Research Paper (undergraduate) from the year 2021 in the subject Medicine - Epidemiology, grade: 1.0, Walden University, language: English, abstract: Background: COVID-19 has continued to generate concerns from across the globe with symptoms ranging from mild to acute ones. The disease has been linked to angiotensin-converting enzyme (ACE) 1 and 2, but ACE1 has been lowly researched. Aim: To conduct a systematic review that explores the role of Angiotensin-Converting Enzymes ACE1 and ACE 2 in COVID-19 Infection and the clinical conditions of the patients with the disease. Materials and Methods: the guidelines of PRISMA were used to select 40 journal articles across various databases namely PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), and Embase for researches between 2019 and 2021. Various key terms were employed in the search process, such as "Covid-19," "Covid," "Corona Virus," "ACE," "Angiotensin-Converting Enzyme," “SARS-CoV-2,” “ACE1,” “ACE2,” and “angiotensin receptors.” The search terms were combined using Boolean operators “and/or” incomplete sentences affiliated with the topic in order to generate substantial results. Results: COVID-19 pathologies/severity are affiliated with inverse proportionality of ACE1/ACE2 ratio. High ACE2 levels in adults act as the targets for COVID-19 while in children the high level of ACE2 is not associated with the disease’s severity. ACE1 contributes to cytokine production, which contributes to ARDS. Discussion: Imbalanced ratio of ACE1/ACE2 increase COVID-19 severity. However, the findings apply to patients with hypertension, and therefore, more research would be needed for other pathologies of COVID-19. Conclusion: Both the ACE1 and ACE2 are affiliated with COVID-19 severity. Therefore, ACE1/ACE2 activities can be used as markers to reflect the clinical conditions of COVID-19, thereby helping to manage the disease efficiently.