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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 4  |  Issue : 3  |  Page : 80-85

Contribution of single-nucleotide polymorphism in transcription factor 7-like 2 gene to cardiometabolic risk in adult Nigerians


1 Department of Clinical Pathology, College of Medicine, University of Lagos, Lagos, Nigeria
2 Department of Cell Biology and Genetics, Faculty of Science, University of Lagos, Lagos, Nigeria
3 Department of Molecular Biology, DNA Laboratory, Sickle Cell Foundation Nigeria, Lagos, Nigeria

Date of Web Publication27-Sep-2019

Correspondence Address:
Dr. Ifeoma Christiana Udenze
Department of Clinical Pathology, College of Medicine, University of Lagos, Lagos
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jncd.jncd_1_19

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  Abstract 


Background: Single-nucleotide polymorphism in the gene, transcription factor 7-like 2 (TCF7L2), shows the strongest and most consistent association with risk of developing type 2 diabetes (T2D). TCF7L2 has been associated with both impaired beta-cell function and insulin resistance. Gene variants of TCF7L2 may, therefore, contribute to cardiometabolic risk (CMR) and metabolic syndrome (MS).
Aims and Objectives: The study aims to examine the relationship between gene variants in TCF7L2 with MS and CMR.
Methods: Three hundred and fifty-six adult Nigerians aged between 40 and 100 years participated in a cross-sectional, analytical study. The association between TCF7L2 genotypes and MS and its components was determined. The data were analyzed, and statistical significance was set at P< 0.05.
Results: Three hundred and fifty-six individuals participated in the study (35.6% of males and 64.2% of females). About 64.9% of participants had T2D. The prevalence of MS was 26.4%. Among the individuals with the wild-type homozygote genotype CC, heterozygote genotype CT, and homozygote mutant TT, 24.9%, 27.2%, and 30.6% had MS, respectively. The risk T allele was associated with higher mean values of waist circumference and triglyceride than the C allele (P = 0.006 and 0.022, respectively). The T allele had a significant correlation with MS components (P < 0.05). In multivariate regression analysis, quantitative index of insulin resistance (Quantitative Insulin-Sensitivity Check Index) remained independently associated with the T risk allele (P = 0.033).
Conclusion: Variants in the TCF7L2 gene are associated with components of MS and correlate with CMR through insulin resistance.

Keywords: Cardiometabolic risk, metabolic syndrome, single-nucleotide polymorphism, transcription factor 7-like 2, type 2 diabetes


How to cite this article:
Udenze IC, Taiwo IA, Ojewunmi OO. Contribution of single-nucleotide polymorphism in transcription factor 7-like 2 gene to cardiometabolic risk in adult Nigerians. Int J Non-Commun Dis 2019;4:80-5

How to cite this URL:
Udenze IC, Taiwo IA, Ojewunmi OO. Contribution of single-nucleotide polymorphism in transcription factor 7-like 2 gene to cardiometabolic risk in adult Nigerians. Int J Non-Commun Dis [serial online] 2019 [cited 2019 Nov 14];4:80-5. Available from: http://www.ijncd.org/text.asp?2019/4/3/80/268134




  Introduction Top


The burden of type 2 diabetes (T2D) has been projected to reach alarming proportions in developing countries.[1] In Nigeria, the estimated prevalence rate for T2D is 4.3%, and over 5 million people are projected to be affected by 2030.[2]

In parallel with the T2D pandemic, the prevalence of cardiovascular disease (CVD) complications is increasing globally. Genetic and nongenetic factors have contributed to this trend.[3] Individuals with prediabetes and diabetes are at increased risk of atherosclerotic CVD.[4] The clustering of cardiometabolic risk (CMR) factors of obesity, dysglycemia, dyslipidemia, hypertension, and pro-inflammatory and prothrombotic states in diabetic and nondiabetic individuals is known as the metabolic syndrome (MS).[5]

Several genomic loci have been linked to the pathophysiology of T2D mostly in populations of European ancestry[3] and in African Americans.[6] Single nucleotide polymorphism (SNP) in the gene, transcription factor 7-like 2 (TCF7L2) C/T, reference SNP (rs) cluster identification (rs7903146), shows the strongest and most consistent association with risk of developing T2D of any gene variant identified so far.[3],[6] TCF7L2 (C/T) has been validated to have the strongest and causal association with T2D in African Americans[7] as well as in Africans.[8]

The pathophysiology of this risk variant to T2D has been linked to both impaired beta-cell function and insulin resistance.[9],[10],[11] Insulin resistance is also the initiating step in the development of MS.[12] It is also the first pathology in the spectrum of metabolic aberrations leading to T2D and its cardiovascular complications.[13]

Whether the polymorphism in TCF7L2 gene contributes to CMR has not been documented in adult Nigerians and inclusion of genetic susceptibility to CVD risk classification may result in more accurate CVD risk stratification and management. Therefore, this study investigated the association between SNPs in TCF7L2 gene with CMR in adult Nigerians.


  Methods Top


Three hundred and fifty-six adult Nigerians aged between 40 and 100 years, comprising diabetic and nondiabetic individuals, were enrolled to participate in a cross-sectional, analytical study. The study participants were recruited from endocrinology clinics in tertiary and secondary care public hospitals in Lagos, Nigeria. T2D was defined according to the WHO criteria,[14] and MS was defined according to the harmonized MS criteria.[5] Participants who were functional and cognitively intact were recruited into the study. Those not ambulant, pregnant women, and hospitalized patients were excluded from the study. Eligible study participants were counseled on the objectives of the study and the study protocol. The study was conducted according to the guidelines laid down in the Declaration of Helsinki, and the Institutional Review Board of the College of Medicine, University of Lagos, approved the protocol. Informed consent was obtained from each participant who then completes an interviewer-administered, anonymous, standardized, questionnaire. Participants then underwent anthropometric measurements and blood pressure measurements. Abdominal obesity was determined by measurement of the waist circumference. The measurement was taken at the end of several consecutive natural breaths, at a level parallel to the floor, and midpoint between the top of the iliac crest and the lower margin of the last palpable rib in the midaxillary line.[15] The hip circumference was measured at a level parallel to the floor, at the largest circumference of the buttocks.[15]

General obesity was determined by the body mass index.[16] The weight was measured to the nearest 0.1 kg and height to the nearest 0.1 m.

The blood pressure was determined using the Accoson's mercury sphygmomanometer (cuff size 15 cm × 43 cm). The participants were seated and rested for 5 min before measurement. The systolic blood pressure was taken at the first Korotkoff sound and diastolic at the fifth Korotkoff sound.[17]

The study participants reported on the morning of the study after an overnight (10–12 h) fast. Venous blood was collected for fasting glucose, lipid profile, and insulin measurements. Fasting glucose and lipid profile were estimated from lithium heparin plasma on biochemistry autoanalyzer, Cobas C 311 (Roche Diagnostics GmbH D-68298 Mannheim Germany). Fasting insulin was determined from serum using reagents from Biovendor Laboratories (62100 Brno, Czech Republic) by an enzyme-linked immunoassay technique on Acurex Plate Read (Acurex Diagnostics, Ohio, USA, 419-872-4775). Insulin resistance was assessed using the Quantitative Insulin-Sensitivity Check Index (QUICKI) and calculated as: QUICKI = 1/(log (Insulin μU/mL) + log (Glucose mg/dL).[18]

Genomic DNA was prepared from leukocytes in peripheral whole-blood samples using column extraction method based on the manufacturer's protocols (Qiagen, Germany). The TCF7L2 (rs7903146) SNP was genotyped at the Institute for Cardiogenetics, Germany. The polymorphism was detected by polymerase chain reaction (PCR) followed by allelic discrimination on Applied Biosystems 7900HT Fast Real-Time PCR System using fluorescent-based PCR chemistry based on methods already described.[19]

Taqman® Universal PCR Master Mix and selected probes and primers were ordered from Taqman® assays (Applied Biosystems, Foster City, CA). The allelic discrimination assay is a multiplexed (more than one primer/probe pair per reaction) end-point assay that detects variants of a single nucleic acid sequence. The presence of two primer/probe pairs in each reaction allows genotyping of the two possible variants at the single-nucleic polymorphism (SNP) site in a target template sequence. The actual quantity of target sequence is not determined.[19] For each sample in the allelic discrimination assay, a unique pair of fluorescent dye detectors was used. One fluorescent dye detector, the-2′-chloro-7′phenyl-1,4-dichloro-6-carboxyfluorescein (VIC) dye-labeled probe, is a perfect match to the wild-type and binds allele 1 (CC) and the other fluorescent dye detector, the fluorescein amidite dye-labeled probe, is a perfect match to the mutation and binds allele 2 (TT).[19] The allelic discrimination assay measures the change in fluorescence of the dyes associated with the probes. When the two dye-labeled probes bind, a heterozygote allele is present (CT).[19]

The Applied Biosystems software (Foster City, California, USA) is used to determine the number of wild-type, heterozygote, and mutant alleles present in the sample.[19]

All PCR reactions took place in optical 384-well reaction plates (Applied Biosystems). Each well consists of 5 μU of genomic DNA and 5 μU of the PCR master mix, primer-probe pair, and PCR grade water. The TaqMan genotyping reaction was amplified on a GeneAmp PCR system 7000, and fluorescence was detected on an ABI PRISM 7000 sequence detector (Applied Biosystems).[19] Samples were done in duplicates, and five percent of samples were regenotyped for quality control. The percent agreement between blind duplicates was 98.5%.

Statistical analysis

The data were analyzed using the IBM SPSS statistical package version 23.0 (Chicago, IL, USA). The Chi-square test, Student's t-test, and Pearson's correlation and multivariate analysis were employed for the analysis. Genotypes and allele frequency between groups were compared using Fisher's exact test. Hardy–Weinberg equilibrium analysis was performed to compare the observed and expected frequencies using the Chi-square test. P < 0.05 was considered statistically significant.


  Results Top


Three hundred and fifty-six adult Nigerians participated in this study. About 64.9% had T2D and 26.4% had MS. About 35.5% were male and 64.2% were female. The age range was 40–98 years, with a mean of 56.30 ± 10.78 years.

[Table 1] shows the sociodemographic data of the study participants. The sociodemographic characteristics of the study participants were evaluated by age, gender, ethnicity, educational level, presence of T2D, and religion by the presence or absence of MS. The study participants with and without MS were similar by age, ethnicity, level of education, and religion. They differed significantly by gender and presence of T2D.
Table 1: Sociodemographic data of the study participants with and without metabolic syndrome by age, gender, ethnicity, educational level, presence of type 2 diabetes, and religion

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The study participants differed significantly by gender and presence of T2D. More females had MS (75.5%) compared to males (24.5%). MS occurred more frequently in individuals with T2D (79.1%) compared to individuals without T2D (64.9%). Individuals with MS had lower levels of education, but the difference was not statistically significant. There were no statistically significant differences in the study participants in other sociodemographic parameters such as age, ethnicity, and religion.

[Table 2] shows the distribution of the TCF7L2 genotypes such as wild-type homozygote genotype CC, heterozygote genotype CT, and homozygote mutant TT and their relationship with MS in the study participants.
Table 2: The relationship between the transcription factor 7-like 2 genotypes such as wild-type homozygote genotype CC, heterozygote genotype CT, and homozygote mutant TT, with metabolic syndrome in adult Nigerians

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The relationship between TCF7L2 genotypes and MS using either the dominant, recessive, or allelic model was not statistically significant.

[Table 3] compares the mean values of CMR factors in individuals who are heterozygous or homozygous for the T allele with those homozygous for the C allele.
Table 3: Comparison of mean values for the cardiometabolic risk factors of hypertension, obesity, glucose tolerance, lipid profile, and insulin resistance in individuals heterozygous or homozygous for the T allele (CT + TT) with those homozygous for the C allele (CC)

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Individuals with the T allele (CT + TT) had a statistically significant increase in waist circumference, triglyceride, low-density lipoprotein (LDL)-cholesterol, total cholesterol, and lower values of QUICKI, indicating higher values of insulin resistance, compared to the individuals who are homozygous for the C allele (CC).

[Table 4] shows the CMR factors of waist circumference, triglyceride, total cholesterol, and QUICKI, with significant correlations with the T allele.
Table 4: The cardiometabolic risk factors of waist circumference, triglyceride, total cholesterol, and Quantitative Insulin-Sensitivity Check Index, with significant correlations with the T allele of the single-nucleotide polymorphism of transcription factor 7-like 2 (C to T transition) gene in the study participants

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The CMR factors of waist circumference, triglyceride, total cholesterol, and insulin resistance, as measured by QUICKI, had a significant correlation with the T allele of the single-nucleotide polymorphism of TCF7L2 (C/T) gene in the study participants. After correcting for presence of type 2 diabetes mellitus and gender, insulin resistance, as measured by QUICKI, remained independently associated with TCF7L2 genotypes r = −0.336, P = 0.015. The negative correlation of QUICKI with T allele shows that lower values of QUICKI indicate a higher insulin-resistant state in the presence of the T allele.

[Table 5] shows the regression of the CMR factors of waist circumference, triglyceride, total cholesterol, and QUICKI, on the T allele.
Table 5: Multivariate regression of the cardiometabolic risk factors of waist circumference, triglyceride, total cholesterol, low-density lipoprotein-cholesterol, and Quantitative Insulin-Sensitivity Check Index, on the T allele of the single-nucleotide polymorphism of transcription factor 7-like 2 (C to T transition) gene in the study participants

Click here to view


Multivariate regression of CMR factors of waist circumference, triglyceride, total cholesterol, LDL- cholesterol, and QUICKI on the T allele of the single- nucleotide polymorphism of TCF7L2 (C/T) gene showed insulin resistance, as measured by QUICKI, to be independently associated with the T allele.


  Discussion Top


The T allele, which is the risk allele in the single-nucleotide polymorphism in T2D susceptibility gene, TCF7L2, rs7903146 (C/T), is associated with increased CMR factors in adult Nigerians, through insulin resistance.

TCF7L2 is a high mobility group box-containing transcription factor that serves as a nuclear receptor for β-catenin, which mediates the wingless-type MMTV integration site family (WNT) signaling pathway, a key developmental and growth regulatory mechanism of the cell.[20] Recently, the TCF7L2 gene on chromosome 10q25.2 has been linked with T2D and insulin resistance in many populations,[6],[7],[8],[9],[10],[11] suggesting that WNTs play a pivotal role in regulating pancreatic beta-cell function and mass.

A recent review documents the contributions of dysregulation in WNT signaling to features of the MS,[21] but the contribution of TCF7L2, rs7903146 (C/T), specifically, to CMR has produced different results in different populations.[22],[23],[24]

This study reports a positive relationship between the T allele of the TCF7L2, rs7903146 (C/T), polymorphism with obesity, as measured by waist circumference and hyperlipidemia (triglyceride, LDL-cholesterol, and total cholesterol) in an adult population, with and without MS. This is similar to findings in a lifestyle intervention study exploring gene–environment interactions, where individuals with polymorphisms in the TCF7L2, rs7903146, had higher BMI and more difficulty in losing visceral and nonvisceral fats following a 9-month diet and exercise therapy.[22] The T allele also showed association with increased triglyceride but not total cholesterol and apo-B particles in individuals with familial hypercholesterolemia.[23] An analysis of the association of variants in the TCF7L2, rs7903146, with cardiometabolic traits in the general population showed a decreased waist circumference and decreased triglyceride and total cholesterol in the carriers of the risk T allele, though the study was in an elderly population of adults ≥65 years of age, and age-associated changes may explain the differences seen in that study.[24],[25]In vivo andin vitro studies have shown that the TCF7L2 protein is a key transcriptional effector of the WNT/β-catenin signaling pathway which negatively regulates adipogenesis. Its expression is required for the regulation of WNT signaling during adipogenesis and inactivation of TCF7L2 protein, resulted in a phenotype associated with increased subcutaneous adipose tissue mass, and adipocyte hypertrophy.[26],[27]

After correcting for presence of T2D and gender, single-nucleotide polymorphism in the TCF7L2, rs7903146, was independently correlated with insulin resistance (as measured by QUICKI), and this is in keeping with findings in literature.[20],[21],[22],[23],[24] The presence of the T allele was associated with increasing levels of insulin resistance, abdominal obesity, and dyslipidemia. Increased values of the adipokine resistin, in obesity, create the condition of insulin resistance which promotes a state of dyslipidemia and increased CMR.

This study was limited by its cross-sectional design which made it difficult to determine causality and also by its small sample size which may have limited the findings. Future directions in this area will be the conduction of a systematic review on the association of the TCF7L2, rs7903146 single-nucleotide polymorphism with CMR. Conclusions from a systematic review will aid CVD risk profiling in both in individuals with T2D and in the general population.


  Conclusion Top


Single-nucleotide polymorphism in the TCF7L2 gene, rs7903146 (C/T), is associated with obesity and dyslipidemia, CMR factors, through the mechanism of insulin resistance. Inclusion of genetic susceptibility to cardiovascular (CVD) risk classification algorithm may improve CVD risk stratification and management.

Acknowledgment

The authors acknowledge laboratory support from the Institute of Cardiogenetics, University of Luebeck, Germany.

Financial support and sponsorship

“The research reported in this publication was supported by the Central Research Committee grant (Grant number: 2017/15) of the University of Lagos, Nigeria.”

Conflicts of interest

There are no conflicts of interest.



 
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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