Familial steroid-sensitive nephrotic syndrome in Southern Israel: clinical and genetic observations

Relationships between the clinical phenotypes and genetic variants associated with the immunological mechanism in childhood idiopathic nephrotic syndrome: protocol for a prospective observational single-centre cohort study

INTRODUCTION

Idiopathic nephrotic syndrome (INS) is the most common glomerulopathy that results in childhood chronic kidney disease in China, but the relationships between different clinical phenotypes and immunological genetic variants observed in patients with INS are ambiguous and have not been well studied. A cohort study combined with whole exome sequencing might further identify the effects of immunological genetic variants on clinical phenotypes and treatment outcomes.

METHODS AND ANALYSIS

We describe a 3 year prospective observational single-centre cohort study to be conducted in the Children's Hospital of Chongqing Medical University in China. This study will recruit and investigate 336 patients with childhood-onset INS presenting with different clinical phenotypes. Whole exome sequencing will be conducted when patients progress to a confirmed clinical phenotype during follow-up. Relevant clinical and epidemiological data, as well as conventional specimens, will be collected at study entry and 1 month, 3 months, 6 months, 1 year, 2 years and 3 years after disease onset. After this cohort is generated, the immunological genetic variants of steroid-sensitive nephrotic syndrome without frequent relapse, steroid-resistant nephrotic syndrome and steroid-dependent/frequent relapse nephrotic syndrome will be evaluated.

ETHICS AND DISSEMINATION

The study protocol is approved by Ethics Committee of Children's Hospital of Chongqing Medical University (reference number 2018-140). The results will be disseminated through peer-reviewed journals and conference presentations.

TRIAL REGISTRATION NUMBER

ChiCTR1800019795.

Phospholipase C-Gamma 2 Activity in Familial Steroid-Sensitive Nephrotic Syndrome

BACKGROUND

Familial Steroid-sensitive Nephrotic Syndrome (SSNS) is rare, complicating the identification of candidate genes. A recent population-based approach study of SSNS identified HLA-DQA1 and Phospholipase C-Gamma 2 (PLCG2) missense coding variants as candidate loci. PLCG2 is a signaling molecule regulated by phosphorylation and is critical for Ca²⁺ flux in cells of the immune system.

METHODS

In order to detect a candidate gene for familial SSNS, we conducted an whole-exome sequencing in a pedigree consisting of two healthy parents, two non-identical twin brothers with SSNS, and a healthy young sibling. Flow cytometric assays were conducted to investigate the effects of the identified PLCG2 rare variants on B cell receptor-mediated PLCG2 tyrosine 759 phosphorylation, as well as on Ca²⁺ flux.

RESULTS

Two missense rare variants in the PLCG2 gene were detected in the affected twins. An increase in tyrosine phosphorylation of PLCG2 as well as more rapid Ca²⁺ flux were noted in response to stimulation in the affected twins compared to their parents.

CONCLUSIONS

Rare variants in PLCG2 segregated with disease in familial SSNS. Functional studies suggest the combined rare variants result in a gain of function in PLCG2 activity. Taken together, these results support PLCG2 as a possible candidate locus for familial SSNS.

Clinical and genetic heterogeneity in familial steroid-sensitive nephrotic syndrome

BACKGROUND

Familial steroid-sensitive nephrotic syndrome (SSNS) is a rare condition. The disease pathophysiology remains elusive. However, bi-allelic mutations in the EMP2 gene were identified, and specific variations in HLA-DQA1 were linked to a high risk of developing the disease.

METHODS

Clinical data were analyzed in 59 SSNS families. EMP2 gene was sequenced in families with a potential autosomal recessive (AR) inheritance. Exome sequencing was performed in a subset of 13 families with potential AR inheritance. Two variations in HLA-DQA1 were genotyped in the whole cohort.

RESULTS

Transmission was compatible with an AR (n = 33) or autosomal dominant (AD, n = 26) inheritance, assuming that familial SSNS is a monogenic trait. Clinical features did not differ between AR and AD groups. All patients, including primary (n = 7) and secondary steroid resistant nephrotic syndrone (SRNS), (n = 13) were sensitive to additional immunosuppressive therapy. Both HLA-DQA1 variations were found to be highly linked to the disease (OR = 4.34 and OR = 4.89; p < 0.001). Exome sequencing did not reveal any pathogenic mutation, neither did EMP2 sequencing.

CONCLUSIONS

Taken together, these results highlight the clinical and genetic heterogeneity in familial SSNS. Clinical findings sustain an immune origin in all patients, whatever the initial steroid-sensitivity. The absence of a variant shared by two families and the HLA-DQA1 variation enrichments suggest a complex mode of inheritance.

Genetics of childhood steroid-sensitive nephrotic syndrome

The pathogenesis of childhood-onset nephrotic syndrome (NS), disparity in incidence of NS among races, and variable responses to therapies in children with NS have defied explanation to date. In the last 20 years over 50 genetic causes of steroid-resistant nephrotic syndrome (SRNS) have been identified, and at least two disease loci for two pathologic variants of SRNS (focal segmental glomerulosclerosis and membranous nephropathy) have been defined. However, the genetic causes and risk loci for steroid-sensitive nephrotic syndrome (SSNS) remain elusive, partly because SSNS is relatively rare and also because cases of SSNS vary widely in phenotypic expression over time. A recent study of a well-defined modest cohort of children with SSNS identified variants in HLA-DQA1 as a risk factor for SSNS. Here we review what is currently known about the genetics of SSNS and also discuss how recent careful phenotypic and genomic studies reinforce the role of adaptive immunity in the molecular mechanisms of SSNS.

The incidence of the nephrotic syndrome in childhood in Germany

BACKGROUND

The incidence of childhood nephrotic syndrome (NS) in Germany is not well known.

METHODS

An ESPED-based nationwide collection of epidemiological data of children in 2005 and 2006.

RESULT

The mean age of NS at onset was 5.5 ± 3.7 years. The gender ratio of boys to girls was 1.8:1. The average length of stay was 15.5 ± 11.2 days, with younger children remaining significantly longer in hospital. Steroid-resistance was more common in children ≥8 years (p = 0.023). Focal-segmental glomerulosclerosis (FSGS) was more common in children >10 years (p = 0.029). The ratio of males to females with FSGS was 1:1.9, thus the FSGS risk for girls at onset was 3.3-times greater. Considering the available data, the incidence of NS in Germany is 1.2/100,000 in the population <18 years, of which 1.0/100,000 are steroid-sensitive.

CONCLUSION

Compared with international data, which primarily focused on regional and small populations, this is the largest study about the incidence of the childhood NS.

R229Q Polymorphism of NPHS2 Gene in Group of Iraqi Children with Steroid-Resistant Nephrotic Syndrome

Background. The polymorphism R229Q is one of the most commonly reported podocin sequence variations among steroid-resistant nephrotic syndromes (SRNS). Aim of the Study. We investigated the frequency and risk of this polymorphism among a group of Iraqi children with SRNS and steroid-sensitive nephrotic syndrome (SSNS). Patients and Methods. A prospective case control study which was conducted in Al-Imamein Al-Kadhimein Medical City, spanning the period from the 1st of April 2015 to 30th of November 2015. Study sample consisted of 54 children having NS, divided into 2 groups: patients group consisted of 27 children with SRNS, and control group involved 27 children with SSNS. Both were screened by real time polymerase chain reaction for R229Q in exon 5 of NPHS2 gene. Results. Molecular study showed R229Q polymorphism in 96.3% of SRNS and 100% of SSNS. There were no phenotypic or histologic characteristics of patients bearing homozygous R229Q polymorphism and the patients with heterozygous R229Q polymorphism. Conclusion. Polymorphism R229Q of NPHS2 gene is prevalent in Iraqi children with SRNS and SSNS. Further study needs to be done, for other exons and polymorphism of NPHS2 gene in those patients.

Two new families with hereditary minimal change disease

BACKGROUND

Steroid-sensitive idiopathic nephrotic syndrome (SSINS) is most often encountered in sporadic cases of minimal change disease (MCD). Only rare cases of familial forms of MCD have been reported and most of them only in one generation. The scarcity of data has precluded unraveling the underlying genetic defect and candidate gene approaches have been unsuccessful. Here we report two families with related SSINS cases and review the related literature.

CASE PRESENTATION

Two siblings and a cousin (first family), and a father and his son (second family), are reported with SSINS due to MCD. Patients have been followed up for more than 12 years and a renal biopsy was performed in three cases, demonstrating typical features of MCD. The course of the disease was remarkable because of several relapses treated with steroids. In three cases, mycophenolate mofetil or cyclosporine was added.

CONCLUSION

Familial SSINS due to MCD is extremely rare and no genetic defect has been identified so far. Reporting cases of hereditary MCD will allow further genetic studies which will ultimately help unravel the molecular basis of this disease.

Molecular and genetic basis of inherited nephrotic syndrome

Nephrotic syndrome is an heterogeneous disease characterized by increased permeability of the glomerular filtration barrier for macromolecules. Podocytes, the visceral epithelial cells of glomerulus, play critical role in ultrafiltration of plasma and are involved in a wide number of inherited and acquired glomerular diseases. The identification of mutations in nephrin and other podocyte genes as causes of genetic forms of nephrotic syndrome has revealed new important aspects of the pathogenesis of proteinuric kidney diseases and expanded our knowledge of the glomerular biology. Moreover, a novel concept of a highly dynamic slit diaphragm proteins is emerging. The most significant discoveries in our understanding of the structure and function of the glomerular filtration barrier are reviewed in this paper.

Hereditary kidney diseases: highlighting the importance of classical Mendelian phenotypes

A Mendelian inheritance underlies a nonnegligible proportion of hereditary kidney diseases, suggesting that the encoded proteins are essential for maintenance of the renal function. The identification of genes involved in congenital anomalies of the kidney and in familial forms of nephrotic syndrome significantly increased our understanding of the renal development and kidney filtration barrier physiology. This review will focus on the classical phenotype and clinical heterogeneity observed in the monogenic forms of these disorders. In addition, the role of susceptibility genes in kidney diseases with a complex inheritance will also be discussed.

Genetics of nephrotic syndrome: connecting molecular genetics to podocyte physiology

Urinary losses of macromolecules in nephrotic syndrome (NS) reflect a dysfunction of the highly permselective glomerular filtration barrier. Genetic studies of hereditary forms of NS have led to the identification of proteins playing a crucial role in slit-diaphragm signalling, regulation of actin cytoskeleton dynamics, maintenance of podocyte integrity and cell-matrix interactions. This review will focus on recent molecular and clinical findings in the field of genetics of NS, thereby providing a better understanding of the complex glomerular filtration barrier physiology.

Familial nephropathy and multiple exostoses with exostosin-1 (EXT1) gene mutation

Glomerular deposition of fibrillar collagen is a characteristic finding of genetically distinct conditions, including nail-patella syndrome and collagen type III glomerulopathy. A case of familial nephropathy in which steroid-sensitive nephrotic syndrome and glomerular deposits of fibrillar collagen are associated with multiple exostoses due to mutation of the EXT1 gene is described. This gene encodes a glycosyltransferase required for synthesis of heparan sulfate glycosaminoglycans. There is deficiency of heparan sulfate and perlecan, together with accumulation of collagens, in the matrix of EXT1-associated osteochondromas. Similar glomerular basement membrane abnormalities could offer an explanation for both the renal ultrastructural changes and steroid-sensitive nephrotic syndrome.