Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 11 3 2024 12 28 155 159 Behrooz Farzanegan Critical Care Quality Improvement Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Naghmeh Bahrami Craniomaxillofacial Research Center, Tehran University of Medical Sciences, Tehran, Iran; Department of Tissue Engineering and Applied Cell Sciences, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Fathi Anesthesiology Research Center, Department of Anesthesia and Critical Care, Shahid Modares Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Saba Tahmasebi Anesthesiology Research Center, Department of Anesthesia and Critical Care, Shahid Modares Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Mehdi Kazem Pour Dizaji Department of Biostatistics, Mycobacteriology Research Center, National Research Institute of Tuberculosis and Lung Diseases, Masih Daneshvari Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Shadi Shafaghi Lung Transplantation Research Center, National Research Institute of Tuberculosis and Lung Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Farnaz Ahmadi Lung Transplantation Research Center, National Research Institute of Tuberculosis and Lung Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Farnoush Mohammadi Craniomaxillofacial Research Center, Tehran University of Medical Sciences, Tehran, Iran; Department of Oral and Maxillofacial Surgery, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Seyedeh Zahra Fotook Kiaei Craniomaxillofacial Research Center, Tehran University of Medical Sciences, Tehran, Iran; Department of Pulmonary and Critical Care, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Mona Mohajeri Tehrani Craniomaxillofacial Research Center, Tehran University of Medical Sciences, Tehran, Iran. Masoume Farhangiyan Craniomaxillofacial Research Center, Tehran University of Medical Sciences, Tehran, Iran. Abdolreza Mohamadnia Chronic Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran, And Department of Biotechnology, School of Advanced Technologies in Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 2024 07 09 2024 07 24 Introduction: The Covid 19 illness is triggered by a coronavirus known as SARS CoV-2. This particular virus spreads rapidly likely because of the Spike proteins affinity, to the human ACE2 cell receptor causing harm to organs, like the lungs in type 2 pneumocytes that abundantly express this receptor. Materials and Methods: The research methodology used in this study involved a case control approach. Patients were referred by a specialist following diagnosis. A total of 50 samples, from infectious cases and 50 samples from cases, with mild symptoms were analyzed for statistical purposes. The ACE2 gene expression was assessed using the Realtime RCR method after RNA extraction. Results: The findings indicate that the average age does not have an impact on individuals experiencing mild symptoms. Moreover, there is a decrease in the expression of ACE2 genes in the blood of patients with severe symptoms hospitalized in intensive care units as compared to those, with mild symptoms, highlighting a substantial disparity. Conclusion: The numerical value of fold change for ACE2 gene in severe type patients shows a decrease compared to mild patients and it is 2.11 times lower in severe type patients than mild type. Keywords: COVID-19; ACE2; Realtime RCR. https://jcr.tums.ac.ir/index.php/jcr/article/view/508 https://jcr.tums.ac.ir/index.php/jcr/article/download/508/420