IntroductionDiabetes mellitus (DM) is a rapidly expanding healthcare burden due to its significant influence on morbidity, mortality, and healthcare expenditures1. According to the International Diabetes Federation (IDF), 537 million people worldwide were estimated to have diabetes in 2021. By 2045, it is anticipated that this number will reach 783 million2. Globally, the prevalence of DM is increasing rapidly, and 80% of DM patients live in low- and middle-income nations (LMICs)3. Type 2 diabetes mellitus (T2DM), which accounts for approximately 90% of all cases of DM, is a diverse collection of illnesses that arise from decreased insulin production and/or resistance, both of which lead to hyperglycemia2. A significant portion of people with type 2 diabetes are obese, and a rise in body fat percentage continues to be a key risk factor for insulin resistance4. Apart from the impact of nutrition and lifestyle, there has been a recent focus on the importance of genetic background in T2DM risk assessment, and several loci were shown to be linked to T2DM risk in many patient cohorts5.Vitamin D, traditionally recognized for its crucial role in calcium and phosphate homeostasis and bone health, has gained considerable attention in recent years for its pleiotropic effects extending beyond skeletal metabolism6. Emerging evidence from epidemiological and clinical studies increasingly links vitamin D deficiency to an elevated risk of various chronic diseases, including cardiovascular diseases, certain cancers, autoimmune disorders, and notably, T2DM7. Vitamin D is thought to play a role in regulating insulin secretion by directly affecting pancreatic beta-cell function and proliferation. Furthermore, it may enhance insulin sensitivity in peripheral tissues and reduce systemic inflammation, both of which are critical factors in the development and progression of insulin resistance and T2DM8. Vitamin D exerts its effects by attaching to the vitamin D receptor (VDR), a nuclear receptor family ligand-induced transcription factor implicated in several pathological processes9. The vitamin D receptor gene is located on the long arm of chromosome 12 (12q13.1) and is composed of 11 exons10. The 5′ coding region of the VDR gene contains the polymorphic site of the restriction enzyme FokI, and the genotypes of the FokI polymorphisms were found to be FF, Ff, and ff11. The polymorphic form (f) of the polymorphism results in the translation of a longer variant of the VDR protein (427 amino acids), which may function less well than the shorter variant (424 amino acids) translated by the F allele12.Although VDR FokI gene polymorphisms have been widely studied in the context of vitamin D deficiency and T2DM risk, the conclusions of the study on the role of these polymorphisms are inconsistent and provide contradictory data13. Some studies have found strong associations between gene polymorphisms and these disorders, while others have not14. Given the unique genetic makeup of Ethiopian communities, including different ethnic groups, studying the link between the VDR FokI gene polymorphism and T2DM in this context is essential. While earlier research has investigated the relationship between VDR FokI polymorphisms and T2DM, results have been inconsistent. These discrepancies may be due to numerous factors, including differences in study design, sample size, demographic characteristics, and environmental factors15. In spite of the rising prevalence of T2DM in Ethiopia, inadequate studies have explored the role of VDR FokI polymorphisms in this population16. Given the unique genetic makeup of Ethiopian communities, including different ethnic groups, studying the link between the VDR FokI gene polymorphism and T2DM in this context is essential. This study aimed to investigate the association between FokI gene polymorphisms and type 2 diabetes risk in the Ethiopian population.Materials and methodsEthics approval and consent to participateThe institutional review board at the University of Gondar gave the study protocol approval (IOB/327/07/2023) on July 18, 2023. Study participants were enrolled only after informed written consent was obtained from each participant. All the information was collected in an anonymous manner and handled carefully. The guiding principles of the Helsinki Declaration were followed throughout the entire data-gathering process.Study participantsA hospital-based matched case-control study was carried out at the University of Gondar Comprehensive Specialized Hospital from August to December 2023. Treatment and patient follow-up at the chronic follow-up clinic (CFC) are recommended for severe chronic illnesses, including T2DM. The source population consisted of all CFC patients, and the study participants were T2DM patients who were being monitored. Any nondiabetic, healthy volunteers who were available and matched for age and sex during the research period served as the study’s controls.Inclusion and exclusion criteriaPatients with type 2 diabetes whose blood glucose test results were confirmed were recruited for this study. The study comprised patients who had been getting follow-up care at the CFC for a minimum of one year, in line with our earlier research17,18. Age- and sex-matched healthy persons without diabetes who had normal blood glucose test results and had the same socioeconomic position and geographic region served as the controls. Individuals with long-term noncommunicable illnesses or persistent infections with viruses or bacteria were not included. Additionally, this study did not include patients who were unwilling or unable to give informed consent.Sample size determination and sampling techniqueThrough the use of an independent t test, the sample size was determined using G* Power version 3.1.9.419. The following parameters were used: alpha = 0.05, power (1−β) = 0.8 (80%), effect size (d) = 0.5, allocation ratio N2/N1 = 1, and as similar studies were not conducted in the Ethiopian population. A total of 140 people of both sexes participated in the study; 70 of them were T2DM patients, and the remaining 70 were healthy, non-diabetic controls. From among all registered patients, participants were chosen using basic random sampling techniques using a table of random numbers (TRN) as outlined in our previous research works17,18.Data collection and laboratory methodsThe socio-demographic and behavioral characteristics of both patients and healthy control subjects were taken through a semi-structured interviewer questionnaire. The questionnaire was adapted from the “WHO step-wise approach to chronic disease risk factor surveillance (STEPS)”20. The questionnaire was initially prepared in English, translated into the local language (Amharic) in order to obtain the required information from the respondents, and translated back to English to check for any inconsistencies in the meaning of words by language experts21. A pretest was done among 5% of the sample population among individuals in other hospitals that were not included in the main study. Biochemical tests for glucose and other relevant markers were performed using standardized laboratory methods with established reliability and validity20. Quality control measures were implemented to ensure the accuracy of the laboratory results. The data were collected by professional health workers, such as nurses and laboratory technologists, under the supervision of the principal investigator. The laboratory personnel collected a five milliliter blood sample from the median cubital vein of each participant, including patients and healthy controls, in accordance with safety protocols. Out of the 5 ml sample, 3 ml was maintained in the test tube to allow the blood to coagulate. After the serum was extracted via centrifugation, the tubes were replaced with fresh tubes for biochemical analysis. Using the Dimension EXL 200 completely automated analyzer, enzymatic analyses of glucose were carried out on each test in the diagnostic laboratory of the University of Gondar Comprehensive Specialized Hospital. Participants were categorized as diabetic if their fasting blood sugar (FBG) was ≥ 126 mg/dl, if their fasting blood sugar (RBG) was ≥ 200 mg/dl, or if they were treated with insulin or oral hypoglycemic agents; prediabetic if their FBG was 100–125 mg/dl or if their RBG was 140–199 mg/dl; and normal if their FBG was 0.05) in the control groups (X^2 = 3.61), with the f and F allele frequencies recorded at 0.52 0.48, respectively. This suggests that the genotype distribution in the control group supports the reliability of the genotypic data. In the patient group, the frequencies of the ff, Ff, and FF genotypes were 57.1%, 27.1%, and 15.1%, respectively, whereas in the control group, the corresponding values were 32.8%, 38.5%, and 28.5%, respectively. However, compared to those in healthy controls, FokI genotypes Ff and FF were less frequent in T2DM patients (Fig. 4).Table 2 Distribution of FokI genotypes and allele frequencies of the study participants at the university of Gondar comprehensive specialized hospital, Northwest ethiopia, 2023.Full size tableFig. 4Distribution of the FokI genotype in T2DM patients and nondiabetic control.Full size imageAssociations between FokI genotypes and sociodemographic characteristicsThe sociodemographic and behavioral variables of both patients and controls in relation to the FokI genotype distributions are given in Table 3. The FokI genotypes (ff, Ff and FF) in the study groups were assessed for age, sex, residential area, marital status, educational status, family history, religion, occupation, alcohol intake, physical exercise, diet, and smoking habits. None of the variables were significantly related to the genotypes in the study groups (p > 0.05).Table 3 Association of the FokI genotypes with sociodemographic and behavioral characteristics at the university of Gondar comprehensive specialized hospital, Northwest ethiopia, 2023.Full size tableDiscussionThe FokI gene polymorphism is potentially associated with T2DM and could support the progression of diabetes complications24. However, there are conflicting reports regarding FokI gene polymorphisms and T2DM risk13. In the present study, FokI gene polymorphisms were examined in T2DM patients and nondiabetic controls. The frequencies of the ff genotype and f allele were significantly greater in the T2DM patients (57.1% and 70.7%, respectively; P T) does not associate with type 2 diabetes mellitus. Endocr. Res. 00 (00), 1–5. https://doi.org/10.1080/07435800.2017.1305965 (2017).Article CAS Google Scholar Li, L., Wu, B., Liu, J. & Yang, L. Vitamin D receptor gene polymorphisms and type 2 diabetes. 44, 235–241. https://doi.org/10.1016/j.arcmed.2013.02.002 (2013).de Moura, S. S. et al. Vitamin D deficiency and VDR gene polymorphism FokI (rs2228570) are associated with diabetes mellitus in adults: COVID-inconfidentes study. Diabetol. Metab. Syndr. 16 (1), 1–13. https://doi.org/10.1186/s13098-024-01328-6 (2024).Article CAS Google Scholar Ata, A., Emam, W., Ibrahim, G. & Saadawy, S. Vitamin D receptor FokI (rs2228570) polymorphism in diabetic patients. Zagazig Univ. Med. J. https://doi.org/10.21608/zumj.2023.228217.2846 (2023).Article CAS Google Scholar Mahjoubi, I. et al. Lack of association between FokI polymorphism in vitamin D receptor gene (VDR) & type 2 diabetes mellitus in the Tunisian population, Indian J. Med. Res. 144(JULY), 46–51. https://doi.org/10.4103/0971-5916.193282 (2016).Zakaria, W. N. A. et al. Association between vitamin d receptor polymorphisms (Bsmi and foki) and glycemic control among patients with type 2 diabetes. Int. J. Environ. Res. Public. Health. 18 (4), 1–18. https://doi.org/10.3390/ijerph18041595 (2021).Article CAS Google Scholar Sattar, N. A., Shaheen, S., Hussain, F. & Jamil, A. Association analysis of vitamin D receptor gene polymorphisms in North England population with type 2 diabetes mellitus. 21, 1 (2021).Maia, J. et al. The association between vitamin D receptor gene polymorphisms (TaqI and FokI), Type 2 diabetes, and micro-/macrovascular complications in postmenopausal women. https://doi.org/10.2147/TACG.S101410 (2016)Jia, J. et al. Vitamin D receptor genetic polymorphism is significantly associated with risk of type 2 diabetes mellitus in Chinese Han population. Arch. Med. Res. 1–8. https://doi.org/10.1016/j.arcmed.2015.09.006 (2015).Özdemir, A. Ş. Anxiety levels, quality of life and related socio-demographic factors in patients with type 2 diabetes, 775–782. https://doi.org/10.4103/njcp.njcp (2020).Shuhaida, M. H. N. et al. Depression, anxiety, stress and socio-demographic factors for poor glycaemic control in patients with type II diabetes. J. Taibah Univ. Med. Sci. 14 (3), 268–276. https://doi.org/10.1016/j.jtumed.2019.03.002 (2019).Article Google Scholar Hatmal, M. M. et al. Artificial neural networks model for predicting type 2 diabetes mellitus based on vdr gene foki polymorphism, lipid profile and demographic data, Biology (Basel). 9(8), 1–17. https://doi.org/10.3390/biology9080222 (2020).Freitas, R. et al. Association of vitamin D with the TaqI polymorphism of the VDR gene in older women attending the basic health unit of the federal district, DF (Brazil). J. Aging Res. https://doi.org/10.1155/2020/7145193 (2020).Bagci, G., Huzmeli, C., Bagci, B. & Candan, F. Vitamin D receptor polymorphisms in overweight/obese chronic kidney disease patients on dialysis. Turk. J. Nephrol. https://doi.org/10.5152/turkjnephrol.2023.23369 (2023).Article Google Scholar Qadir, J. et al. Vitamin D receptor gene variations and their haplotypic association: possible impact on gastric cancer risk. J. Cancer Res. Ther. 14 (7), 1525–1534. https://doi.org/10.4103/jcrt.JCRT (2023).Article Google Scholar O’Neill, V., Asani, F. F., Jeffery, T. J., Saccone, D. S. & Bornman, L. Vitamin D receptor gene expression and function in a South African population: ethnicity, vitamin D and FokI. PLoS One. 8 (6). https://doi.org/10.1371/journal.pone.0067663 (2013).Yu, D., Shang, Y., Luo, S. & Hao, L. The TaqI gene polymorphisms of VDR and the circulating 1,25-dihydroxyvitamin D levels confer the risk for the keloid scarring in Chinese cohorts. Cell. Physiol. Biochem. 32 (1), 39–45. https://doi.org/10.1159/000350121 (2013).Article CAS Google Scholar Núñez-García, B. A. et al. FokI polymorphism of the vitamin D receptor is closely related to a reduced insulin sensitivity in healthy adults. Clin. Nutr. Open. Sci. 45 (330), 103–111. https://doi.org/10.1016/j.nutos.2022.09.001 (2022).Article Google Scholar Download referencesAcknowledgementsWe would like to express our sincere gratitude to the University of Gondar Comprehensive Specialized Hospital diagnostic laboratory and the University of Gondar molecular biology laboratory staff for providing us with the assistance we required to conduct this study.FundingThe author(s) reported that there is no funding associated with the work featured in this article.Author informationAuthors and AffiliationsDepartment of Biomedical Science, College of Health Science, Debre Tabor University, P. O. Box: 272, Debre Tabor, EthiopiaAddisu MelakeDepartment of Medical Biotechnology, Institute of Biotechnology, University of Gondar, Gondar, EthiopiaEndalech NakachewAuthorsAddisu MelakeView author publicationsSearch author on:PubMed Google ScholarEndalech NakachewView author publicationsSearch author on:PubMed Google ScholarContributionsA.M. and E.N. wrote the main manuscript text and A.M. prepared figures and tables. 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