IgAN with Extracapillary Proliferation in Genetically Identical Twins: Use of Iptacopan

Introduction: IgA nephropathy (IgAN) is the most common primary glomerulonephritis, driven by abnormal IgA1 production, immune complex deposition, and alternative complement pathway activation. Prognostic factors include proteinuria >1 g/day, hypertension, decreased eGFR, and the MEST-C score. Novel therapies targeting the complement system, such as iptacopan - a factor B inhibitor - have shown promising results. Case Description: Case 1: An 18-year-old male was diagnosed with rapidly progressive IgAN. At 16 y.o., he presented microhematuria and urine protein/creatinine ratio (UPCR) 0.5 g/gCr. At 18 y.o., he showed edema, dyspnea, hypertension, UPCR 2.4 g/gCr, and eGFR 27 mL/min/1.73 m2. Renal biopsy revealed extracapillary proliferation (M1E1S1T1C2). Despite treatment with corticosteroids, rituximab, and cyclophosphamide, he progressed to end-stage renal disease, requiring dialysis and transplantation. No monogenic renal disease was identified in >400 analyzed genes, pending exosomes analysis. Case 2: In July 2022, the 18-year-old monozygotic twin presented with UPCR 0.8 g/gCr, microhematuria and eGFR 100 mL/min/1.73 m2. Biopsy showed mesangial, endocapillary, and extracapillary proliferation (26%), 10% fibrosis, and strong IgA and C3 deposits (M1E1S1T0C2), C4d-negative. Despite receiving corticosteroids, cyclophosphamide, and azathioprine, eGFR declined to 82 mL/min/1.73 m2, with UPCR 1 g/g and microhematuria. Azathioprine was switched to mycophenolate, and enteric budesonide and dapagliflozin were added. In Apr 2024, eGFR dropped to 68 mL/min/1.73 m2; second biopsy showed M1E1S1T1C1 with 42% glomerular sclerosis and 40% interstitial fibrosis. Compassionate use of iptacopan (200 mg/12h) was initiated in July 2024. Following treatment, eGFR improved to 84 mL/min/1.73 m2, UPCR decreased to 0.3 g/g and microhematuria resolved. Control biopsy showed reduced proliferative activity, 20% fibrosis, 50% glomerulosclerosis, M1E0S1T0C0 and the C3 deposits disappears Discussion: This case highlights the value of early intervention in IgAN. Histologic diagnosis is essential to guide treatment based on disease pathogenesis. The favorable response to Iptacopan supports inhibition of the complement pathway as a promising strategy in management of IgAN with crescentic and C3 deposits