Coronavirus disease 2019 (COVI-19) was first reported in December, 2019 and virus caused COVID-19 have rapidly spread all over world. Transmission occurs very easily via droplet, aerosol and contact, so mask, hygiene and social distance are important protective factors. Some subjects showed severe findings when some subjects develop disease without any symptoms, so responses to disease differ individually. Genetic structure of subjects may be responsible for different responses. Angiotensin converting enzyme 2 is a polymorphic enzyme and has a crucial role for viral entry. Virus called Severe Acute Respiratory Disease (SARS) Cov-2 uses ACE2 receptor as a substrate to enter into host cells so it is considered that ACE2 gene polymorphism may be responsible for different response to disease. In this study, the distribution of ACE2 gene polymorphism and infected cases were presented in 6 populations all over the world and the related evaluations were made. It has been observed that ACE2 gene polymorphism is protective against the development of COVID-19 disease in Africa and Eastern Mediterranean populations. However, there was no any association between ACE2 gene polymorphism and the number of infected cases in American and European populations. Cytokines are important immune system parameters since they cause cytokine storm. Not only ACE2 gene polymorphisms but also cytokine gene polymorphisms should be investigated for subjects' different responses to COVID-19 disease. Studies should be made to find out responsible factor for these different responses to disease, the associations between gene polymorphisms of other proteins on immune system and development of COVID-19 disease.