Screening of LEP gene polymorphisms as a risk factor for obesity and type 2 diabetes in Iraqis

Document Type : Original article


Department of Biology, College of Science, University of Basrah, Basrah, Iraq


The prevalence of obesity and diabetes changes dramatically with lifestyle and unequal risk among individuals have made scientists interested to understand how the environment interferes with genetic factors to make it so-called genetic predisposition. This study aimed to explore wherethe most variable region is in leptin gene and analyse  microsatellite repeats with direct sequencing in Iraqis and compare our alleles with other populations as a risk for obesity and T2D predisposition. DNA was extracted from blood of 60 type 2 diabetics and 70 non diabetics individuals, LEP 5‛UTR, exon 2 and 3 were screened in 45 individuals (24 type 2 diabetes patients and 21 non- diabetics), LEP TTTC repeats region were amplified in all 130 participants from which 22 control samples were purified and sequenced, superimposed sequences were analyzed manually. Sequencing results showed G>A polymorphism (rs2167270) in 5‛UTR region. No polymorphisms detected in LEP exons 2 and 3. LEP microsatellites alleles were classified depending on sizes into class1 < (220bp) and class2 (> 220bp). Analysis of 22 control samples sequences of microsatellite region resulted in 6 type1 allele (unique sequence) and 5 type 3 allele (13 different isoforms) depending on TTTC arrangement separated by Ts bases. We concluded that LEP variations were in non- coding regions and no significant difference was observed in allele frequency between both groups, but there was a huge diversity in microsatellite repeat number and context among individuals. This may affects gene function thus prepare a predisposition for obesity and type 2 diabetes.


1. Ershow AG. Environmental influences on development of type 2 diabetes and obesity: challenges in personalizing prevention and management. J Diabetes Sci Technol 2009;3:727-734.‏
2. Al-Goblan AS, Al-Alfi MA, Khan MZ. Mechanism linking diabetes mellitus and obesity. Diabetes Metab Syndr Obes 2014;7:587-591.
3. Hu FB. Globalization of diabetes: the role of diet, lifestyle, and genes. Diabetes Care 2011;34:1249-1257.
4. Wu Y, Ding Y, Tanaka Y, Zhang W. Risk factors contributing to type 2 diabetes and recent advances in the treatment and prevention. Int J  Med Sci 2014;11:1185-1200.‏
5. Nguyen NT, Magno CP, Lane KT, Hinojosa MW, Lane JS. Association of hypertension, diabetes, dyslipidemia, and metabolic syndrome with obesity: findings from the National Health and Nutrition Examination Survey, 1999 to 2004. J Am Coll Surg 2008;207:928-934.
6. Dubois L, Kyvik KO, Girard M, Tatone-Tokuda F, Pérusse D, Hjelmborg J, Skytthe A, Rasmussen F, Wright MJ, Lichtenstein P, Martin NG. Genetic and environmental contributions to weight, height, and BMI from birth to 19 years of age: an international study of over 12,000 twin pairs. PLOS One 2012;7:e30153.
7. Morton GJ, Gelling RW, Niswender KD, Morrison CD, Rhodes CJ, Schwartz MW. (2005). Leptin regulates insulin sensitivity via phosphatidylinositol-3-OH kinase signaling in mediobasal hypothalamic neurons. Cell Metab 2005;2:411-420.
8. Yadav VK, Oury F, Tanaka KF, Thomas T, Wang Y, Cremers S, Hen R, Krust A, Chambon P, Karsenty G. Leptin-dependent serotonin control of appetite: temporal specificity, transcriptional regulation, and therapeutic implications. J Exp Med 2011;208:41-52.
9. Qadir MI, Ahmed Z. lep Expression and its role in obesity and type-2 diabetes. Crit RevEukaryot Gene Expr 2017;27:47-51.
10. Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM. Positional cloning of the mouse obese gene and its human homologue. Nature 1994;372:425-432.
11. Moffett S, Martinson J, Shriver MD, Deka R, McGarvey ST, Barrantes R, Ferrell RE. Genetic diversity and evolution of the human leptin locus tetranucleotide repeat. HumGenet 2002;110:412-417.
12. Barrett LW, Fletcher S, Wilton SD. Regulation of eukaryotic gene expression by the untranslated gene regions and other non-coding elements. Cell Mol life Sci 2012;69:3613-3634.
13. Peltonen L, McKusick VA. Genomics and medicine. Dissecting human disease in the postgenomic era. Science 2001;291:1224-1229.‏
14. Wasim M, Awan FR, Najam SS, Khan AR, Khan HN. Role of leptin deficiency, inefficiency, and leptin receptors in obesity. Biochem Genet 2016;54:565-572.‏
15. Fan SH, Say YH. Leptin and leptin receptor gene polymorphisms and their association with plasma leptin levels and obesity in a multi-ethnic Malaysian suburban population. J  physiol Anthropol 2014;33:15.
16. Hinuy HM, Hirata MH, Forti N, Diament J, Sampaio MF, Armaganijan D, Salazar LA, Hirata RD. Leptin G-2548A promoter polymorphism is associated with increased plasma leptin and BMI in Brazilian women. Arq Bras de Endocrinol Metabol 2008;52:611-616.
17. Shigemoto M, Nishi S, Ogawa Y, Isse N, Matsuoka N, Tanaka T, Azuma N, Masuzaki H, Nishimura H, Yoshimasa Y, Hosoda K, Nakao K. Molecular screening of both the promoter and the protein coding regions in the human ob gene in Japanese obese subjects with non-insulin-dependent diabetes mellitus. Eur J Endocrinol 1997;137:511-513..‏
18. Mammes O, Betoulle D, Aubert R, Herbeth B, Siest G, Fumeron F. Association of the G-2548A polymorphism in the 5′ region of the LEP gene with overweight. Ann Hum Genet 2000;64:391-394.
19. Ren W, Zhang SH, Wu JI, Ni YX. Polymorphism of the leptin gene promoter in pedigrees of type 2 diabetes mellitus in Chongqing, China. Chin Med J (Engl) 2004;117:558-561.
20. Iciek R, Wender-Ozegowska E, Seremak-Mrozikiewicz A, Drews K, Brazert J, Pietryga M. Leptin gene, leptin gene receptor polymorphisms and body weight in pregnant women with type 1 diabetes mellitus. Ginekol Pol 2008;79:592-601.
21. Almyah MK, Al-Badran AI. (2019). Genetic susceptibility of Iraqis for obesity and type 2 diabetes: LEPR gene polymorphisms. Gene Rep 15:100386.
22. Shintani M, Ikegami H, Yamato E, Kawaguchi Y, Fujisawa T, Nakagawa Y, Hamada Y, Ueda H, Miki T, Ogihara T. A novel microsatellite polymorphism in the human OB gene: a highly polymorphic marker for linkage analysis. Diabetologia 1996;39:1398-1401.
23. Karvonen MK, Pesonen U, Heinonen P, Laakso M, Rissanen A, Naukkarinen H, Valve R, Uusitupa MI, Koulu M. Identification of new sequence variants in the leptin gene. J Clin Endocrinol Metab 1998;83:3239-3242.‏
24. Dmitriev DA, Rakitov RA. Decoding of superimposed traces produced by direct sequencing of heterozygous indels. PLoS Comput Biol 2008;4:e1000113.
25. Elbaz R, Dawood N, Mostafa H, Zaki S, Wafa A, Settin A. Leptin gene tetranucleotide repeat polymorphism in obese individuals in Egypt. Int J Health Sci (Qassim) 2015;9:63-71.
26. Das B, Pawar N, Saini D, Seshadri M. Genetic association study of selected candidate genes (ApoB, LPL, Leptin) and telomere length in obese and hypertensive individuals. BMC Med Genet 2009;10:99.
27. Deka R, Jin L, Shriver MD, Yu LM, DeCroo S, Hundrieser J, Bunker CH, Ferrell RE, Chakraborty R. Population genetics of dinucleotide (dC-dA) n.(dG-dT) n polymorphisms in world populations. Am J Hum Genet 1995;56:461-474.
28. Belgardt BF, Brüning JC. CNS leptin and insulin action in the control of energy homeostasis. Ann N Y Acad  Sci 2010;1212:97-113.
29. Enns JE, Taylor CG, Zahradka P. Variations in adipokine genes AdipoQ, Lep, and LepR are associated with risk for obesity-related metabolic disease: the modulatory role of gene-nutrient interactions. J Obes 2011;2011:168659.‏
30. Neel JV. Diabetes mellitus: a “thrifty” genotype rendered detrimental by “progress”? Am  J Hum Genet 1962;14:353-362.
31. Payseur BA, Nachman MW. Microsatellite variation and recombination rate in the human genome. Genetics 2000;156:1285-1298.