A novel NPHS2 mutation (c.865A > G) identified in a Chinese family with steroid-resistant nephrotic syndrome alters subcellular localization of nephrin.

backgroundNPHS2 is the causative gene of nephrotic syndrome type 2 (MIM 600995) which often clinically manifests as steroid-resistant nephrotic syndrome (SRNS). The NPHS2 gene encodes a slit diaphragm (SD) associated protein podocin.

objectiveThis study reported a novel disease-causing mutation of NPHS2 in a Chinese family with SRNS. We also investigated the pathogenic mechanism of the variants in this family.

methodA Chinese family with SRNS was recruited. Whole exome sequencing was performed to screen for disease-causing mutation. Sanger sequencing was used to confirm the results. In vitro functional experiments including immunoblotting, co-immunoprecipitation and double immunofluorescence staining were performed to explore the pathogenic mechanisms of mutations.

resultsIn this family, compound heterozygous mutations of NPHS2 (c.467dupT and c.865A > G) were identified and segregated with the disease. The maternal c.865A > G was a novel variant, leading to amino acid substitution (p.K289E). In vitro functional assays indicated that c.467dupT (p.L156FfsX11) mutant lost interaction with nephrin. Both K289E and L156FfsX11 mutants showed sharply diminished plasma membrane localization. Furthermore, abnormal distribution of podocin mutants also altered the cell membrane localization of nephrin.

conclusionWe reported a family with SRNS caused by compound heterozygous mutations of NPHS2 (c.467dupT and c.865A > G). c.865A > G (p.K289E) in NPHS2 was a novel causative variant associated with SRNS. Both variants in this family not only affected the normal cell membrane localization of podocin, but also altered the cell membrane localization of nephrin which is the major architectural protein of SD.