Evaluation of complement regulatory components in patients with atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS), a rare disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure, is associated with mutations and polymorphisms in various components and regulators of the complement alternative pathway (AP), including factor H, factor I, membrane cofactor protein (MCP or CD46) and factor B. This impaired regulation of the alternative pathway leads to a procoagulant state with microthrombi formation in the renal vasculature, which influences disease onset and progression.

To evaluate the role of complement regulatory factors in occurrence of aHUS; we also included evaluation of ADAMTS13 activity and autoantibody against ADAMTS13 in order to exclude thrombotic thrombocytopenic purpura (TTP) cases, which might have overlapping clinical and laboratory findings.

This study was conducted on 273 individuals with aHUS. Diagnosis was based on clinical manifestations, kidney function tests, red blood cell count, morphology and reticulocyte count. Then, the ADAMTS 13 autoantibody and activity and also complement factor B, complement factor H (CFH) and complement factor-I (CIF) were analyzed. Finally, the statistical analysis was performed by SPSS software.

The mean age of our patients was 27.3 years, 55% were female and 45% were male. The mean levels of urea and creatinine concentration were 92.9 mg/dl and 5.1 mg/dl, respectively. The mean levels of RBC count, Hb and HCT in these patients were lower than normal but the mean percentage of reticulocyte count was higher than normal (2.5%). The assessment of complement regulatory factors revealed that the B and H factors levels were normal except in two cases but the level of factor I was higher than normal.

According to the results of this study, it seems that up regulation of factor I had a significant role in occurrence of aHUS in our study group.