A novel missense mutation in complement factor I predisposes patients to atypical hemolytic uremic syndrome: a case report

BACKGROUND: Atypical hemolytic uremic syndrome, also called the nondiarrheal form of hemolytic uremic syndrome, is a rare disease characterized by the triad of thrombocytopenia, Coomb’s test-negative microangiopathic hemolytic anemia, and acute renal failure. Approximately 60% of cases of atypical hemolytic uremic syndrome are associated with deficiencies of the complement regulatory protein, including mutations in complement factor H, complement factor I, or the membrane co-factor protein. CASE PRESENTATION: We report the case of a 26-year-old Asian man who presented with pulmonary infection, elevated blood pressure, microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Renal biopsy revealed diffuse capillary fibrin deposition, endothelial swelling, and arteriole narrowing like “onion skinning” consistent with thrombotic microangiopathy. Bidirectional sequencing of CFH, CFHR5, CFHR1, CFI, DGKE, CFB, and MCP confirmed that the patient was heterozygous for a novel missense mutation, p.Cys67Phe, in CFI. This patient had rapid evolution to end-stage renal disease and needed renal replacement therapy. Plasma exchange seemed inefficacious in this patient. CONCLUSIONS: This report confirms the importance of screening patients with atypical hemolytic uremic syndrome for mutations in genes involved in complement system to clarify the diagnosis and demonstrates the challenges in the management of these patients.