Research Article Anti-Factor H Antibodies in Egyptian Children with Hemolytic Uremic Syndrome Shereen Shawky, 1 Hesham Safouh, 2 Mona Gamal, 3 Mohammed M. Abbas, 3 Azza Aboul-Enein, 1 Toshihiro Sawai, 4 Yosra Fahmy, 2 and Heba Selim 1 1 Department of Clinical and Chemical Pathology, Faculty of Medicine, Cairo University, Cairo, Egypt 2 Department of Pediatrics, Faculty of Medicine, Cairo University, Cairo, Egypt 3 Department of Clinical and Chemical Pathology, Faculty of Medicine, Fayoum University, Fayoum, Egypt 4 Department of Pediatrics, Shiga University of Medical Science, Seta-Tsukinowa, Otsu, Japan Correspondence should be addressed to Heba Selim; hebaallah.monir@kasralainy.edu.eg Received 18 September 2021; Revised 23 October 2021; Accepted 26 October 2021; Published 18 November 2021 Academic Editor: Franca Anglani Copyright © 2021 Shereen Shawky et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Atypical hemolytic uremic syndrome (aHUS) is an important cause of acute kidney injury in children. It is primarily caused by dysregulation of the complement alternative pathway due to genetic mutations, mainly in complement factor H genes, or due to anti-factor H autoantibodies (anti-FH), leading to uncontrolled overactivation of the complement system. Early diagnosis and treatment of autoimmune HUS (AI-HUS) is essential and leads to a favorable outcome. Methods. Fifty pediatric HUS patients and 50 age- and sex-matched controls were included in the study. Patients were subjected to full history taking, clinical examination, and laboratory testing. All candidates were subjected to an assessment of anti-FH in serum by a homemade enzyme-linked immunosorbent assay technique. Results. A high frequency of serum anti-FH was detected in our aHUS patients. e disease onset of AI-HUS was mainly observed in March and April, with significantly higher rates in school-aged males. All patients who started immunosuppressives early together with plasmapheresis upon detection of their anti-FH had complete renal function recovery. Conclusion. e high frequency of AI-HUS revealed in Egyptian HUS children in our study highlights the importance of implementing anti-FH testing in Egypt to provide early recognition for immediate proper management, including early immunosuppressive therapy, and hence improving patient outcomes. 1. Introduction rombotic microangiopathy (TMA) defines a group of diseases characterized by microangiopathic hemolytic anemia (MAHA), thrombocytopenia, and organ injury [1]. TMAs resulting in acute kidney injury are referred to as hemolytic uremic syndrome (HUS). Most HUS cases are caused by infection with Shiga toxin-producing Escherichia coli (STEC), while nearly 10%, referred to as atypical HUS (aHUS), are associated with uncontrolled activation of the alternative complement pathway (ACP) [2]. aHUS may be due to genetic mutations affecting the genes encoding complement regulatory proteins, more frequently, complement factor H (CFH). In addition, acquired functional CFH deficiency due to anti-factor H autoantibodies (anti-FH) has been observed and termed autoimmune HUS (AI-HUS) [3]. Anti-FH inhibits the regulatory function of CFH at cell surfaces by binding mainly to epitopes within the C-terminus, thus pre- venting it from interacting with C3b, C3d, and heparin and thereby diminishing the protection of host cells against complement attack. Anti-FH might also bind to the CFH N-terminus and middle part, thereby markedly weakening its interactions and interfering with factor I cofactor activity, possibly leading to the neutralization of all CFH functions and causing more severe disease forms [4]. Hindawi International Journal of Nephrology Volume 2021, Article ID 6904858, 8 pages https://doi.org/10.1155/2021/6904858