Targeted sequencing experiments for rare disease alleles: implications in clinical practice and diagnosis of steroid-resistant nephrotic syndrome

During recent years, several podocyte genes have been implicated in severe forms of steroid-resistant nephrotic syndrome (SRNS) progressing to renal failure. To date, at least 15 genes highly expressed in the podocyte have been associated with the syndrome and different mutations in these genes have been identified; it is now known that the phenotypes associated with mutations in these genes display significant variability, rendering genetic testing and counselling a more complex task. Traditional methods for sequencing genes are often laborious and not easily available and a screening technique that enables the rapid detection of the pathogenetic variants would be very helpful in the clinical practice. The scope of our work is to apply nextgeneration sequencing (NGS) technology to study patients affected by SRNS, in which the previous analysis of NPHS2 and WT1 genes had not shown any mutations. We perform in 8 affected subjects a targeted resequencing of 46 genes including those already known as causative of the disorder and several other genes highly expressed in the podocyte. We found new heterozygous missense mutations in different genes that occasionally are associated with the disease in childhood (PLCE1, ACTN4, MYO1E, PODXL). We also detected a variation in the ZHX2 gene, to date never associated with SRNS. This gene encode for a transcriptional factor which regulates the expression of several genes in the podocyte, including WT1. This results and further clinical investigations provides an exciting opportunity to reveal more insight into the pathogenic mechanisms that underlie this debilitating disorder.