Impact of nine common type 2 diabetes risk polymorphisms in Asian Indian Sikhs: PPARG2 (Pro12Ala), IGF2BP2, TCF7L2 and FTO variants confer a significant risk.
BACKGROUND
Recent genome-wide association (GWA) studies have identified several unsuspected genes associated with type 2 diabetes (T2D) with previously unknown functions. In this investigation, we have examined the role of 9 most significant SNPs reported in GWA studies: [peroxisome proliferator-activated receptor gamma 2 (PPARG2; rs 1801282); insulin-like growth factor two binding protein 2 (IGF2BP2; rs 4402960); cyclin-dependent kinase 5, a regulatory subunit-associated protein1-like 1 (CDK5; rs7754840); a zinc transporter and member of solute carrier family 30 (SLC30A8; rs13266634); a variant found near cyclin-dependent kinase inhibitor 2A (CDKN2A; rs10811661); hematopoietically expressed homeobox (HHEX; rs 1111875); transcription factor-7-like 2 (TCF7L2; rs 10885409); potassium inwardly rectifying channel subfamily J member 11(KCNJ11; rs 5219); and fat mass obesity-associated gene (FTO; rs 9939609)].


METHODS
We genotyped these SNPs in a case-control sample of 918 individuals consisting of 532 T2D cases and 386 normal glucose tolerant (NGT) subjects of an Asian Sikh community from North India. We tested the association between T2D and each SNP using unconditional logistic regression before and after adjusting for age, gender, and other covariates. We also examined the impact of these variants on body mass index (BMI), waist to hip ratio (WHR), fasting insulin, and glucose and lipid levels using multiple linear regression analysis.


RESULTS
Four of the nine SNPs revealed a significant association with T2D; PPARG2 (Pro12Ala) [odds ratio (OR) 0.12; 95% confidence interval (CI) (0.03-0.52); p = 0.005], IGF2BP2 [OR 1.37; 95% CI (1.04-1.82); p = 0.027], TCF7L2 [OR 1.64; 95% CI (1.20-2.24); p = 0.001] and FTO [OR 1.46; 95% CI (1.11-1.93); p = 0.007] after adjusting for age, sex and BMI. Multiple linear regression analysis revealed significant association of two of nine investigated loci with diabetes-related quantitative traits. The 'C' (risk) allele of CDK5 (rs 7754840) was significantly associated with decreased HDL-cholesterol levels in both NGT (p = 0.005) and combined (NGT and T2D) (0.005) groups. The less common 'C' (risk) allele of TCF7L2 (rs 10885409) was associated with increased LDL-cholesterol (p = 0.010) in NGT and total and LDL-cholesterol levels (p = 0.008; p = 0.003, respectively) in combined cohort.


CONCLUSIONS
To our knowledge, this is first study reporting the role of some recently emerged loci with T2D in a high risk population of Asian Indian origin. Further investigations are warranted to understand the pathway-based functional implications of these important loci in T2D pathophysiology in different ethnicities.
Sanghera
Dharambir K
DK
Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA. Dharambir-Sanghera@ouhsc.edu
Ortega
Lyda
L
Han
Shizhong
S
Singh
Jairup
J
Ralhan
Sarju K
SK
Wander
Gurpreet S
GS
Mehra
Narinder K
NK
Mulvihill
John J
JJ
Ferrell
Robert E
RE
Nath
Swapan K
SK
Kamboh
Mohammed I
MI
D000328:Adult; D000368:Aged; D000071516:Alpha-Ketoglutarate-Dependent Dioxygenase FTO; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000235:genetics*; D005006:Ethnicity; D005260:Female; D005819:Genetic Markers; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D007194:India; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D047495:PPAR gamma / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D011506:Proteins / Q000235:genetics*; D012307:Risk Factors; D051820:TCF Transcription Factors / Q000235:genetics*; D058118:Transcription Factor 7-Like 2 Protein
D005819:Genetic Markers; D018971:Insulin-Like Growth Factor Binding Protein 2; D047495:PPAR gamma; D011506:Proteins; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D058118:Transcription Factor 7-Like 2 Protein; D000071516:Alpha-Ketoglutarate-Dependent Dioxygenase FTO; C526492:FTO protein, human