Congenital nephrotic syndrome in an infant with ALG1-congenital disorder of glycosylation

Normal transferrin glycosylation does not rule out severe ALG1 deficiency

ALG1-CDG is a rare, clinically variable metabolic disease, caused by the defect of adding the first mannose (Man) to N-acetylglucosamine (GlcNAc2)-pyrophosphate (PP)-dolichol to the growing oligosaccharide chain, resulting in impaired N-glycosylation of proteins. N-glycosylation has a key role in functionality, stability, and half-life of most proteins. Therefore, congenital defects of glycosylation typically are multisystem disorders. Here we report a 3-year-old patient with severe neurological, cardiovascular, respiratory, musculoskeletal and gastrointestinal symptoms. ALG1-CDG was suggested based on exome sequencing and Western blot analysis. Despite her severe clinical manifestations and genetic diagnosis, serum transferrin glycoform analysis was normal. Western blot analysis of highly glycosylated proteins in fibroblasts revealed decreased intercellular adhesion molecule 1 (ICAM1), but normal lysosomal associated membrane protein 1 and 2 (LAMP1 and LAMP2) expression levels. Glycoproteomics in fibroblasts showed the presence of the abnormal tetrasacharide. Reviewing the literature, we found 86 reported ALG1-CDG patients, but only one with normal transferrin analysis. Based on our results we would like to highlight the importance of multiple approaches in diagnosing ALG1-CDG, as normal serum transferrin glycosylation or other biomarkers with normal expression levels can occur.

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.

Analysis of clinical phenotypic and genotypic spectra in 36 children patients with Epilepsy of Infancy with Migrating Focal Seizures

Epilepsy of Infancy with Migrating Focal Seizures (EIMFS) is a rare developmental and epileptic encephalopathy (DEEs) with unknown etiology, and poor prognosis. In order to explore new genetic etiology of EIMFS and new precision medicine treatment strategies, 36 children with EIMFS were enrolled in this study. 17/36 cases had causative variants across 11 genes, including 6 novel EIMFS genes: PCDH19, ALDH7A1, DOCK6, PRRT2, ALG1 and ATP7A. 13/36 patients had ineffective seizure control, 14/36 patients had severe retardation and 6/36 patients died. Of them, the genes for ineffective seizure control, severe retardation or death include KCNT1, SCN2A, SCN1A, ALG1, ATP7A and WWOX. 17 patients had abnormal MRI, of which 8 had ineffective seizure control, 7 had severe retardation and 4 died. 13 patients had hypsarrhythmia, of which 6 had ineffective seizure control, 6 had severe retardation and 2 died. Also, 7 patients had burst suppression, of which 1 had ineffective seizure control, 3 had severe retardation and 3 died. This study is the first to report that ALDH7A1, ATP7A, DOCK6, PRRT2, ALG1, and PCDH19 mutations cause the phenotypic spectrum of EIMFS to expand the genotypic spectrum. The genes KCNT1, SCN2A, SCN1A, ALG1, ATP7A and WWOX may be associated with poor prognosis. The patients presenting with MRI abnormalities, hypsarrhythmia and burst suppression in EEG may be associated with poor prognosis.

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.

Peritoneal dialysis outcomes in patients with nephrotic syndrome: a propensity score-matched cohort study

INTRODUCTION

It is unclear whether patients with end-stage renal disease (ESRD) and nephrotic syndrome (NS) can be treated with peritoneal dialysis (PD).

OBJECTIVES

To investigate the outcomes of PD treatment in ESRD patients with or without NS.

METHODS

In this retrospective cohort study, all incident patients with ESRD and NS who started PD from 1 February 2006 to 31 December 2017, were matched with patients without NS using propensity scores based on age, sex, diabetes mellitus status, and serum albumin.

RESULTS

Fifty-three patients in the NS PD group and 53 matched controls were included. The median survival of the NS PD group was comparable to that of the non-NS PD group. An interaction effect was observed between survival time and baseline NS status. Thus, patients' outcomes within and after 1.5 years were analyzed separately. Both mortality (log-rank test, p= .235) and technique failure (log-rank test, p= .543) rates within 1.5 years in patients with NS were comparable to those of the non-NS group. After 1.5 years, however, the NS status at baseline was associated with lower all-cause mortality (p= .020) and lower technique failure (p= .008) rates in PD patients compared with the non-NS group. The multivariable Cox regression analysis showed that compared with the patients in the non-NS PD group, PD patients with NS had both significantly lower all-cause mortality and lower technique failure rate after adjusting for other factors.

CONCLUSIONS

Our study indicates that PD may be considered as a long-term renal replacement therapy for patients with ESRD and baseline NS.

CDG and immune response: From bedside to bench and back

Glycosylation is an essential biological process that adds structural and functional diversity to cells and molecules, participating in physiological processes such as immunity. The immune response is driven and modulated by protein-attached glycans that mediate cell-cell interactions, pathogen recognition and cell activation. Therefore, abnormal glycosylation can be associated with deranged immune responses. Within human diseases presenting immunological defects are congenital disorders of glycosylation (CDG), a family of around 130 rare and complex genetic diseases. In this review, we have identified 23 CDG with immunological involvement, characterized by an increased propensity to-often life-threatening-infection. Inflammatory and autoimmune complications were found in 7 CDG types. CDG natural history(ies) and the mechanisms behind the immunological anomalies are still poorly understood. However, in some cases, alterations in pathogen recognition and intracellular signaling (eg, TGF-β1, NFAT, and NF-κB) have been suggested. Targeted therapies to restore immune defects are only available for PGM3-CDG and SLC35C1-CDG. Fostering research on glycoimmunology may elucidate the involved pathophysiological mechanisms and open new therapeutic avenues, thus improving CDG patients' quality of life.

Podocyte-Specific Sialylation-Deficient Mice Serve as a Model for Human FSGS

BACKGROUND

The etiology of steroid-resistant nephrotic syndrome, which manifests as FSGS, is not completely understood. Aberrant glycosylation is an often underestimated factor for pathologic processes, and structural changes in the glomerular endothelial glycocalyx have been correlated with models of nephrotic syndrome. Glycans are frequently capped by sialic acid (Sia), and sialylation's crucial role for kidney function is well known. Human podocytes are highly sialylated; however, sialylation's role in podocyte homeostasis remains unclear.

METHODS

We generated a podocyte-specific sialylation-deficient mouse model (PCmas^-/- ) by targeting CMP-Sia synthetase, and used histologic and ultrastructural analysis to decipher the phenotype. We applied CRISPR/Cas9 technology to generate immortalized sialylation-deficient podocytes (asialo-podocytes) for functional studies.

RESULTS

Progressive loss of sialylation in PCmas^-/- mice resulted in onset of proteinuria around postnatal day 28, accompanied by foot process effacement and loss of slit diaphragms. Podocyte injury led to severe glomerular defects, including expanded capillary lumen, mesangial hypercellularity, synechiae formation, and podocyte loss. In vivo, loss of sialylation resulted in mislocalization of slit diaphragm components, whereas podocalyxin localization was preserved. In vitro, asialo-podocytes were viable, able to proliferate and differentiate, but showed impaired adhesion to collagen IV.

CONCLUSIONS

Loss of cell-surface sialylation in mice resulted in disturbance of podocyte homeostasis and FSGS development. Impaired podocyte adhesion to the glomerular basement membrane most likely contributed to disease development. Our data support the notion that loss of sialylation might be part of the complex process causing FSGS. Sialylation, such as through a Sia supplementation therapy, might provide a new therapeutic strategy to cure or delay FSGS and potentially other glomerulopathies.