Simultaneous sequencing of 24 genes associated with steroid-resistant nephrotic syndrome

Abstract

Background and objectives: Up to 95% of children presenting with steroid-resistant nephrotic syndrome in early life will have a pathogenic single-gene mutation in 1 of 24 genes currently associated with this disease. Others may be affected by polymorphic variants. There is currently no accepted diagnostic algorithm for clinical genetic testing. The hypothesis was that the increasing reliability of next generation sequencing allows comprehensive one-step genetic investigation of this group and similar patient groups.

Design, setting, participants, & measurements: This study used next generation sequencing to screen 446 genes, including the 24 genes known to be associated with hereditary steroid-resistant nephrotic syndrome. The first 36 pediatric patients collected through a national United Kingdom Renal Registry were chosen with comprehensive phenotypic detail. Significant variants detected by next generation sequencing were confirmed by conventional Sanger sequencing.

Results: Analysis revealed known and novel disease-associated variations in expected genes such as NPHS1, NPHS2, and PLCe1 in 19% of patients. Phenotypically unexpected mutations were also detected in COQ2 and COL4A4 in two patients with isolated nephropathy and associated sensorineural deafness, respectively. The presence of an additional heterozygous polymorphism in WT1 in a patient with NPHS1 mutation was associated with earlier-onset disease, supporting modification of phenotype through genetic epistasis.

Conclusions: This study shows that next generation sequencing analysis of pediatric steroid-resistant nephrotic syndrome patients is accurate and revealing. This analysis should be considered part of the routine genetic workup of diseases such as childhood steroid-resistant nephrotic syndrome, where the chance of genetic mutation is high but requires sequencing of multiple genes.

Figure 1.

Flow diagram showing mechanism for filtering variants to identify those variants of potential pathogenicity.

Figure 2.

Comparison of NGS and Sanger sequencing data acquisition Sequencing results for patient 8 and parents in gene COQ2 at nucleotide position c.683A>G (N228S; A, C, E, and G) and nucleotide position c.701delT (L234fsX247; B, D, F, and H). Next generation sequencing showed a heterozygous ns single-nucleotide polymorphism (SNP; A) and a heterozygous deletion (B) in patient 8. Both the non-synonymous (ns) SNP (C) and the deletion (D) were confirmed by Sanger methodology. The mother of the patient was confirmed to be a heterozygous carrier of the nsSNP (E) but not the deletion (F), whereas father did not carry the nsSNP (G) but was found to be heterozygous for the deletion (H).