycosylation, including increased N-glycans and elevated Man5/Man6 and Man5/Man9 value. Our proband presented severe developmental delay, dysmorphic facial features as in the previous case. But our case presented new features, including cleft palate and hypospadias with no immune deficiency. Our data expands both the molecular and clinical phenotypes of MAN2B2-CDG and highlights the importance of the role of MAN2B2 gene in CDG.

A novel variant in ALG1 gene associated with congenital disorder of glycosylation: A case report and short literature review

BACKGROUND

The congenital disorder of glycosylation associated with ALG1 (ALG1-CDG) is a rare autosomal recessive disease. Due to the deficiency of β1,4 mannosyltransferase caused by pathogenic variants in ALG1 gene, the assembly and processing of glycans in the protein glycosylation pathway are impaired, resulting in a broad clinical spectrum with multi-organ involvement. To raise awareness of clinicians for its manifestations and genotype, we here reported a new patient with a novel variant in ALG1 gene and reviewed the literature to study the genotype-phenotype correlation.

METHOD

Clinical characteristics were collected, and clinical exome sequencing was used to identify the causative variants. MutationTaster, PyMol, and FoldX were used to predict the pathogenicity, changes in 3D model molecular structure of protein, and changes of free energy caused by novel variants.

RESULTS

The proband was a 13-month-old Chinese Han male characterized by epileptic seizures, psychomotor development delay, muscular hypotonia, liver and cardiac involvement. Clinical exome sequencing revealed the biallelic compound heterozygosity variants, a previously reported variant c.434G>A (p.G145N, paternal) and a novel variant c.314T>A (p.V105N, maternal). The literature review found that in severe phenotypes, the incidences of clinical manifestations were significantly higher than that in mild phenotypes, including congenital nephrotic syndrome, agammaglobulinemia, and severe hydrops. Homozygous c.773C>T was a strongly pathogenic variant associated with a severe phenotype. When heterozygous for c.773C>T, patients with another variant leading to substitution in amino acids within the strongly conserved regions (c.866A>T, c.1025A>C, c.1182C>G) may cause a more severe phenotype than those within less-conserved regions (c.434G>A, c.450C>G, c.765G>A, c.1287T>A). c.1129A>G, c.1076C>T, and c.1287T>A were more likely to be associated with a mild phenotype. The assessment of disease phenotypes requires a combination of genotype and clinical manifestations.

CONCLUSIONS

The case reported herein adds to the mutations identified in ALG1-CDG and a review of this literature expands the study of the phenotypic and genotypic spectrum of this disorder.

Phylogenetic analysis of promoter regions of human Dolichol kinase (DOLK) and orthologous genes using bioinformatics tools

The Dolichol kinase (DOLK) gene encodes the polytopic DOLK protein associated with the endoplasmic reticulum (ER) N-glycosylation pathway catalyzing the final step in the biosynthesis of dolichol phosphate. Dolichol phosphate is an oligosaccharide carrier required for N-glycosylation of DOLK protein, with its deficiency leading to a severe hypo glycosylation phenotype in humans which can cause congenital disorders of glycosylation and death in early infancy. The aim of the present study is to identify the phylogenetic relationship between human and ortholog species based on their conserved sequences in DOLK gene. Sequence alignment of DOLK was carried out in this study and the evolutionarily conserved regulatory sequences were identified using bioinformatics. Promoter sequence of human DOLK was compared with orthologous sequences from different organisms. Conserved non-coding sequences (CNS) and motifs in promoter regions were found by analyzing upstream promoter sequences of Homo sapiens DOLK and its orthologous genes in other organisms. Conserved sequences were predicted in the promoter regions in CNS1 and CNS2. Conserved protein sequences were also identified by alignment of the orthologous sequences. Organisms with similar gene sequences are assumed to be closely related and the ER N-glycosylation pathway is conserved in them.

Metabolic Cardiomyopathies and Cardiac Defects in Inherited Disorders of Carbohydrate Metabolism: A Systematic Review

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

Unique clinical presentations and follow-up outcomes from experience with congenital disorders of glycosylation: PMM2-PGM1-DPAGT1-MPI-POMT2-B3GALNT2-DPM1-SRD5A3-CDG

OBJECTIVES

Congenital Glycosylation Disorders (CDG) are a large group of inherited metabolic diseases with multi-organ involvement. Herein, we aimed to expand the clinical characteristics of patients with CDG based on our experience with diagnoses and follow-up of CDG patients from different subtypes.

METHODS

The clinical and laboratory findings from the last 15 years were reviewed retrospectively in Ege University Child Metabolism and Nutrition Department.

RESULTS

There were 8 (57.2 %) females and 6 (42.8 %) males. Diagnoses of the patients were PMM2-CDG (n=4), PGM1-CDG (n=2), DPAGT1-CDG (n=2), SRD5A3-CDG (n=2), MPI-CDG (n=1), POMT2-CDG (n=1), B3GALNT2-CDG (n=1), DPM1-CDG (n=1). The clinical findings of the patients were dysmorphia (85.7 %), developmental delay (85.7 %), intellectual disability (85.7 %), ocular abnormalities (64.2 %), skeletal malformations (64.2 %), failure to thrive (57.1 %), microcephaly (57.1 %), hepatomegaly (35.7 %), hearing loss (35.7 %), seizures (28.5 %), gastrointestinal symptoms (21.4 %), endocrine abnormalities (21.4 %), and cardiac abnormalities (7.1 %). Laboratory findings were abnormal TIEF (92.8 %), abnormal liver enzymes (64.2 %), decreased protein C (64.2 %), decreased antithrombin III (64.2 %), decreased protein S (42.8 %), hypogammaglobulinemia (35.7 %), cerebellar hypoplasia (28.5 %), CK elevation (7.1 %), and hypoglycemia (7.1 %).

CONCLUSIONS

This study contributes to the literature by sharing our ultra-rare DPM1-CDG case with less than 20 cases in the literature and expanding the clinical and molecular characteristics of other CDG patients. Hyperinsulinemic hypoglycemia, short stature, hypothyroidism, growth hormone deficiency, hypogammaglobulinemia, pericardial effusion, elevated CK, congenital myasthenia, and anorectal malformation were unique findings that were observed. Cerebello-ocular findings accompanying multi-organ involvement were an essential clue for a possible CDG.

[Advances in the diagnosis and treatment of phosphomannomutase 2 deficiency]

Phosphomannomutase 2 deficiency is the most common form of N-glycosylation disorders and is also known as phosphomannomutase 2-congenital disorder of glycosylation (PMM2-CDG). It is an autosomal recessive disease with multi-system involvements and is caused by mutations in the PMM2 gene (OMIM: 601785), with varying severities in individuals. At present, there is still no specific therapy for PMM2-CDG, and early identification, early diagnosis, and early treatment can effectively prolong the life span of pediatric patients. This article reviews the advances in the diagnosis and treatment of PMM2-CDG.

Neurological Consequences of Congenital Disorders of Glycosylation

The chapter is devoted to neurological aspects of congenital disorders of glycosylation (CDG). At the beginning, the various types of CDG with neurological presentation of symptoms are summarized. Then, the occurrence of various neurological constellation of abnormalities (for example: epilepsy, brain anomalies on neuroimaging, ataxia, stroke-like episodes, autistic features) in different CDG types are discussed followed by data on possible biomarkers and limited treatment options.

Decreased cognitive function of ALG13KO female mice may be related to the decreased plasticity of hippocampal neurons

Asparagine-linked glycosylation 13 (ALG13) is an X-linked gene that encodes a protein involved in the glycosylation of the N-terminus. ALG13 deficiency leads to ALG13-congenital disorders of glycosylation (ALG13-CDG), usually in females presenting with mental retardation and epilepsy. Cognitive function is an important function of the hippocampus, and forms the basis for learning, memory and social abilities. However, researchers have not yet investigated the effect of ALG13 on hippocampal cognitive function. In this study, the exploration, learning, memory and social abilities of ALG13 knockout (KO) female mice were decreased in behavioral experiments. Golgi staining demonstrated a decrease in the complexity of hippocampal neurons. Western blot and immunofluorescence staining of the synaptic plasticity factors postsynaptic density protein 95 (PSD95) and synaptophysin (SYP) displayed varying degrees of decline. In other words, the KO of ALG13 may have reduced the expression of PSD95 and SYP in the hippocampus of female mice. Moreover, it may have lowered the synaptic plasticity in various areas of the hippocampus, thus resulting in decreased dendrite length, complexity, and dendrite spine density, which affected the hippocampal function and reduced the cognitive function in female mice.

A rare case of SRD5A3‐CDG in a patient with ataxia and telangiectasia: A case report

Steroid 5α‐reductase type 3 congenital disorder of glycosylation (SRD5A3‐CDG) is an extremely rare congenital disease. Common manifestations are developmental delay, intellectual disability, ophthalmological abnormalities, cerebellar abnormalities, ataxia, and hypotonia. Here, we discuss a seven‐year‐old boy with SRD5A3‐CDG (homozygous variant c.57G>A [p.Trp19Ter]), featuring the unprecedented finding of telangiectasia.

Nutrition interventions in congenital disorders of glycosylation

Congenital disorders of glycosylation (CDG) are a group of more than 160 inborn errors of metabolism affecting multiple pathways of protein and lipid glycosylation. Patients present with a wide range of symptoms and therapies are only available for very few subtypes. Specific nutritional treatment options for certain CDG types include oral supplementation of monosaccharide sugars, manganese, uridine, or pyridoxine. Additional management includes specific diets (i.e., complex carbohydrate or ketogenic diet), iron supplementation, and albumin infusions. We review the dietary management in CDG with a focus on two subgroups: N-linked glycosylation defects and GPI-anchor disorders.

SRD5A3-CDG: Twins with an intragenic tandem duplication

Steroid 5α-reductase type 3 congenital disorder of glycosylation (SRD5A3-CDG) is a rare metabolic disease mainly characterized by psychomotor disability, visual impairment, and variable eye malformations caused by bi-allelic pathogenic variants in SRD5A3. So far, only 23 distinct mutations were described. Exome sequencing in 32-year old monozygotic male twins revealed only the heterozygous splice variant c.562+3delG in SRD5A3, but no second variant. The twins presented with psychomotor deficit and a complex eye disease including retinal dystrophy, pallor of the papilla, nystagmus, and strabismus suggestive of SRD5A3-CDG. Only when applying exome-based copy number analysis, we identified as a second compound heterozygous variant a previously not reported tandem duplication of exons 2-4 in SRD5A3. Next to the typical skeletal anomalies of SRD5A3-CDG such as kyphosis and scoliosis, extension deficits of the proximal interphalangeal (PIP) joints IV were observed. Since similar contractures were described once in a patient with SRD5A3-CDG, we suggest that this rare symptom is possibly associated with SRD5A3-CDG. Our findings further expand the mutational and clinical spectrum of SRD5A3-CDG and emphasize the importance of an intragenic copy number analysis in patients with strong clinical suspicion of SRD5A3-CDG and only one detectable sequence variant.

A case with congenital disorder of glycosylation with defective fucosylation 2 and new mutation in FUK gene

INTRODUCTION

Congenital disorders of glycosylation (CDG) is a group of rare, hereditary, multisystem disorders, predominantly affecting nervous system. There are N- and O- types of glycosylation. Fucosylation, a form of N-glycosylation, involves many enzymes. Until today, type 1 and type 2 fucosylation defects were identified, having pathogenic variants in genes encoding α-1,6-fucosyltransferase and fucokinase enzymes, respectively. In this article, a patient with type 2 fucosylation defect will be presented, with hypotonia, developmental delay and blindness and a pathogenic variant that was previously described in two patients.

METHOD

Whole exome sequencing (WES) was performed, since the patient had no time to implement diagnostic algorithm for hypotonia etiology.

RESULTS

WES revealed a new pathogenic variant of homozygous c.993_1011del (p.Glu335Hisfs*55) frameshift variant of the FUK gene NM_145059 transcript. She had milder clinical manifestation than reported two patients.

CONCLUSION

Congenital Defect of Glycosylation should be considered when the clinical findings cannot be explained by other known diseases, particularly in patients with multisystemic, predominantly neurological involvement.

An Overview of Glycosylation and its Impact on Cardiovascular Health and Disease

The cardiovascular system is a complex and well-organized system in which glycosylation plays a vital role. The heart and vascular wall cells are constituted by an array of specific receptors; most of them are N- glycosylated and mucin-type O-glycosylated. There are also intracellular signaling pathways regulated by different post-translational modifications, including O-GlcNAcylation, which promote adequate responses to extracellular stimuli and signaling transduction. Herein, we provide an overview of N-glycosylation and O-glycosylation, including O-GlcNAcylation, and their role at different levels such as reception of signal, signal transduction, and exogenous molecules or agonists, which stimulate the heart and vascular wall cells with effects in different conditions, like the physiological status, ischemia/reperfusion, exercise, or during low-grade inflammation in diabetes and aging. Furthermore, mutations of glycosyltransferases and receptors are associated with development of cardiovascular diseases. The knowledge on glycosylation and its effects could be considered biochemical markers and might be useful as a therapeutic tool to control cardiovascular diseases.

ALG1-CDG Caused by Non-functional Alternative Splicing Involving a Novel Pathogenic Complex Allele

This study reports on a Mexican mestizo patient with a multi-systemic syndrome including neurological involvement and a type I serum transferrin profile. Clinical exome sequencing revealed complex alleles in ALG1, the encoding gene for the chitobiosyldiphosphodolichol beta-mannosyltransferase that participates in the formation of the dolichol-pyrophosphate-GlcNAc2Man5, a lipid-linked glycan intermediate during N-glycan synthesis. The identified complex alleles were NM_019109.5(ALG1): c.[208 + 16_208 + 19dup; 208 + 25G > T] and NM_019109.5(ALG1): c.[208 + 16_208 + 19dup; 1312C > T]. Although both alleles carried the benign variant c.208 + 16_208 + 19dup, one allele carried a known ALG1 pathogenic variant (c.1312C > T), while the other carried a new uncharacterized variant (c.208 + 25G > T) causing non-functional alternative splicing that, in conjunction with the benign variant, defines the pathogenic protein effect (p.N70S_S71ins9). The presence in the patient’s serum of the pathognomonic N-linked mannose-deprived tetrasaccharide marker for ALG1-CDG (Neu5Acα2,6Galβ1,4-GlcNAcβ1,4GlcNAc) further supported this diagnosis. This is the first report of an ALG1-CDG patient from Latin America.

Anthropometric Phenotype of Patients with PMM2-CDG

Background: Growth failure is commonly reported in children with PMM2-CDG. The aim of the study was to delineate the longitudinal anthropometric phenotype of patients with PMM2-CDG and attempt to find some correlations between the genotype and anthropometric phenotype. Materials and methods: Retrospective chart review of PMM2-CDG patients’ medical records was performed regarding the anthropometric measurements (head circumference, body length/height, body weight, body mass index) and PMM2 variants. Results: A negative tendency of growth evolution was observed. Patients found to be heterozygous for R141H grew slower than other patients. Body weight was correlated with body height. A negative tendency of the growth rate of head circumference was observed. Patients found to be heterozygous for R141H experienced slower growth than other patients. Conclusions: Long-term observational studies are essential to characterize the anthropometric phenotype. The body growth failure, as well as head circumference growth failure, were more severe in patients found to be heterozygous for R141H.

Congenital disorders of glycosylation: Prevalence, incidence and mutational spectrum in the Polish population

Introduction

The incidence and prevalence of congenital disorders of glycosylation (CDG) have not been well established. The aim of the study was to evaluate the prevalence, incidence and genotypes of CDG patients diagnosed during the last 23 years in Poland (1997 – 30th October 2020).

Material and methods

The diagnosis was based on serum Tf IEF which is performed at The Children's Memorial Health Institute (CMHI) in Warsaw. Based on demographic data, the prevalence of CDG among the Polish population in 2020 as well as the birth prevalence of CDG from 1990 to 2020 were estimated.

Results

39 patients (from 35 families) with molecularly confirmed CDG were diagnosed, including 17 (44%) patients (from 16 families) with PMM2-CDG. The c.422G > A, p.Arg141His and c.691G > A, p.Val231Met pathogenic missense variants were the most common identified PMM2 variants. Eleven other patients were diagnosed with CDG based on serum Tf IEF analysis only; the molecular analysis is pending. Ten CDG patients died, including 6 with PMM2-CDG, 1 with PGM1-CDG and 1 with DPAGT1-CDG. The prevalence of CDG in the Polish population was estimated at approximately 1 per million while that of PMM2 at 0.4 per million. The annual incidence of CDG was estimated at 0.013 per 100,000 people in 2020.

Conclusions

A low frequence of CDG in our study could be underestimated.

Liver Involvement in Congenital Disorders of Glycosylation and Deglycosylation

Background: Congenital disorders of glycosylation (CDG) and NGLY1-CDDG (NGLY1-congenital disorder of deglycosylation) usually represent multisystem (especially neurovisceral) diseases with liver involvement reported in some of them. The aim of the study was to characterize the liver phenotype in CDG and NGLY1-CDDG patients hospitalized in our Institute, and to find the most specific features of liver disease among them. Material and Methods: The study involved 39 patients (from 35 families) with CDG, and two patients (from two families) with NGLY1-CDDG, confirmed molecularly, for whom detailed characteristics of liver involvement were available. They were enrolled based on the retrospective analysis of their medical records. Results: At the time of the first consultation, 13/32 patients were diagnosed with hepatomegaly; none of them with splenomegaly. As many as 23/32 persons had elevated serum transaminases, including 16 (70%) who had mildly elevated levels. During the long-term follow-up (available for 19 patients), serum transaminases normalized in 15/19 (79%) of them, including a spontaneous normalization in 12/15 (80%) of them. The GGT activity was observed to be normal in all study cases. Protein C, protein S and antithrombin activities in plasma were observed in 16 patients, and they were decreased in all of them. Conclusions: It is necessary to conduct a long-term follow-up of liver disease in CDG to obtain comprehensive data.

Congenital Disorders of Glycosylation: What Clinicians Need to Know?

Congenital disorders of glycosylation (CDG) are a group of clinically heterogeneous disorders characterized by defects in the synthesis of glycans and their attachment to proteins and lipids. This manuscript aims to provide a classification of the clinical presentation, diagnostic methods, and treatment of CDG based on the literature review and our own experience (referral center in Poland). A diagnostic algorithm for CDG was also proposed. Isoelectric focusing (IEF) of serum transferrin (Tf) is still the method of choice for diagnosing N-glycosylation disorders associated with sialic acid deficiency. Nowadays, high-performance liquid chromatography, capillary zone electrophoresis, and mass spectrometry techniques are used, although they are not routinely available. Since next-generation sequencing became more widely available, an improvement in diagnostics has been observed, with more patients and novel CDG subtypes being reported. Early and accurate diagnosis of CDG is crucial for timely implementation of appropriate therapies and improving clinical outcomes. However, causative treatment is available only for few CDG types.