Anti-complement factor I antibody associated atypical hemolytic uremic syndrome - A new insight for future perspective!

Atypical hemolytic uremic syndrome (aHUS) is caused mainly by complement dysregulation. Although various defects in the complement system explaining pathophysiology have been described in recent years, the etiology still remains unclear in about thirty percent of cases. In exploring other causes, similar to anti- complement factor H (anti-CFH) antibody associated HUS, we hypothesized that anti-complement factor I (anti-CFI) antibody could play a role in aHUS. Further, we tried to describe the clinical profile and outcome of those with high anti CFI antibody titers. Eleven of thirty five children (31 %) diagnosed with aHUS from July 2017 to December 2018 had high IgG anti-CFI antibody titers. Median age was 10 months (6, 33) with no sex difference. Thirty-six percent (4/11) had nephrotic-range proteinuria. C3 was low in 8 children (72.7 %) with mean C3 (68.1 ± 14.7 mg/dL). Plasmapheresis was done in 2 children who promptly responded, suggesting the possible role of anti-CFI antibody in pathogenesis of aHUS in these patients. Further studies examining role of anti-CFI antibodies in aHUS is warranted with longitudinal and genetic studies.