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KCNQ1 rs2237895 polymorphism is associated with Gestational Diabetes in Pakistani Women.

Byline: Syeda Sadia Fatima, Bushra Chaudhry, Taseer Ahmed Khan and Saad Farooq

ABSTRACT

Background and Objective: Genetic studies on gestational diabetes (GDM) are relatively scarce; moreover, limited data is available for KCNQ1 polymorphism in Pakistani pregnant women. We aimed to determine the frequency of KCNQ1 rs2237895 in GDM and normal pregnant controls and its association with GDM-related phenotypes.

Methods: A total of 637 pregnant females (429 controls and 208 cases) in their second trimester were classified according to the International Association of the Diabetes and Pregnancy Study criteria in this study. Their blood samples were genotyped for KCNQ1 SNP rs2237895 using PCR-RFLP method and sequencing. Fasting and two hour-post glucose load blood levels, serum HbA1c, insulin, and anthropometric assessment was performed. Pearson's Chi Square test, Mann-Whitney U test, and regression analyses were performed. A p-value of 0.05). The rs2237895 showed an association with GDM (OR 2.281; 1.388-3.746: p 97%. A genotyping quality control was performed in 50% of the samples by duplicate checking (rate of concordance in duplicates was >99%). Further reconfirmations of genotyping accuracy were made by sequencing 20% of the samples with detected polymorphic variants (discrepancy rate was <0.20%) (ABI3730XL, automated DNA sequencer, Macrogen, Korea) (Fig.1).

Statistical Analysis: Statistical analyses were conducted using the IBM Statistical Package for the Social Sciences (IBM SPSS version 21; IBM Corp Inc, Armonk, NY). Descriptive analysis of categorical data was presented in terms of frequencies and percentages whereas that for continuous variables was expressed as mean +- standard deviation. Mann Whitney U test and Pearson chi-square test of independence were used for comparing continuous and categorical variables wherever applicable. Hardy-Weinberg equilibrium (HWE) was calculated for SNP data. SNP data was analysed for genotype and allele frequency determination by applying chi-squared statistics. Significance of risk allele with study parameters was determined with regression analyses. Genotypes were allotted code of 0/1/2 rendering the number of minor alleles under an additive model of inheritance.

RESULTS

Six hundred and thirty-seven pregnant females were recruited in this study. The GDM group had a higher BMI, pre and post load GTT, HBA1c and insulin levels (p<0.01) when compared to pregnant controls (Table-I).

Table-I: Clinical and biochemical data of cases and controls.

Variables###Control n=429###Case n=208

###Mean +- S.D###Mean +- S.D

Age (in year)###25.97 +- 4.87###27.31+- 5.56

Weight at Booking (kg)###57.55 +- 10.15###63.84+- 12.58**

BMI at Booking (kg/m2)###22.77 +- 4.19###24.83 +- 5.13**

GTT 0 hr (mg/dl)###78.69 +- 8.96###106.23 +- 20.70 **

GTT 2 hr (mg/dl)###124.22 +- 11.94###177.33 +- 45.57**

HbA1c (%)###N.A###5.79 +- 1.43

Insulin (IU/mL)###13.28 +- 5.26###37.08 +- 7.66**

Genotype and allele frequencies of the study subjects are given in Table-II. The genotyped variant showed a strong association with GDM (p<0.001). The rs2237895 C allele depicted a significant risk association with GDM (p<0.001).

Further, regression analysis was performed on unadjusted genotypes and after adjusting with risk factors such as age and pre pregnancy BMI. A significant association was observed with GDM (OR 2.281; p = 0.0002), which remained independently linked with GDM risk (OR 2.068; p=0.005) even after multiple comparison under additive model (Table-III).

We also investigated the association of KCNQ1 variant with quantitative traits associated with obesity and glucose homeostasis in the study cohort. Linear regression analysis revealed a moderately significant association of 'C' allele with insulin levels (b = -0.238 p = 0.0007), HbA1c (b = -0.123 p< 0.001) while weak association were seen with HOMA-IR (b = -0.021 p< 0.001) and fasting blood glucose (b = -0.043 p< 0.001).

Table-II: Genotypes and Allele Frequencies of KCNQ1 rs2237895 polymorphism.

###Genotype###Control (n=429)###Case (n=208)###P value###Allele###Group###Allele Data

###rs2237895###Frequency n (%)###OR (95%CI)###P value

###AA###175 (40.8)###51 (24.5)###<0.001###C###Control###320 (37.50)###1.557 (1.228-1.973)###< 0.001

###AC###188 (43.8)###114 (54.8)###Case###216 (51.92)

###CC###66 (15.4)###43 (20.7)###A###Control###538 (62.50)

###Case###200 (48.08)

Table-III: Association of KCNQ1 SNP with GDM assessed under Additive model.

###Unadjusted Odds Ratio###Adjusted for Age and BMI

###Genotype###Odds Ratios###95.0% C.I Odds Ratio###Odds Ratios###95.0% C.I Odds Ratio

###rs2237895###2.281**###1.388-3.746###2.068*###1.430-2.991

DISCUSSION

There are many proposed theories such as polymorphisms in PPAR2, IGF2BP2, CDKL1 and CDKN2a in the quest to find a link between genetic factors and GDM.7 Many studies have linked T2DM with polymorphisms in KCNQ1 gene.16,11,13,19 but few with GDM. We focused on rs2237895 SNP in the KCNQ1 gene which is known to be a susceptible T2DM candidate gene, and it showed a possible sound association with GDM in our study (Table II and III). Our findings are in line with the initial data on the link between KCNQ1 and GDM which came through studies done in Korean population. It was reported that the C allele of rs2237895 was associated with increased risk of GDM (OR=1.24; p=0.005).6,20,21 Similar results to our study were found in a Chinese population.22

We also report a risk allele frequency of 52% in GDM positive females, which is somewhat close to the risk allele frequency of 45% reported in Indian Punjabis with T2DM,13 35% in Chinese females with GDM,22 33% in Korean GDM females20 and 34.5% in Chinese subjects with T2DM.23

Similarly, the minor allele frequency reported in our study was 37.5% in our control population (Table-II), which is close to a previously published result of 42%.13 The difference in frequencies reported could be due to a different set of ethnic population at a different geographic location tested. A moderately significant association of 'C' allele with insulin levels, HbA1c, insulin resistance and fasting glucose levels was observed in our study similar to a previous report.13 Additionally, in two recent related studies for Pakistani population it was reported that SNPs in or near PPARG, TCF7L2, FTO, CDKN2A/2B, and KCNQ1 may have potential associations with T2DM, with similar effect sizes to those seen in European populations.6,24 Though, this is an exciting finding further research is required to establish an affirmative causal link.

We also observed that both weight and body mass index (BMI) values were higher in our GDM cases in comparison to controls (Table-I). Asian's are known to have a higher body fat proportion even at a lower BMI value in comparison to Caucasian's,26 and this situation might lead to early development of adverse effects during pregnancy. Though, we failed to identify any significant association in terms of weight and BMI with the minor allele in our study population. Despite the fact that weight of the baby is controlled by the anthropometric measures of the parents' via genetic bond, mother's weight has a supplementary effect, controlling the intrauterine environment. This suggests that KCNQ1 polymorphism may not have a direct impact on the weight status of an individual but act by other pathways to induce insulin resistance in GDM and/or T2DM.

The associations between KCNQ1 polymorphisms and increased risk for GDM not only indicate similar pathogenic mechanisms with T2DM but also make KCNQ1 a novel potential therapeutic target for both T2DM and GDM. Our study was limited in a way that we were unable to recruit large number of study participants due to cultural constraints about genetic studies. More so, we did not focus on the lifestyle factors or environmental factors, such as diet and physical activities, which prevents us from analysing any interaction between rs2237895 and other factors on GDM. Nevertheless, the rs2237895 polymorphism was in HWE in the both groups, suggesting the randomness of subject selection which is a strength of our study.

CONCLUSION

This study identifies that KCNQ1 rs2237895 polymorphisms might be associated with risk of GDM in Pakistani population and that it is related to the higher glucose levels and insulin resistance. Further large scale studies are required to consolidate on the functional aspect of this polymorphism.

Declaration of interest: The authors declare that they have no conflict of interest.

Funding: This study was funded by the Aga Khan University Seed Money Grant (PF30/1212).

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Publication:Pakistan Journal of Medical Sciences
Article Type:Medical condition overview
Date:Dec 31, 2016
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