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 Sj & ouml;gren'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.