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Rituximab has been used over the last decade as a rescue therapy for refractory cases of nephrotic syndrome (NS). Here we report the use of rituximab in four children with idiopathic steroid-resistant nephrotic syndrome (SRNS) with various histological backgrounds (two cases with focal segmental glomerulosclerosis, one case with IgM nephropathy, and one case with minimal change disease), who failed to respond to other immunsuppressions. Their median age (range) was 10 (8-11) years. NPHS2 genetic mutation was negative in all of them. All patients received a single dose of rituximab (375 mg/m(2)) and achieved complete B cell depletion as CD19 was <1% for 3 months following rituximab infusion. Only one patient achieved non-sustained remission as he relapsed after 4 months despite zero CD19 level. Patients received no further doses of rituximab as B cell was depleted in the peripheral circulation. We conclude that a single dose of rituximab was not effective in inducing sustained remission in children with idiopathic SRNS, despite complete B cell depletion in the peripheral circulation. Further doses might be indicated to deplete non-circulating B cells.

A targeted customized sequencing of genes implicated in autosomal recessive polycystic kidney disease (ARPKD) phenotype was performed to identify candidate variants using the Ion torrent PGM next-generation sequencing. The results identified four potential pathogenic variants in PKHD1 gene [c.4870C > T, p.(Arg1624Trp), c.5725C > T, p.(Arg1909Trp), c.1736C > T, p.(Thr579Met) and c.10628T > G, p.(Leu3543Trp)] among 12 out of 18 samples. However, one variant c.4870C > T, p.(Arg1624Trp) was common among eight patients. Some patient samples also showed few variants in autosomal dominant polycystic kidney disease (ADPKD) disease causing genes PKD1 and PKD2 such as c.12433G > A, p.(Val4145Ile) and c.1445T > G, p.(Phe482Cys), respectively. All causative variants were validated by capillary sequencing and confirmed the presence of a novel homozygous variant c.10628T > G, p.(Leu3543Trp) in a male proband. We have recently published the results of these studies (Edrees et al., 2016). Here we report for the first time the effect of the common mutation p.(Arg1624Trp) found in eight samples on the protein structure and function due to the specific amino acid changes of PKHD1 protein using molecular dynamics simulations. The computational approaches provide tool predict the phenotypic effect of variant on the structure and function of the altered protein. The structural analysis with the common mutation p.(Arg1624Trp) in the native and mutant modeled protein were also studied for solvent accessibility, secondary structure and stabilizing residues to find out the stability of the protein between wild type and mutant forms. Furthermore, comparative genomics and evolutionary analyses of variants observed in PKHD1, PKD1, and PKD2 genes were also performed in some mammalian species including human to understand the complexity of genomes among closely related mammalian species. Taken together, the results revealed that the evolutionary comparative analyses and characterization of PKHD1, PKD1, and PKD2 genes among various related and unrelated mammalian species will provide important insights into their evolutionary process and understanding for further disease characterization and management.

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