A replication study of 49 Type 2 diabetes risk variants in a Punjabi Pakistani population

Assessment of genetic risk of type 2 diabetes among Pakistanis based on GWAS-implicated loci

Genome-wide association studies (GWAS) have identified multiple type 2 diabetes (T2D) loci, mostly among populations of European descent. There is a high prevalence of T2D among Pakistanis. Both genetic and environmental factors may be responsible for this high prevalence. In order to understand the shared genetic basis of T2D among Pakistanis and Europeans, we examined 77 genome-wide significant variants previously implicated among European populations. We genotyped 77 single-nucleotide polymorphisms (SNPs) by iPLEX® Gold or TaqMan® assays in a case-control sample of 1,683 individuals. Association analysis was performed using logistic regression. A total of 16 SNPs (TCF7L2/rs7903146, GLIS3/rs7041847, CHCHD9/rs13292136, PLEKHA1/rs2292626, FTO/rs9936385, CDKAL1/rs7756992, KCNJ11/rs5215, LOC105372155/rs12970134, KCNQ1/rs163182, CTRB1/rs7202877, ST6GAL1/rs16861329, ADAMTS9-AS2/rs6795735, LOC105370275/rs1359790, C5orf67/rs459193, ZBED3-AS1/rs6878122 and UBE2E2/rs7612463) showed statistically significant associations after controlling for the false discovery rate. While KCNQ1/rs163182 and ZBED3-AS1/rs6878122 showed opposite allelic effects, the remaining significant SNPs had the same allelic effects as reported previously. Our data indicate that a selected number of T2D loci previously identified among populations of European descent also affect the risk of T2D in the Pakistani population.

Association of HLA-B Gene Polymorphisms with Type 2 Diabetes in Pashtun Ethnic Population of Khyber Pakhtunkhwa, Pakistan

Human leukocyte antigen (HLA) system is the most polymorphic and gene dense region of human DNA that has shown many disease associations. It has been further divided into HLA classes I, II, and III. Polymorphism in HLA class II genes has been reported to play an important role in the pathogenesis of type 1 diabetes (T1D). It also showed association with T2D in different ethnic populations. However, a little is known about the relationship of HLA class I gene polymorphism and T2D. This study has evaluated the association of HLA-B (class I gene) variants with T2D in Pashtun ethnic population of Khyber Pakhtunkhwa. In the first phase of the study, whole exome sequencing (WES) of 2 pooled DNA samples was carried out, and DNA pools used were constructed from 100 diabetic cases and 100 control subjects. WES results identified a total of n = 17 SNPs in HLA-B gene. In the next phase, first 5 out of n = 17 reported SNPs were genotyped using MassARRAY® system in order to validate WES results and to confirm association of selected SNPs with T2D. Minor allele frequencies (MAFs) and selected SNPs×T2D association were determined using chi-square test and logistic regression analysis. The frequency of minor C allele was significantly higher in the T2D group as compared to control group (45.0% vs. 13.0%) (p = 0.006) for rs2308655 in HLA-B gene. No significant difference in MAF distribution between cases and controls was observed for rs1051488, rs1131500, rs1050341, and rs1131285 (p > 0.05). Binary logistic regression analyses showed significant results for SNP rs2308655 (OR = 2.233, CI (95%) = 1.223-4.077, and p = 0.009), while no considerable association was observed for the other 4 SNPs. However, when adjusted for these variants, the association of rs2308655 further strengthened significantly (adjusted OR = 7.485, CI (95%) = 2.353-23.812, and p = 0.001), except for rs1131500, which has no additive effect. In conclusion, the finding of this study suggests rs2308655 variant in HLA-B gene as risk variant for T2D susceptibility in Pashtun population.

KCNQ1 rs2237895 polymorphism is associated with Gestational Diabetes in Pakistani Women

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 was considered significant.

Results:

The variant genotyped was in Hardy-Weinberg equilibrium (p>0.05). The rs2237895 showed an association with GDM (OR 2.281; 1.388-3.746: p <0.001) and remained significant after multiple adjustments for age and body mass index (OR 2.068; 1.430-2.997: p=0.005). The C allele showed positive association with insulin level, and HOMA-IR in study subjects.

Conclusions:

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