NPHS2 V260E Is a Frequent Cause of Steroid-Resistant Nephrotic Syndrome in Black South African Children

Hiding in plain sight: genetics of childhood steroid-resistant nephrotic syndrome in Sub-Saharan Africa

Steroid-resistant nephrotic syndrome (SRNS) is the most severe form of childhood nephrotic syndrome with an increased risk of progression to chronic kidney disease stage 5. Research endeavors to date have identified more than 80 genes that are associated with SRNS. Most of these genes regulate the structure and function of the podocyte, the visceral epithelial cells of the glomerulus. Although individuals of African ancestry have the highest prevalence of SRNS, especially those from Sub-Saharan Africa (SSA), with rates as high as 30-40% of all cases of nephrotic syndrome, studies focusing on the characterization and understanding of the genetic basis of SRNS in the region are negligible compared with Europe and North America. Therefore, it remains unclear if some of the variants in SRNS genes that are deemed pathogenic for SRNS are truly disease causing, and if the leading causes of monogenic nephrotic syndrome in other populations are the same for children in SSA with SRNS. Other implications of this lack of genetic data for SRNS in the region include the exclusion of children from the region from clinical trials aimed at identifying potential novel therapeutic agents for this severe form of nephrotic syndrome. This review underlines a need for concerted efforts to advance the genetic basis of SRNS in children in SSA. Such endeavors will complement global efforts at understanding the genetic basis of nephrotic syndrome.

Genetic stratification reveals COL4A variants and spontaneous remission in Egyptian children with proteinuria in the first 2 years of life

AIM

The earlier the onset of proteinuria, the higher the incidence of genetic forms. Therefore, we aimed to analyse the spectrum of monogenic proteinuria in Egyptian children presenting at age <2 years.

METHODS

The results of 27-gene panel or whole-exome sequencing were correlated with phenotype and treatment outcomes in 54 patients from 45 families.

RESULTS

Disease-causing variants were identified in 29/45 (64.4%) families. Mutations often occurred in three podocytopathy genes: NPHS1, NPHS2 and PLCE1 (19 families). Some showed extrarenal manifestations. Additionally, mutations were detected in 10 other genes, including novel variants of OSGEP, SGPL1 and SYNPO2. COL4A variants phenocopied isolated steroid-resistant nephrotic syndrome (2/29 families, 6.9%). NPHS2 M1L was the single most common genetic finding beyond the age of 3 months (4/18 families, 22.2%). Biopsy results did not correlate with genotypes (n = 30). On renin-angiotensin-aldosterone system antagonists alone, partial and complete remission occurred in 3/24 (12.5%) patients with monogenic proteinuria each, whereas 6.3% (1/16) achieved complete remission on immunosuppression.

CONCLUSION

Genotyping is mandatory to avoid biopsies and immunosuppression when proteinuria presents at age <2 years. Even with such a presentation, COL4A genes should be included. NPHS2 M1L was prevalent in Egyptian children (4 months-2 years) with proteinuria, demonstrating precision diagnostic utility.

Childhood Nephrotic Syndrome in Africa: Epidemiology, Treatment Trends, and Outcomes

Nephrotic syndrome is a common childhood glomerular disease that is associated with massive proteinuria and edema. Children with nephrotic syndrome are at risk of chronic kidney disease, disease-related complications, and treatment-related complications. Patients with frequently relapsing disease or steroid toxicity may require newer immunosuppressive medications. However, access to these medications is limited in many African countries owing to prohibitive cost, the need for frequent therapeutic drug monitoring, and a lack of appropriate facilities. This narrative review examines the epidemiology of childhood nephrotic syndrome in Africa, including trends in treatment and patient outcomes. In most of North Africa, as well as among White and Indian populations in South Africa, the epidemiology and treatment of childhood nephrotic syndrome closely resembles that of European and North American populations. Historically, secondary causes of nephrotic syndrome (eg, quartan malaria nephropathy and hepatitis B-associated nephropathy) were predominant among Blacks in Africa. Over time, the proportion of secondary cases has decreased, along with rates of steroid resistance. However, focal segmental glomerulosclerosis increasingly has been reported among patients with steroid resistance. There is a need for consensus guidelines for the management of childhood nephrotic syndrome in Africa. Furthermore, establishing an African nephrotic syndrome registry could facilitate monitoring of disease and treatment trends, and provide opportunities for advocacy and research to improve patient outcomes.

Causal and putative pathogenic mutations identified in 39% of children with primary steroid-resistant nephrotic syndrome in South Africa

There is a paucity of data identifying genetic mutations that account for the high rate of steroid-resistant nephrotic syndrome (SRNS) in a South African paediatric population. The aim was to identify causal mutations in genes implicated in SRNS within a South African paediatric population. We enrolled 118 children with primary nephrotic syndrome (NS), 70 SRNS and 48 steroid-sensitive NS. All children with SRNS underwent kidney biopsy. We first genotyped the NPHS2 gene for the p.V260E variant in all NS cases (n = 118) and controls (n = 219). To further identify additional variants, we performed whole-exome sequencing and interrogated ten genes (NPHS1, NPHS2, WT1, LAMB2, ACTN4, TRPC6, INF2, CD2AP, PLCE1, MYO1E) implicated in SRNS with histopathological features of focal segmental glomerulosclerosis (FSGS) in 56 SRNS cases and 29 controls; we also performed exome sequencing on two patients carrying the NPHS2 p.V260E mutation as positive controls. The overall detection rate of causal and putative pathogenic mutations in children with SRNS was 27/70 (39%): 15 (21%) carried the NPHS2 p.V260E causal mutation in the homozygous state, and 12 (17%) SRNS cases carried a putative pathogenic mutation in the heterozygous state in genes (INF2 (n = 8), CD2AP (n = 3) and TRPC6 (n = 1)) known to have autosomal dominant inheritance mode. NPHS2 p.V260E homozygosity was specifically associated with biopsy-proven FSGS, accounting for 24% of children of Black ethnicity (15 of 63) with steroid-resistant FSGS. No causal or putative pathogenic mutations were identified in NPHS1, WT1, LAMB2, PLCE1, MYO1E and ACTN4. We report four novel variants in INF2, PLCE1, ACTN4 and TRPC6.   Conclusion: We report putative missense variants predicted to be pathogenic in INF2, CD2AP and TRPC6 among steroid-resistant-FSGS children. However, the NPHS2 p.V260E mutation is a prevalent cause of steroid-resistant FSGS among Black South African children occurring in 24% of children with SRNS. Screening all Black African children presenting with NS for NPHS2 p.V260E will provide a precision diagnosis of steroid-resistant FSGS and inform clinical management. What is Known: • Limited data is available on the genetic disparity of SNRS in a South African paediatric setting. • The high rate of steroid resistance in Black South African children with FSGS compared to other racial groups is partially explained by the founder variant NPHS2 p.V260E. What is New: • We report putative missense variants predicted to be pathogenic in INF2, CD2AP and TRPC6 among steroid-resistant FSGS children. • NPHS2 p.V260E mutation remains a prevalent cause of steroid-resistant FSGS among Black South African children, demonstrating precision diagnostic utility.

The association of NPHS1 and ACNT4 gene polymorphisms with pre-eclampsia

OBJECTIVE

The main objective of this study is to investigate the association of the NPHS1 gene polymorphisms (rs437168) and ACTN4 (rs3745895) in the pathogenesis of PE in women of African Ancestry.

MATERIALS AND METHODS

637 blood samples, normotensive pregnant (n = 280) and pre-eclampsia (n = 357) were included. The PE group was sub-divided into early onset pre-eclampsia (n = 187) and late onset pre-eclampsia (n = 170). rs74315346, rs869025495, rs121908415, rs3745895, and rs437168 were genotyped from isolated DNA using real time PCR.

RESULTS

The C allele of rs437168 (NPHS1) was significantly higher in PE compared to controls. [C vs T; p = 0.0323*] and [CC vs CT/TT; p = 0.0464*]. A comparison between the subtypes of PE and controls showed that the C allele was significantly higher in EOPE compared to controls [p = 0.0027^**], [CC vs CT/TT; p = 0.0111*], [CC/CT vs TT p = 0.0198*] and LOPE. [p = 0.0259*]. The other SNPs genotyped showed no signification associations with PE.

CONCLUSION

This study found that the C allele of rs437168 is significantly associated with the pathogenesis of early onset PE and may be accountable for renal injury, which is a risk factor for the development of EOPE in women of African Ancestry.

Nephrotic syndrome-associated hypercoagulopathy is alleviated by both pioglitazone and glucocorticoid which target two different nuclear receptors

BACKGROUND

Thrombosis is a potentially life-threatening nephrotic syndrome (NS) complication. We have previously demonstrated that hypercoagulopathy is proportional to NS severity in rat models and that pioglitazone (Pio) reduces proteinuria both independently and in combination with methylprednisolone (MP), a glucocorticoid (GC). However, the effect of these treatments on NS-associated hypercoagulopathy remains unknown. We thus sought to determine the ability of Pio and GC to alleviate NS-associated hypercoagulopathy.

METHODS

Puromycin aminonucleoside-induced rat NS was treated with sham, Low- or High-dose MP, Pio, or combination (Pio + Low-MP) and plasma was collected at day 11. Plasma samples were collected from children with steroid-sensitive NS (SSNS) and steroid-resistant NS (SRNS) upon presentation and after 7 weeks of GC therapy. Plasma endogenous thrombin potential (ETP), antithrombin (AT) activity, and albumin (Alb) were measured using thrombin generation, amidolytic, and colorimetric assays, respectively.

RESULTS

In a rat model of NS, both High-MP and Pio improved proteinuria and corrected hypoalbuminemia, ETP and AT activity (p < .05). Proteinuria (p = .005) and hypoalbuminemia (p < .001) were correlated with ETP. In childhood NS, while ETP was not different at presentation, GC therapy improved proteinuria, hypoalbuminemia, and ETP in children with SSNS (p < .001) but not SRNS (p = .330).

CONCLUSIONS

Both Pio and GC diminish proteinuria and significantly alleviate hypercoagulopathy. Both Pio and MP improved hypercoagulopathy in rats, and successful GC therapy (SSNS) also improved hypercoagulopathy in childhood NS. These data suggest that even a partial reduction in proteinuria may reduce NS-associated thrombotic risk.

Regulation of the Actin Cytoskeleton in Podocytes

Podocytes are an integral part of the glomerular filtration barrier, a structure that prevents filtration of large proteins and macromolecules into the urine. Podocyte function is dependent on actin cytoskeleton regulation within the foot processes, structures that link podocytes to the glomerular basement membrane. Actin cytoskeleton dynamics in podocyte foot processes are complex and regulated by multiple proteins and other factors. There are two key signal integration and structural hubs within foot processes that regulate the actin cytoskeleton: the slit diaphragm and focal adhesions. Both modulate actin filament extension as well as foot process mobility. No matter what the initial cause, the final common pathway of podocyte damage is dysregulation of the actin cytoskeleton leading to foot process retraction and proteinuria. Disruption of the actin cytoskeleton can be due to acquired causes or to genetic mutations in key actin regulatory and signaling proteins. Here, we describe the major structural and signaling components that regulate the actin cytoskeleton in podocytes as well as acquired and genetic causes of actin dysregulation.

The podocin V260E mutation predicts steroid resistant nephrotic syndrome in black South African children with focal segmental glomerulosclerosis

In black African children with focal segmental glomerulosclerosis (FSGS) there are high rates of steroid resistance. The aim was to determine genetic associations with apolipoprotein L1 (APOL1) renal risk variants and podocin (NPHS2) variants in 30 unrelated black South African children with FSGS. Three APOL1 variants were genotyped and the exons of the NPHS2 gene sequenced in the cases and controls. APOL1 risk alleles show a modest association with steroid sensitive nephrotic syndrome (SSNS) and steroid resistant nephrotic syndrome (SRNS). The NPHS2 V260E variant was present in SRNS cases (V/V = 5; V/E = 4; E/E = 11), and was absent in SSNS cases. Haplotype analysis suggests a single mutation origin for V260E and it was associated with a decline in kidney function over a 60-month period (p = 0.026). The V260E variant is a good predictor of autosomal recessive SRNS in black South African children and could provide useful information in a clinical setting.

Efficacy and safety of cyclosporine a for patients with steroid-resistant nephrotic syndrome: a meta-analysis

BACKGROUND

The purpose of this study was to determine efficacy and safety of cyclosporine A (CsA) for patients with steroid-resistant nephrotic syndrome (SRNS).

METHODS

The Cochrane Library and PubMed were searched to extract the associated studies on Oct 10, 2018, and the meta-analysis method was used to pool and analyze the applicable investigations included in this study. The P(opulation) I(ntervention) C(omparison) O(utcome) of the study were defined as follows: P: Patients with SRNS; I: treated with CsA, cyclophosphamide (CYC), tacrolimus (TAC) or placebo/not treatment (P/NT); C: CsA vs. placebo/nontreatment (P/NT), CsA vs. CYC, CsA vs. TAC; O: complete remission (CR), total remission (TR; complete or partial remission (PR)), urine erythrocyte number, proteinuria levels, albumin, proteinuria, serum creatinine, and plasma cholesterol, etc. Data were extracted and pooled using RevMan 5.3.

RESULTS

In the therapeutic regimen of CsA vs. placebo/nontreatment (P/NT), the results indicated that the CsA group had high values of CR, TR, and low values of proteinuria, serum creatinine, and plasma cholesterol when compared with those in the placebo group. In comparing CsA vs. cyclophosphamide (CYC), the results indicated that the CsA group had higher TR than the CYC group. In comparing CsA vs. tacrolimus (TAC), the results revealed insignificant differences in CR, and TR between the CsA and TAC groups. The safety of CsA was also assessed. The incidence of gum hyperplasia in CsA group was higher than that in the P/NT group, with no differences in incidence of infections or hypertension between CsA and P/NT groups. There was no difference in the incidence of hypertension between the CsA and TAC groups.

CONCLUSIONS

CsA is an effective and safe agent in the therapy of patients with SRNS.

Nephrotic Syndrome in South African Children: Changing Perspectives in the New Millennium

The epidemiological landscape of nephrotic syndrome (NS) in South Africa has changed drastically in the New Millennium. Although the pattern of disease in the 3 main non-Black racial groups (White, Indian, and Mixed race) mirror that seen in Western countries, Black African children show a pattern of disease that is at variance with these 3 racial groups. The incidence of infectious diseases, particularly hepatitis B virus associated nephropathy has sharply declined to being almost extinct in Black children in the New Millennium whereas HIV-related nephropathy surfaced. However, following the widespread use of anti-retroviral therapy, its incidence has also decreased dramatically. Focal segmental glomerulosclerosis (FSGS), which was once uncommon, has, in the New Millennium, emerged as one of the most challenging forms of NS across all racial groups, particularly in Black children. Although the introduction of calcineurin inhibitors, mycophenolate mofetil and monoclonal antibodies (e.g., rituximab) has improved the outcome of children with FSGS, the reponse in Black children is less than optimal, with those having single gene mutations being universally unresponsive to all forms of immunosuppression.