SCREENING OF MUTATIONS IN THE NPHS2 GENE IN GREEK PATIENTS WITH AUTOSOMAL-RECESSIVE STEROID-RESISTANT NEPHROTIC SYNDROME

INTRODUCTION: Mutations in the NPHS2 gene, encoding podocin, are a major cause of autosomal-recessive steroid-resistant nephrotic syndrome (SRNS) in childhood and have been observed in 6.4% to 30% of sporadic and 20% to 40% of familial cases. OBJECTIVE: We investigated mutations in the coding region of the NPHS2 gene in Greek patients with SRNS and identified a novel A295T mutation. METHODS: The study included 16 child patients with SRNS (14 families); 11 cases were sporadic, and 5 (from 3 families) were familial. All 8 exons of NPHS2 , including intron boundaries, were screened for sequence variations by using denaturing gradient gel electrophoresis followed by specific characterization using direct DNA sequencing. RESULTS: The results revealed 2 pathogenic genotypes in 2 patients with sporadic SRNS (R138Q/R138Q and R229Q/A295T). In addition, 3 previously described NPHS2 intronic polymorphisms (IVS3–46C→T, IVS3–21C→T, and IVS7+7A→G), 1 thus-far-unreported intronic variant (IVS3–17C→T), and 4 known silent mutations (G34G, S96S, A318A, and L346L) were detected in sporadic and familial cases as well as in healthy controls. CONCLUSIONS: These findings indicate that NPHS2 mutations are not a frequent cause of familial SRNS in Greek patients. Among patients with sporadic SRNS, the genotypes R138Q/R138Q and R229Q/A295T account for an allelic frequency of 18.2%. The R138Q mutation is well characterized. The novel mutation, A295T (883G→A), is predicted in silico to cause a structural alteration in the cytoplasmic domain of podocin (see the PolyPhen database at http://genetics.bwh.harvard.edu/pph). This is the first report of NPHS2 mutations in the Greek population and the first description of the A295T amino acid substitution.