APOL1 in an ethnically diverse pediatric population with nephrotic syndrome: implications in focal segmental glomerulosclerosis and other diagnoses.

BACKGROUND: APOL1 high-risk genotypes (HRG) are associated with increased risk of kidney disease in individuals of African ancestry. We analyzed the effects of APOL1 risk variants on an ethnically diverse Brazilian pediatric nephrotic syndrome (NS) cohort. METHODS: Multicenter study including 318 NS patients, categorized as progressors to advanced CKD [estimated glomerular filtration rate (eGFR)] < 30 mL/min/1.73 m2] and slow/non-progressors (eGFR > 30 mL/min/1.73 m2 through the study). We employed Cox regression with progression time as the outcome and APOL1 genotype as the independent variable. We tested this association in the entire cohort and three subgroups; (1) focal segmental glomerulosclerosis (FSGS), (2) steroid-resistant NS (SRNS), and (3) those who underwent kidney biopsy. RESULTS: Nineteen patients (6%) had an HRG. Of these, 47% were self-reported White. Patients with HRG manifested NS at older ages and presented higher frequencies of FSGS and SRNS. HRG patients progressed to advanced CKD more often than low-risk-genotype (LRG) children in the whole NS cohort (p = 0.001) and the three subgroups. In SRNS and biopsied patients, a single risk variant was associated with trends of higher CKD progression risk. CONCLUSIONS: Novel discoveries include a substantial prevalence of HRG among patients self-reported White, worse kidney outcomes in HRG versus LRG children in the FSGS subgroup, and a trend of higher CKD progression risk associated with a single risk variant in the SRNS cohort. These findings suggest APOL1-associated NS extends beyond patients self-reported non-White, the HRG effect is independent of FSGS, and a single risk variant may have a detrimental impact in children with NS.

Promises and pitfalls of whole-exome sequencing exemplified by a nephrotic syndrome family.

High-throughput techniques such as whole-exome sequencing (WES) show promise for the identification of candidate genes that underlie Mendelian diseases such as nephrotic syndrome (NS). These techniques have enabled the identification of a proportion of the approximately 54 genes associated with NS. However, the main pitfall of using WES in clinical and research practice is the identification of multiple variants, which hampers interpretation during downstream analysis. One useful strategy is to evaluate the co-inheritance of rare variants in affected family members. Here, we performed WES of a patient with steroid-resistant NS (SRNS) and intermittent microhematuria. Currently, 15 years after kidney transplantation, this patient presents normal kidney function. The patient was found to be homozygous for a rare MYO1E stop-gain variant, and was heterozygous for rare variants in NS-associated genes, COL4A4, KANK1, LAMB2, ANLN, E2F3, and APOL1. We evaluated the presence or absence of these variants in both parents and 11 siblings, three of whom exhibited a milder phenotype of the kidney disease. Analysis of variant segregation in the family, indicated the MYO1E stop-gain variant as the putative causal variant underlying the kidney disease in the patient and two of her affected sisters. Two secondary variants in COL4A4-identified in some other affected family members-require further functional studies to determine whether they play a role in the development of microhematuria in affected family members. Our data illustrate the difficulties in distinguishing the causal pathogenic variants from incidental findings after WES-based variant analysis, especially in heterogenous genetic conditions, such as NS.

NPHS1 gene mutations confirm congenital nephrotic syndrome in four Brazilian cases: A novel mutation is described.

AIM: Autosomal recessive mutations in NPHS1 gene are a common cause of congenital nephrotic syndrome (CNS). The disorder is characterized by massive proteinuria that manifests in utero or in the neonatal period during the first 3 months of life. NPHS1 encodes nephrin, a member of the immunoglobulin family of cell adhesion molecules and the main protein expressed at the renal slit diaphragm. Currently, there are approximately 250 mutations described in the NPHS1 gene distributed among all nephrin domains. The main objective of this study was to perform the analysis of the NPHS1 gene in patients with congenital nephrotic syndrome in order to determine the molecular cause of the disease. METHODS: Direct sequencing of NPHS1 gene in four children was performed. RESULTS: Each patient was heterozygous for two pathogenic mutations disclosing the molecular cause of the disease in 100% of the cases. We identified six different mutations, consisting of one in-frame deletion, one frameshift, and four missense substitutions. The p.Val736Met mutation that is described here for the first time was considered pathogenic by different mutation predictive algorithms. Regardless of the type of mutation, three patients had a bad outcome and died CONCLUSIONS: Despite the small size of the cohort, this study contributed to the increasing number of deleterious mutations in the NPHS1 gene by describing a new mutation. Also, since we identified NPHS1 pathogenic mutations as the cause of the disease in all cases analyzed, it might be a frequent cause of CNS in the South Eastern region of Brazil, although the analysis of a larger sample is required to obtain more indicative epidemiological data.