mRNA sequencing of a novel NPHS2 intronic mutation in a child with focal and segmental glomerulosclerosis.

The NPHS2 gene encodes podocin, a membrane protein that acts as the structural scaffold in podocyte foot processes. NPHS2 mutations are associated with steroid-resistant nephrotic syndrome (SRNS), with the pathologic variant being focal and segmental glomerulosclerosis (FSGS), an emerging cause of end-stage renal disease in children. We describe a novel NPHS2 sequence variant in a girl with SRNS. Onset occurred at the age of seven years, with edema, hypo-proteinemia, hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia and nephrotic proteinuria. Renal function was normal and autoimmunity markers were negative. Proteinuria failed to decrease after standard steroid therapy. Renal biopsy showed FSGS. Cyclosporine therapy was instituted, but no remission of proteinuria was achieved and chronic renal failure developed. Molecular analysis of the NPHS2 gene revealed a homozygous nucleotide substitution in position c.451+3A>T in intron 3-4. This nucleotide substitution has not been reported in the literature till date. The effect of the detected substitution on podocin protein was demonstrated by renal biopsy RNA extraction and cDNA amplification analysis. This technique had never been applied to a NPHS2 mutation. Based on these results, immunosuppressive drugs were discontinued and conservative therapy was undertaken.