NPHS2 variation in sporadic focal segmental glomerulosclerosis

Abstract

Mutations in NPHS2, the gene that encodes podocin, are well-established causes of both familial and sporadic steroid-resistant focal segmental glomerulosclerosis (FSGS) in the pediatric population, but have not been well-characterized in late-onset disease. To investigate the role of NPHS2 polymorphisms in sporadic cases of late-onset FSGS, we studied 377 biopsy-confirmed FSGS cases and 919 controls. We identified 18 single nucleotide polymorphisms (SNPs) by resequencing a subgroup of cases and controls, and subsequently genotyped African-American and European-American cases and controls for five missense SNPs, three SNPs within introns, and four SNPs in the 3' untranslated region. No homozygotes or compound heterozygotes were observed for any missense mutation. R138Q carriers were more frequent among FSGS cases relative to controls (OR = 4.9, P = 0.06), but heterozygosity for the other four missense mutations was equally distributed among FSGS cases and controls. Finally, a common haplotype of noncoding SNPs carried by 20% of African-Americans, but not observed in European-Americans, was strongly associated with a 50% reduction in risk for sporadic FSGS (OR = 0.5, P = 0.001). These results indicate that genetic variation or mutation of NPHS2 may play a role in late-onset sporadic FSGS.

Figure 1

(A) Map of NPHS2. Exons are represented by shaded blocks and the 3′ untranslated region by a white block. Exon numbers are above the diagram, and SNP locations are below the diagram. (1) Nucleotide substitution and SNP numbers. (B) Only haplotypes with a frequency >5% in at least one of the groups are presented. Haplotypes were inferred using Phase. Minor alleles are shown in bold. (C) Minor allele frequencies (MAF) in patients with FSGS and control subjects are presented. (D) Haplotype frequencies for AA and EA patients and control subjects. *P < 0.05, **P ≤ 0.002, Fisher exact test.