Amal Ahmed MohamedAbdullah Taher AlanaziHoda H. AhmedSamar ElfikyMuhammad T Abdel GhafarIngy MaherSherin A. TahaMohammed Zakaria Ali Abu RahmaWaleed ElagawyDina A. MoharebAbeer M. RawyHeba M. AbostateAmira AlSayed YoussefDalia Saeed ElsayedRasha M. Abdel-Hamid2025-05-202025-05-202025-05-13Mohamed, A. A., Alanazi, A. T., Ahmed, H. H., Elfiky, S., Ghafar, M. T. A., Maher, I., Taha, S. A., AbuRahma, M. Z. A., Elagawy, W., Mohareb, D. A., Rawy, A. M., Abostate, H. M., Youssef, A. A., Elsayed, D. S., & Abdel-Hamid, R. M. (2025). FokI polymorphism of the vitamin D receptor gene: Linking COVID-19 risk to genetic susceptibility in children. Cytokine, 191, 156958. https://doi.org/10.1016/j.cyto.2025.156958https://doi.org/10.1016/j.cyto.2025.156958https://repository.msa.edu.eg/handle/123456789/6420SJR 2024 1.108 Q1 H-Index 142Background Vitamin D receptor (VDR), influenced by gene polymorphisms like FokI, may affect susceptibility to infections, including coronavirus disease 2019 (COVID-19). Since studies in children are limited, we aimed to analyze the correlation between the VDR FokI variant and both the incidence and severity of COVID-19 in Egyptian children. Methods Seventy-seven COVID-19-positive and 107 COVID-19-negative pediatric patients were included. Participants' serum 25(OH)D levels, inflammatory biomarkers, and demographics were evaluated. Real-time polymerase chain reaction (PCR) was used for genotyping the VDR FokI (rs2228570) polymorphism. Results Absolute lymphocyte count (ALC) was significantly lower in COVID-19 patients than in controls, while interleukin-6 (IL-6), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), procalcitonin, and D-dimer were significantly higher (all p < 0.001). Vitamin D insufficiency was significantly more common in COVID-19 cases (18.2 % versus 3.7 %, p = 0.002). Male sex, increased tumor necrosis factor-alpha (TNF-α), and CRP were significantly associated with severe COVID-19 (p = 0.032, 0.029, < 0.001, respectively). The FokI TT genotype in codominant and recessive models and the T allele in the multiplicative model were significantly correlated with 2.4, 3.0, and 1.8 folds increased COVID-19 risk (p = 0.043, < 0.001, and 0.004, respectively). However, VDR FokI variants did not significantly associate with severe COVID-19. Conclusion The T allele and TT genotype of the FokI variant in the VDR gene increase susceptibility to COVID-19 but not its severity in Egyptian children. Additional research is required to validate the potential role of vitamin D and its receptor polymorphism in COVID-19.en-USCOVID-19 , Pediatric , Inflammatory biomarkers , Vitamin D receptor , FokI polymorphismArticlehttps://doi.org/10.1016/j.cyto.2025.156958