Analysis of NPHS2 Gene Mutations in Egyptian Children with Nephrotic Syndrome

Abstract

Background: Mutations in the NPHS2 genes are the main aetiology of early-onset and familial steroid-resistant nephrotic syndrome (SRNS). The pathogenic NPHS2 mutation together with the p.R229Q variant has been less described among Egyptian children.

Aim: This study aims to determine the mutation of NPHS2 in children with NS and discover the role of p.R229Q variant in SRNS.

Methods: The study included 53 children with NS, and 53 healthy volunteers matched in age and sex controls. The median age at disease onset was 7.3 years. Among NS cases, 31 cases had steroid-sensitive nephrotic syndrome (SSNS) and 22 children with steroid-resistant nephrotic syndrome (SRNS). Polymerase chain reaction amplification of the whole coding region of NPHS2 gene was carried out for its mutational analysis. Restriction digestion testing was carried out after PCR to determine the presence of R229Q polymorphism. Randomly selected samples were re-genotyped by two independent technicians for assessment of Quality control.

Results: NS patients showed a significant higher frequency of heterozygous genotype GA (89.5%) compared to control group (10.5%) with increased risk of NS (OR, 12.04; 95% CI, 2.61 to55.38; p < 0.0001). Moreover, SRNS showed a significant higher frequency of GA genotype (68.2%) than the SSNS group (6.5%). The GA genotype was associated with increased risk of SRNS (OR, 31.1; 95% CI, 5.73 to 168.48; P < 0.001) and the A allele was associated with increased risk of SRNS (OR, 15.52; 95% CI, 3.325 to 72.422; P < .001).

Conclusion: R229Q polymorphisms are associated with SRNS, and any child with SRNS should be searched for mutations in the NPHS2 gene.

Keywords: NPHS2 mutation; R229Q polymorphism; Steroid resistant nephrotic syndrome.

Figure 1

Amplified PCR products in 6 healthy subjects (left); Agarose gel stained with ethidium bromide illustrating PCR product of exon 5 of NPHS2 gene before and after digestion with ClaI endonuclease enzyme for patients and healthy controls with wild genotype (GG) of R229Q and for one patient with the heterozygote genotype (GA) of R229Q (right)

Figure 2

Sequence chromatogram of exon 5 of NPHS2 gene showing wild pattern (p.Arg 229Gln) (c.686G > A). Site is denoted by the arrow (left); Sequence chromatogram of exon 5 of NPHS2 gene showing heterozygous pattern (p.Arg229 Gln) (c.686G > A). Site of mutation is denoted by the arrow (right)