Effective calcineurin inhibitor treatment in adult-onset steroid-resistant nephrotic syndrome with a novel splice donor site variant of TRPC6: a case report.

Transient receptor potential canonical 6 (TRPC6) variants, which were initially detected in adult-onset familial focal segmental glomerulosclerosis (FSGS), were also identified in pediatric-onset one. Here, we present a patient with adult-onset steroid-resistant nephrotic syndrome (SRNS) who harbored a likely pathogenic TRPC6 variant and partially responded to calcineurin inhibitors (CNIs). A 44-year-old woman with stable rheumatoid arthritis, systemic lupus erythematosus, and Sjögren's syndrome was presented with nephrotic syndrome. Her renal biopsy results showed minor glomerular abnormalities. Upon admission, she was treated with steroids for around 4 weeks, but it was ineffective. After 1-2 weeks of cyclosporine A (CyA) administration, urine output increased, renal function improved without a decrease in proteinuria, and she was discharged. Her renal function was maintained for 2 months, but after a CyA dose reduction, she was again admitted to the hospital due to relapsing edema, decreased urine output, and worsening renal function. CyA was replaced by tacrolimus (TAC). A second renal biopsy showed nearly the same findings as the first except for tubulointerstitial lesions. After 1-2 weeks of TAC administration, urine output increased, and renal function improved. However, urinary protein levels did not decrease as before. After discharge, a whole exome analysis revealed a heterozygous splice donor site variant NM_004621.6;c.2644 + 1G > A in TRPC6. Genetic testing identified a novel splice donor site variant of TRPC6 in a patient with adult-onset SRNS, which prevented unnecessary steroid continuation. The safety and efficacy of CNI in TRPC6 glomerulopathy must be evaluated in future larger studies with longer follow-up.