Overactivation of Complement Alternative Pathway in Postpartum Atypical Hemolytic Uremic Syndrome Patients with Renal Involvement

Problem Postpartum atypical hemolytic uremic syndrome (aHUS) is a life‐threatening syndrome with unclear pathogenesis. The current study aimed to investigate the clinical and pathological features, complement activation status, and the genetic variations in a Chinese cohort of patients with renal biopsy‐proven postpartum aHUS. Method of study Five patients with postpartum aHUS were recruited. Renal biopsy specimens were examined and scored. Plasma levels of complements were detected, and coding sequences of complement regulators were screened. Anti‐CFH/CFI autoantibodies were further detected. Results Patients with postpartum aHUS patients presented with severe clinical manifestations and renal involvement. The renal biopsies of the five patients showed typical features of thrombotic microangiopathies. The levels of the following complement components, C4d, Bb, C3a, C5a, and SC5b‐9, were significantly elevated in patients with postpartum aHUS compared with normal non‐pregnant controls. The plasma levels of CFH and CFI significantly decreased in patients with postpartum aHUS compared with normal pregnant women. Three CFH single nucleotide polymorphisms (SNPs) were identified in the five patients. Two patients presented with CFH autoantibodies. Conclusion Postpartum aHUS is a clinical syndrome with severe renal damage. Genetic deficiencies and autoantibodies of CFH may lead to alternative pathway overactivation and participated in the pathogenesis of postpartum aHUS.