HIGH-SENSITIVITY ANTI-NEPHRIN AUTOANTIBODY ASSAY PREDICTS STEROID RESISTANCE AND GLOMERULONEPHRITIS IN CHILDHOOD IDIOPATHIC NEPHROTIC SYNDROME

Although several studies have reported the involvement of anti-nephrin autoantibodies in nephrotic syndrome (NS), their clinical significance and association with disease course remain insufficiently understood. In this study, circulating anti-nephrin autoantibodies were measured before prednisolone (PSL) administration in children with newly diagnosed NS using an automated high-sensitivity immunoassay.

From July 2024 to June 2025, children diagnosed with idiopathic NS across Japan were prospectively enrolled, and blood samples were collected before the initiation of PSL therapy. Circulating anti-nephrin autoantibodies were measured using an automated immunoassay on the Automated Immunoassay System HISCL-5000 (Sysmex), which employed the extracellular domain of nephrin recombinantly expressed on human cell lines, with specific mutations introduced to enhance immunocapture sensitivity. Detection was achieved using an ALP-fused anti-human IgG antibody and chemiluminescence. The cutoff value for positivity was determined >807 SU/mL based on acute non-kidney disease controls; samples with antibody levels ≥10,000 SU/mL were defined as high-titer positive. Patients who achieved complete remission within 4 weeks after PSL administration were classified as having steroid-sensitive nephrotic syndrome (SSNS), those who did not achieve remission within 4 weeks were classified as steroid-resistant nephrotic syndrome (SRNS), and those later diagnosed with other forms of glomerulonephritis such as IgA nephropathy during their clinical course were categorized as the glomerulonephritis (GN) group. Continuous variables were expressed as median (interquartile range). Categorical variables were compared using the chi-square test, and continuous variables were compared using the Kruskal–Wallis test and post-hoc pairwise comparisons were performed using the Steel–Dwass test. Statistical significance was defined as P < 0.05.

A total of 63 patients (male 45, female 18, month age 70.5(34.5-141)) with newly diagnosed idiopathic NS were enrolled. The outcomes of SSNS, SRNS, and GN were as follows: positive group (n = 51; 50 SSNS, 1 SRNS, 0 GN), high-titer positive group (n = 6; 1 SSNS, 5 SRNS, 0 GN), and negative group (n = 7; 0 SSNS, 3 SRNS, 4 GN). Patients with high-titer positivity or negativity showed a significantly higher likelihood of developing SRNS or GN compared with those in the positive group (P < 0.0001). There were no significant differences among the three groups in age at onset, serum albumin, serum IgG, serum creatinine, urine protein-to-creatinine ratio, or presence of hematuria. However, the high-titer positive group showed significantly higher serum BUN levels compared with the positive group (P = 0.01).

In all SSNS cases, anti-nephrin autoantibodies were positive, indicating a strong involvement in disease pathogenesis. In cases that progressed to SRNS despite being negative for anti-nephrin autoantibodies, non-immunological mechanisms or other immunological pathways independent of anti-nephrin antibodies were considered to be involved. In patients with high-titer positivity, some showed delayed remission induction, while others with persistently elevated antibody levels failed to achieve remission.

In children with newly diagnosed idiopathic NS, measurement of anti-nephrin autoantibodies using a high-sensitivity immunoassay enables prediction of progression to SRNS or the possibility of GN in cases with negative or high-titer positive results, demonstrating substantial clinical utility. Incorporating anti-nephrin autoantibody profiling into the initial diagnostic workup may therefore contribute to early risk stratification and personalized treatment strategies in pediatric NS.