Low plasma levels of the vitamin D metabolite 25-hydroxyvitamin D [25(OH)D] and the vitamin D receptor (VDR) gene single nucleotide polymorphisms (SNPs) have been associated with the body’s susceptibility to infectious diseases, including COVID-19. In this pilot retrospective study, representatives of the Kazakh population (central Kazakhstan) were divided into groups based on the test for IgM and IgG for coronavirus infection. We compared the 25(OH)D plasma levels and concluded that the COVID-19-positive group values (25.17 ng/mL ± 16.65) were statistically lower (p = 0.0114) compared to the COVID-19-negative ones (35.58 ng/mL ± 20.67). There was no association between age, gender and 25(OH)D concentration within the groups (p > 0.05). The genotyping of rs2228570 was performed using a TaqMan Real-Time PCR assay. Allele C predominated among the COVID-19-negative participants and significantly reduced the likelihood of coronavirus infection (p < 0.0001; OR = 0.0804; 95% CI 0.02357–0.2798). There were no statistically significant differences in the frequencies of the A, G and T alleles in the studied groups (p > 0.05). The GG genotype of rs2228570 was associated with a 4.131-fold increased likelihood of COVID-19 infection (p = 0.0288; χ² = 5.364; OR = 4.131; 95% CI 1.223–13.71). Comprehensive studies are required to determine whether low 25(OH)D plasma concentrations and genetic background represent a risk factor for COVID-19 infection.

There is still no definitive confirmation regarding the association between ACE2 gene polymorphisms and COVID-19. This study was conducted to analyze the distribution of alleles and genotypes of the ACE2 gene rs2285666 and rs35803318 two polymorphisms and their possible association with COVID-19 among two ethnic groups, namely, the Kazakhs and Eastern Slavs, residing within the same geographic area in the city of Karaganda, Republic of Kazakhstan. This research was conducted for the first time in Kazakhstan. The genotyping was performed using the Amplification-Refractory Mutation System (ARMS) PCR. A substantial connection of rs2285666 with COVID-19 in the studied Kazakh and Eastern Slavs populations (p>0.05) was not observed. It has been determined that certain alleles and genotypes serve as protective markers against COVID-19. It was determined that the G allele (p = 0.0217) of rs2285666 among Kazakh men reduced the likelihood of coronavirus infection. It was concluded that the C allele and CC genotype of rs35803318 have a statistically significant association with protection against COVID-19 among only Eastern Slavs. There were no differences in the alleles and genotypes of polymorphism between males and females. Thus, the analysis of the rs2285666 and rs35803318 polymorphisms has revealed that these two variants of the ACE2 gene do not exert an influence on the risk of contracting COVID-19.

In the article the results of genotyping of DNA samples obtained from the study participants on the single nucleotidepolymorphism (SNP) rs35803318 (C/T) of the ACE2 gene were presented. Genotyping was carriedout by real-time polymerase chain reaction (PCR) using the technique Amplification of the Refractory MutationSystem (ARMS). The frequencies of rs35803318 (C/T) genotypes and alleles in 96 representatives of theKazakh ethnic group living in the Karaganda region were analyzed. The ACE2 gene (angiotensin-convertingenzyme 2) was extensively investigated due to its role in susceptibility to infection by the SARS-CoV-2 viruscausing COVID-19. The ACE2 gene encodes a protein that serves as a receptor for the virus, and its variationscan affect a person's susceptibility to infection. The ACE2 protein plays a role in the regulation of angiotensinand the effect on blood pressure. Therefore, there is a link between ACE2 gene polymorphisms, includingrs35803318, and the development of cardiovascular diseases. According to the results of our study,the CT genotype (63.5 %) is the most common among Kazakhs, the CC genotype was 20.8 % and theTT genotype was 15.6 %. The distribution of polymorphism alleles is as follows: allele C — 52.6 %, allele A— 47.4 %.