Use of genomic and functional analysis to characterize patients with steroid-resistant nephrotic syndrome
Children with genetic causes of steroid-resistant nephrotic syndrome (SRNS) usually do well after renal transplantation, while some with idiopathic SRNS show recurrence due to a putative podocyte-toxic factor. Distinguishing different forms of SRNS based on clinical criteria has been difficult. The aim of our study was to test a novel approach that allows categorization of patients into clinically useful subgroups.
Seventeen patients with clinically confirmed SRNS were analyzed by next-generation sequencing (NGS) of 37 known SRNS genes and a functional assay of cultured human podocytes, which indirectly tests for toxicity of patients’ sera by evidenced loss of podocyte focal adhesion complex (FAC) number.
We identified a pathogenic mutation in seven patients (41%). Sera from patients with monogenic SRNS caused mild loss of FAC number down to 73% compared to untreated controls, while sera from seven of the remaining ten patients with idiopathic SRNS caused significant FAC number loss to 43% (non-overlapping difference 30%, 95% CI 26–36%, P < 0.001). All patients with recurrent SRNS (n = 4) in the graft showed absence of podocyte gene mutations but significant FAC loss. Three patients had no mutation nor serum podocyte toxicity.
Our approach allowed categorization of patients into three subgroups: (1) patients with monogenic SRNS; (2) patients with idiopathic SRNS and marked serum podocyte toxicity; and (3) patients without identifiable genetic cause nor evidence of serum podocyte toxicity. Post-transplant SRNS recurrence risk appears to be low in groups 1 and 3, but high in group 2.
KeywordsFocal segmental glomerulosclerosis Steroid-resistant nephrotic syndrome Recurrent FSGS Next-generation sequencing Functional podocyte assay
We thank all patients and their families at the Montreal Children’s Hospital and McMaster Children’s Hospital. We would also like to thank Dr. Vladimir Belostotsky who helped with recruitment and sample collection. Finally, we thank Dr. Moin Saleem for the gift of the human podocyte cell line.
This project received funds from the Pilot Project Competition of the Montreal Children’s Hospital Research Institute.
Compliance with ethical standards
This was a retrospective study in patients with established SRNS/FSGS and was approved by the local institutional review board. Informed consent was obtained from each participant or, where appropriate, the participant’s parents.
All procedures performed involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Conflict of interest
The authors declare that they have no conflicts of interest.
Informed consent was obtained from all individual participants included in the study.
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