Identification of monogenic variants in steroid-resistant and steroid-sensitive nephrotic syndrome

Background: Steroid-resistant nephrotic syndrome (SRNS) constitutes the second most common cause of chronic kidney disease (CKD) in children. A monogenic cause can be identified in approximately 25% of SRNS cases. In contrast, steroid-sensitive or steroid-dependent nephrotic syndrome (SSNS/SDNS) is typically attributed to multifactorial or immunological causes and rarely linked to monogenic etiology. Methods: We performed exome sequencing (ES) in 237 families, including 183 with SRNS and 54 with SSNS/SDNS. Results: A (likely) pathogenic variant in a known SRNS gene was identified in 29/183 individuals with SRNS (15.8%). Additionally, 6/183 (3.3%) individuals with SRNS carried pathogenic variants in phenocopy genes—genes associated with diseases that clinically mimic SRNS. The diagnostic yield was significantly higher in individuals with ≥ 50 Mb homozygosity-by-descent (HBD) (44.7% vs. 8.5%) and in those with SRNS disease onset before 1 year of age (41.9%). In individuals with SSNS/SDNS, we found a likely causative variant in only 1 of 54 probands. Conclusions: A genetic cause was established in 19.1% of SRNS patients (15.8% in known SRNS genes and 3.3% in phenocopy genes), but only 1.9% of non-steroid-resistant cases.