Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of chronic kidney disease in children and young adults. The most severe form of steroid-resistant nephrotic syndrome is congenital nephrotic syndrome Finnish type (CNSF), caused by biallelic loss-of-function variants in NPHS1, encoding nephrin. Since each of the 68 monogenic causes of steroid-resistant nephrotic syndrome represents a rare cause of the disease, tailoring therapeutic interventions to multiple molecular targets remains challenging, suggesting gene replacement therapy (GRT) as a viable alternative. To set the ground for a gene replacement study in vivo, we established rigorous, quantifiable, and reproducible phenotypic assessment of a conditional Nphs1 knockout mouse model. By breeding a floxed Nphs1fl/- mouse (Nphs1tm1Afrn/J) previously studied for pancreatic β-cell survival with a podocin promoter-driven Cre recombinase mouse model (Tg(NPHS2-Cre)295Lbh/J), we generated mice with podocyte-specific nephrin deficiency (Nphs1fl/fl NPHS2-Cre +). We observed a median survival to postnatal day P5 in nephrin-deficient mice, whereas heterozygous control mice and wild type (WT) control group showed 90% and 100% survival, respectively (at P50 days). Light microscopy analysis showed a significantly higher number of renal-tubular microcysts per kidney section in nephrin-deficient mice compared to the control groups (P < 0.0022). Transmission electron microscopy demonstrated reduced foot process (FP) density in nephrin-deficient mice compared to controls (P < 0.0001). Additionally, proteinuria quantitation using urine albumin-to-creatinine ratio (UACR) was significantly higher in nephrin-deficient mice compared to controls. This study represents the first comprehensive description of the kidney phenotype in a nephrin-deficient mouse model, laying the foundation for future gene replacement therapy endeavors.

A 5 +-day-old male patient was hospitalized due to a significant increase of urine protein for 5 + d. A 36 +4 weeks preterm male infant was found with III° polluted amniotic fluid and excessive placenta, presented with proteinuria, hypoproteinemia, and progressive edema after birth. Two heterozygous mutations of NPHS1 gene, c.3325C>T (p.Arg1109*) and c.2479C>T (p.Arg827*), were found through the whole exon gene detection. The latter has not been reported domestically and the diagnosis of congenitalnephrotic syndrome of the Finnish type (CNF) is definite. The report of c.2479C>T mutation gene will expand the mutation spectrum of CNF gene data in China. Early genetic testing is recommended for cryptogenic congenital nephrotic syndrome (CNS) and early genetic diagnosis of CNF is important for prognostic evaluation, genetic counseling and clinical management.

Identification of the NPHS1 gene, which encodes nephrin, was followed by many studies demonstrating its mutation as a frequent cause of congenital nephrotic syndrome (CNS). While this gene is found in 98% of Finnish children with this syndrome, non-Finnish cases have lower level of incidence ranging from 39 to 80%. This report describes the clinical presentation of a two-week-old neonate who presented with periorbital and lower extremities edema, abdominal distention, heavy proteinuria, serum hypoproteinemia and failure to thrive. Genetic analysis revealed NHPS1 gene mutation leading to CNS-Finnish type diagnosis. Through this case we want to create awareness about diagnosis and treatment challenges in developing countries for rare congenital diseases.

We report five fetuses and a child from three families who shared a phenotype comprising cerebral ventriculomegaly and echogenic kidneys with histopathological findings of congenital nephrosis. The presenting features were greatly elevated maternal serum alpha-fetoprotein (MSAFP) or amniotic fluid alpha-fetoprotein (AFAFP) levels or abnormalities visualized on ultrasound scan during the second trimester of pregnancy. Exome sequencing revealed deleterious sequence variants in Crumbs, Drosophila, Homolog of, 2 (CRB2) consistent with autosomal-recessive inheritance. Two fetuses with cerebral ventriculomegaly and renal microcysts were compound heterozygotes for p.Asn800Lys and p.Trp759Ter, one fetus with renal microcysts was a compound heterozygote for p.Glu643Ala and p.Asn800Lys, and one child with cerebral ventriculomegaly, periventricular heterotopias, echogenic kidneys, and renal failure was homozygous for p.Arg633Trp in CRB2. Examination of the kidneys in one fetus showed tubular cysts at the corticomedullary junction and diffuse effacement of the epithelial foot processes and microvillous transformation of the renal podocytes, findings that were similar to those reported in congenital nephrotic syndrome, Finnish type, that is caused by mutations in nephrin (NPHS1). Loss of function for crb2b and nphs1 in Danio rerio were previously shown to result in loss of the slit diaphragms of the podocytes, leading to the hypothesis that nephrosis develops from an inability to develop a functional glomerular barrier. We conclude that the phenotype associated with CRB2 mutations is pleiotropic and that the condition is an important consideration in the evaluation of high MSAFP/AFAFP where a renal cause is suspected.