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Atypical hemolytic uremic syndrome is a thrombotic microangiopathy caused by the abnormal activation of the alternative complement pathway. Mutations in complement-related genes and autoantibodies against complement regulators are involved in the pathogenesis of this condition; the frequency of, and prognosis of patients harbouring, each genetic mutation varies based on the region and race. Complement factor I (CFI) mutations have been observed in 4%-8% of cases in Europe; however, they have not yet been reported in Japan. We present the first Japanese case of atypical hemolytic uremic syndrome in a patient harbouring a CFI mutation. An 83-year-old female patient presented with severe acute kidney injury, thrombocytopenia, and hemolytic anaemia following a femoral neck fracture. Plasma exchange and haemodialysis were initiated, resulting in improved kidney function and platelet count. However, the platelet count decreased when plasma exchange was discontinued. Therefore, we administered ravulizumab, an anti-complement 5 monoclonal antibody, which led to the maintenance of stable kidney function and platelet count. Genetic analysis revealed a CFI mutation, and the patient was treated with ravulizumab for 2 years without relapse. Individuals diagnosed with atypical hemolytic uremic syndrome harbouring CFI mutations experience poor outcomes, including low rates of remission, high rates of mortality, and progression to end-stage kidney disease. Our case serves as a crucial example demonstrating how prompt identification and appropriate management can lead to better patient outcomes., (© 2025 The Author(s). Nephrology published by John Wiley & Sons Australia, Ltd on behalf of Asian Pacific Society of Nephrology.)

Background: Atopic dermatitis (AD), a prevalent chronic inflammatory skin disorder, is characterized by compromised skin barrier and heightened immune responses. The study investigates the therapeutic efficacy of catestatin (CST), a chromogranin A-derived antimicrobial peptide, in mitigating AD-like symptoms., Methods: Utilizing both keratinocyte cultures and a C57BL/6 mouse model, we examined CST's impact on skin barrier proteins, tight junction (TJ) integrity, inflammatory cytokines, and AD-like symptoms., Results: CST administration led to a significant upregulation of skin barrier proteins and improved TJ function, counteracting the negative effects of Th2 cytokines on these parameters. In a 2,4-dinitrochlorobenzene-induced AD mouse model, CST treatment markedly reduced AD-like symptoms, including ear thickness, transepidermal water loss, and scratching behavior, and normalized barrier protein expression and TJ barrier function. Furthermore, CST was found to interact with the Notch1 receptor, activating the Notch1/PKC pathway, which may underlie its skin barrier-enhancing properties., Conclusions: Collectively, these findings suggest CST as a promising therapeutic agent for AD, capable of enhancing skin barrier function, modulating immune responses, and targeting the Notch1/PKC pathway, offering a novel approach to AD treatment focusing on barrier restoration and immune modulation., Competing Interests: Conflict of interest The authors have no conflict of interest to declare., (Copyright © 2025 Japanese Society of Allergology. Published by Elsevier B.V. All rights reserved.)