Nonimmune hydrops fetalis and congenital disorders of glycosylation: A systematic literature review

Diagnosis of inborn errors of metabolism through prenatal exome sequencing with targeted analysis for fetal structural anomalies

OBJECTIVES

The value of prenatal exome sequencing (pES) for fetuses with structural anomalies is widely reported. In England, testing is conducted through trio exome sequencing and analysis of a gene panel. Over a 30-month period testing of 921 pregnancies resulted in a genetic diagnosis in 32.8% of cases (302/921). Here we review cases diagnosed with an inborn error of metabolism.

METHODS

Diagnoses of inborn errors of metabolism (IEM) were classified according to the ICIMD classification system. Genetic diagnoses were assessed against Human Phenotype Ontology terms, gestation of scan findings and literature evidence.

RESULTS

35/302 diagnoses (11.6%) represented IEM. Almost half affected metabolism of complex macromolecules and organelles (n = 16), including congenital disorders of glycosylation (n = 8), peroxisome biogenesis disorders (n = 4), and lysosomal storage disorders (n = 4). There were eight disorders of lipid metabolism and transport, the majority being genes in the cholesterol biosynthesis pathway, eight disorders of intermediary metabolism, of which seven were defects in "energy" processes, and two diagnoses of alkaline phosphatase deficiency.

CONCLUSIONS

Review of pES diagnoses and ultrasound scan findings is key to understanding genotype-phenotype correlations. IEM are genetically heterogeneous and may present with variable scan findings, which makes an individual diagnosis difficult to suspect. Diagnosis during pregnancy is particularly important for many IEM with respect to prognosis and early neonatal management.

Inherited Thrombocytopenia Caused by Variants in Crucial Genes for Glycosylation

Protein glycosylation, including sialylation, involves complex and frequent post-translational modifications, which play a critical role in different biological processes. The conjugation of carbohydrate residues to specific molecules and receptors is critical for normal hematopoiesis, as it favors the proliferation and clearance of hematopoietic precursors. Through this mechanism, the circulating platelet count is controlled by the appropriate platelet production by megakaryocytes, and the kinetics of platelet clearance. Platelets have a half-life in blood ranging from 8 to 11 days, after which they lose the final sialic acid and are recognized by receptors in the liver and eliminated from the bloodstream. This favors the transduction of thrombopoietin, which induces megakaryopoiesis to produce new platelets. More than two hundred enzymes are responsible for proper glycosylation and sialylation. In recent years, novel disorders of glycosylation caused by molecular variants in multiple genes have been described. The phenotype of the patients with genetic alterations in GNE, SLC35A1, GALE and B4GALT is consistent with syndromic manifestations, severe inherited thrombocytopenia, and hemorrhagic complications.

Diagnostic yield from prenatal exome sequencing for non-immune hydrops fetalis: A systematic review and meta-analysis

Non-immune hydrops fetalis (NIHF) has multiple genetic etiologies diagnosable by exome sequencing (ES). We evaluated the yield of prenatal ES for NIHF, and the contribution of additional clinical findings and history. Systematic review was performed with PROSPERO tag 232951 using CINAHL, PubMed, and Ovid MEDLINE from January 1, 2000 through December 1, 2021. Selected studies performed ES to augment standard prenatal diagnostic approaches. Cases meeting a strict NIHF phenotype were tabulated with structured data imputed from papers or requested from authors. Genetic variants and diagnostic outcomes were harmonized across studies using current ACMG and ClinGen variant classification guidelines. Thirty-one studies reporting 445 NIHF cases had a 37% (95% CI: 32%-41%) diagnostic rate. There was no significant difference between isolated NIHF and NIHF with fetal malformations or between recurrent and simplex cases. Diagnostic rate was higher for consanguineous than non-consanguineous cases. Disease categories included RASopathies (24%), neuromuscular (21%), metabolic (17%), lymphatic (13%), other syndromes (9%), cardiovascular (5%), hematologic (2%), skeletal (2%), and other categories (7%). Inheritance patterns included recessive (55%), dominant (41%), and X-linked (4%). ES should be considered in the diagnostic workup of NIHF with and without associated ultrasound findings regardless of history of recurrence or consanguinity.

N-Glycosylation Deficiency Reduces the Activation of Protein C and Disrupts the Endothelial Barrier Integrity

Phosphomannomutase 2 (PMM2) deficiency is the most prevalent congenital disorder of glycosylation. It is associated with coagulopathy, including protein C deficiency. Since all components of the anticoagulant and cytoprotective protein C system are glycosylated, we sought to investigate the impact of an N-glycosylation deficiency on this system as a whole. To this end, we developed a PMM2 knockdown model in the brain endothelial cell line hCMEC/D3. The resulting PMM2^low cells were less able to generate activated protein C (APC), due to lower surface expression of thrombomodulin and endothelial protein C receptor. The low protein levels were due to downregulated transcription of the corresponding genes (THBD and PROCR, respectively), which itself was related to downregulation of transcription regulators Krüppel-like factors 2 and 4 and forkhead box C2. PMM2 knockdown was also associated with impaired integrity of the endothelial cell monolayer-partly due to an alteration in the structure of VE-cadherin in adherens junctions. The expression of protease-activated receptor 1 (involved in the cytoprotective effects of APC on the endothelium) was not affected by PMM2 knockdown. Thrombin stimulation induced hyperpermeability in PMM2^low cells. However, pretreatment of cells with APC before thrombin simulation was still associated with a barrier-protecting effect. Taken as a whole, our results show that the partial loss of PMM2 in hCMEC/D3 cells is associated with impaired activation of protein C and a relative increase in barrier permeability.

Hydrops fetalis-trends in associated diagnoses and mortality from 1997-2018

OBJECTIVES

To describe and evaluate trends in the etiology and mortality risk in neonates admitted for neonatal intensive care with hydrops fetalis.

STUDY DESIGN

A retrospective review of de-identified patient data in the Pediatrix Clinical Data Warehouse from 1997 to 2018.

RESULTS

We identified 2144 infants diagnosed with hydrops fetalis. The most common diagnoses were congenital heart disease (n = 325, 15.2%), genetic diagnoses (n = 269, 12.5%) and cardiac arrhythmia (n = 176, 8.2%). Of 2144 neonates, 988 (46%) survived to hospital discharge and 775 (36%) died prior to discharge. Mortality rate was highly variable across diagnoses, ranging from 90% in infants with congenital diaphragmatic hernia to 0% in infants with atrial flutter. Over the study period, more infants were diagnosed with trisomies and fewer with twin-to-twin transfusion. Mortality decreased by 5% from 1997-2007 to 2008-2018.

CONCLUSIONS

The risk of death among neonates with hydrops fetalis is highly dependent on the underlying cause, with increasing risk of mortality at lower gestational ages.

NANS-CDG: Delineation of the Genetic, Biochemical, and Clinical Spectrum

Background: NANS-CDG is a recently described congenital disorder of glycosylation caused by biallelic genetic variants in NANS, encoding an essential enzyme in de novo sialic acid synthesis. Sialic acid at the end of glycoconjugates plays a key role in biological processes such as brain and skeletal development. Here, we present an observational cohort study to delineate the genetic, biochemical, and clinical phenotype and assess possible correlations.

Methods: Medical and laboratory records were reviewed with retrospective extraction and analysis of genetic, biochemical, and clinical data (2016–2020).

Results: Nine NANS-CDG patients (nine families, six countries) referred to the Radboudumc CDG Center of Expertise were included. Phenotyping confirmed the hallmark features including intellectual developmental disorder (IDD) (n = 9/9; 100%), facial dysmorphisms (n = 9/9; 100%), neurologic impairment (n = 9/9; 100%), short stature (n = 8/9; 89%), skeletal dysplasia (n = 8/9; 89%), and short limbs (n = 8/9; 89%). Newly identified features include ophthalmological abnormalities (n = 6/9; 67%), an abnormal septum pellucidum (n = 6/9; 67%), (progressive) cerebral atrophy and ventricular dilatation (n = 5/9; 56%), gastrointestinal dysfunction (n = 5/9; 56%), thrombocytopenia (n = 5/9; 56%), and hypo–low-density lipoprotein cholesterol (n = 4/9; 44%). Biochemically, elevated urinary excretion of N-acetylmannosamine (ManNAc) is pathognomonic, the concentrations of which show a significant correlation with clinical severity. Genotypically, eight novel NANS variants were identified. Three severely affected patients harbored identical compound heterozygous pathogenic variants, one of whom was initiated on experimental prenatal and postnatal treatment with oral sialic acid. This patient showed markedly better psychomotor development than the other two genotypically identical males.

Conclusions: ManNAc screening should be considered in all patients with IDD, short stature with short limbs, facial dysmorphisms, neurologic impairment, and an abnormal septum pellucidum +/– congenital and neurodegenerative lesions on brain imaging, to establish a precise diagnosis and contribute to prognostication. Personalized management includes accurate genetic counseling and access to proper supports and tailored care for gastrointestinal symptoms, thrombocytopenia, and epilepsy, as well as rehabilitation services for cognitive and physical impairments. Motivated by the short-term positive effects of experimental treatment with oral sialic, we have initiated this intervention with protocolized follow-up of neurologic, systemic, and growth outcomes in four patients. Research is ongoing to unravel pathophysiology and identify novel therapeutic targets.

High diagnosis rate for nonimmune hydrops fetalis with prenatal clinical exome from the Hydrops-Yielding Diagnostic Results of Prenatal Sequencing (HYDROPS) Study

PURPOSE

Nonimmune hydrops fetalis (NIHF) presents as life-threatening fluid collections in multiple fetal compartments and can be caused by both genetic and non-genetic etiologies. We explored incremental diagnostic yield of testing with prenatal exome sequencing (ES) for NIHF following a negative standard NIHF workup.

METHODS

Participants enrolled into the Hydrops-Yielding Diagnostic Results of Prenatal Sequencing (HYDROPS) study met a strict definition of NIHF and had negative standard-of-care workup. Clinical trio ES from fetal samples and parental blood was performed at a CLIA-certified reference laboratory with clinical reports returned by geneticists and genetic counselors. Negative exomes were reanalyzed with information from subsequent ultrasounds and records.

RESULTS

Twenty-two fetal exomes reported 11 (50%) diagnostic results and five possible diagnoses (22.7%). Diagnosed cases comprised seven de novodominant disorders, three recessive disorders, and one inherited dominant disorder including four Noonan syndromes (PTPN11, RAF1, RIT1, and RRAS2), three musculoskeletal disorders (RYR1, AMER1, and BICD2), two metabolic disorders (sialidosis and multiple sulfatase deficiency), one Kabuki syndrome, and one congenital anemia (KLF1).

CONCLUSION

The etiology of NIHF predicts postnatal prognosis and recurrence risk in future pregnancies. ES provides high incremental diagnostic yield for NIHF after standard-of-care testing and should be considered in the workup.

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

Background

Congenital disorders of glycosylation (CDG) result from defects in the synthesis of glycans and the attachment of glycans to proteins and lipids. Our study aimed to describe the clinical, biochemical, and molecular findings of CDG patients, and to present the long-term follow-up.

Material and methods

A single-center study (1995–2019 years) of patients with congenital disorders of N-glycosylation and combined N- and O-hypoglycosylation was performed.

Results

Among 32 patients included into the study, there were 12 PMM2-CDG, 3 ALG13-CDG, 3 ALG1-CDG, 1 ALG3-CDG, 3 MPI-CDG, 1 PGM1-CDG, 4 SRD5A3-CDG, 1 DPAGT1-CDG, 3 ATP6AP1-CDG, 1 ATP6V0A2-CDG. The phenotypic and genotypic spectrum during long-term (in some cases over 20 years) observation was characterised and several measurements of serum Tf isoforms taken. Statistical analysis revealed strong negative correlation between asialo-Tf and tetrasialo-Tf, as well as between disialo-Tf and tetrasialo-Tf. Within CDG type I, no difference in % Tf isoforms was revealed between PMM2-CDG and non-PMM2-CDG patients. However, these two groups differed significantly in such diagnostic features as: cerebellar ataxia, failure to thrive, hypothyroidism, pericardial effusion, cardiomyopathy, inverted nipples, prolonged INR.

The effect of treatment with mannose in 2 patients with MPI-CDG was assessed and we found that % of asialo-Tf, monosialo-Tf, and disialo-Tf was significantly lowered, whereas tetrasialo-Tf and pentasialo-Tf rose, coming closer or falling into the reference range.

Conclusions

The novel finding was an abnormal Tf IEF pattern in two ALG13-CDG patients and normal in one ALG1-CDG patient. Clinical manifestation of presented CDG patients was similar to that reported in the literature. Mannose supplementation in MPI-CDG patients, as well as galactose supplementation in PGM1-CDG patient, improved patients’ clinical picture and Tf isoform profiles.

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.

Golgi inCOGnito: From vesicle tethering to human disease

The Conserved Oligomeric Golgi (COG) complex, a multi-subunit vesicle tethering complex of the CATCHR (Complexes Associated with Tethering Containing Helical Rods) family, controls several aspects of cellular homeostasis by orchestrating retrograde vesicle traffic within the Golgi. The COG complex interacts with all key players regulating intra-Golgi trafficking, namely SNAREs, SNARE-interacting proteins, Rabs, coiled-coil tethers, and vesicular coats. In cells, COG deficiencies result in the accumulation of non-tethered COG-complex dependent (CCD) vesicles, dramatic morphological and functional abnormalities of the Golgi and endosomes, severe defects in N- and O- glycosylation, Golgi retrograde trafficking, sorting and protein secretion. In humans, COG mutations lead to severe multi-systemic diseases known as COG-Congenital Disorders of Glycosylation (COG-CDG). In this report, we review the current knowledge of the COG complex and analyze COG-related trafficking and glycosylation defects in COG-CDG patients.

A systematic review of monogenic etiologies of nonimmune hydrops fetalis

Hydrops Fetalis (HF), accumulation of fluid in two or more fetal compartments, is life-threatening to the fetus. Genetic etiologies include many chromosomal and monogenic disorders. Despite this, the clinical workup typically evaluates limited genetic targets. To support broader molecular testing of pregnancies with HF, we cataloged the spectrum of monogenic disorders associated with nonimmune hydrops fetalis (NIHF).

We performed a systematic literature review under PROSPERO tag CRD42018099495 of cases reporting NIHF meeting strict phenotypic criteria and well-defined genetic diagnosis. We ranked the evidence per gene based on number of reported cases, phenotype and molecular/biochemical diagnosis.

We identified 131 genes with strong evidence for an association with NIHF and 46 genes with emerging evidence spanning the spectrum of multisystem syndromes, cardiac disorders, hematologic disorders, and metabolic disorders. Several genes previously implicated with NIHF did not have any reported cases in the literature with both fetal hydrops and molecular diagnosis. Many genes with strong evidence for association with NIHF would not be detected using current sequencing panels.

Nonimmune HF has many possible monogenic etiologies, several with treatment implications, but current diagnostic approaches are not exhaustive. Studies are needed to assess if broad sequencing approaches like whole exome sequencing are useful in clinical management of HF.

Immune dysfunction in MGAT2-CDG: A clinical report and review of the literature

Glycosylation is a critical post/peri-translational modification required for the appropriate development and function of the immune system. As an example, abnormalities in glycosylation can cause antibody deficiency and reduced lymphocyte signaling, although the phenotype can be complex given the diverse roles of glycosylation. Human MGAT2 encodes N-acetylglucosaminyltransferase II, which is a critical enzyme in the processing of oligomannose to complex N-glycans. Complex N-glycans are essential for immune system functionality, but only one individual with MGAT2-CDG has been described to have an abnormal immunologic evaluation. MGAT2-CDG (CDG-IIa) is a congenital disorder of glycosylation (CDG) associated with profound global developmental disability, hypotonia, early onset epilepsy, and other multisystem manifestations. Here, we report a 4-year old female with MGAT2-CDG due to a novel homozygous pathogenic variant in MGAT2, a 4-base pair deletion, c.1006_1009delGACA. In addition to clinical features previously described in MGAT2-CDG, she experienced episodic asystole, persistent hypogammaglobulinemia, and defective ex vivo mitogen and antigen proliferative responses, but intact specific vaccine antibody titers. Her infection history has been mild despite the testing abnormalities. We compare this patient to the 15 previously reported patients in the literature, thus expanding both the genotypic and phenotypic spectrum for MGAT2-CDG.

Platelets and Defective N-Glycosylation

N-glycans are covalently linked to an asparagine residue in a simple acceptor sequence of proteins, called a sequon. This modification is important for protein folding, enhancing thermodynamic stability, and decreasing abnormal protein aggregation within the endoplasmic reticulum (ER), for the lifetime and for the subcellular localization of proteins besides other functions. Hypoglycosylation is the hallmark of a group of rare genetic diseases called congenital disorders of glycosylation (CDG). These diseases are due to defects in glycan synthesis, processing, and attachment to proteins and lipids, thereby modifying signaling functions and metabolic pathways. Defects in N-glycosylation and O-glycosylation constitute the largest CDG groups. Clotting and anticlotting factor defects as well as a tendency to thrombosis or bleeding have been described in CDG patients. However, N-glycosylation of platelet proteins has been poorly investigated in CDG. In this review, we highlight normal and deficient N-glycosylation of platelet-derived molecules and discuss the involvement of platelets in the congenital disorders of N-glycosylation.