Hints of unique genetic effects for type 2 diabetes in India

Genetics of type 2 diabetes mellitus in Indian and Global Population: A Review

Background

Non-communicable diseases such as cardiovascular diseases, respiratory diseases and diabetes contribute to the majority of deaths in India. Public health programmes on non-communicable diseases (NCD) prevention primarily target the behavioural risk factors of the population. Hereditary is known as a risk factor for most NCDs, specifically, type 2 diabetes mellitus (T2DM), and hence, understanding of the genetic markers of T2DM may facilitate prevention, early case detection and management.

Main body

We reviewed the studies that explored marker-trait association with type 2 diabetes mellitus globally, with emphasis on India. Globally, single nucleotide polymorphisms (SNPs) rs7903146 of Transcription Factor 7-like 2 (TCF7L2) gene was common, though there were alleles that were unique to specific populations. Within India, the state-wise data were also taken to foresee the distribution of risk/susceptible alleles. The findings from India showcased the common and unique alleles for each region.

Conclusion

Exploring the known and unknown genetic determinants might assist in risk prediction before the onset of behavioural risk factors and deploy prevention measures. Most studies were conducted in non-representative groups with inherent limitations such as smaller sample size or looking into only specific marker-trait associations. Genome-wide association studies using data from extensive prospective studies are required in highly prevalent regions worldwide. Further research is required to understand the singular effect and the interaction of genes in predicting diabetes mellitus and other comorbidities.

Association of PGC-1α gene with type 2 diabetes in three unrelated endogamous groups of North-West India (Punjab): a case-control and meta-analysis study

PGC-1α (Peroxisome proliferator-activated receptor gamma, coactivator 1 alpha) plays a key role in glucose homeostasis inside liver and muscle. The impact of six polymorphisms of PGC-1α with Type 2 Diabetes (T2D) susceptibility was evaluated on 1125 samples comprising of 554 T2D cases and 571 controls among three endogamous groups (Bania, Brahmin and Jat Sikh) of North-West India (Punjab). Single-locus analysis showed a significant differential pattern of genetic association of PGC-1α among studied groups emphasizing the role of ethnicity towards disease susceptibility. Haplotypes G-A-G-G-C-C in Bania group; G-G-G-G-C-A in Brahmin; G-A-A-G-T-C, G-G-G-G-T-C in Jat Sikh groups conferred ~ two to fivefold increased T2D risk. Intriguingly, the haplotype combination G-A-G-G-C-C provided T2D risk in Banias whereas it played a protective role in Brahmins reflecting the role of ethnic heterogeneity. In the secondary structure prediction of mRNA, slight free energy change along with structural changes was observed between the wild and variant allele of rs3736265, rs8192678 and rs2970847 loci. Meta-analyses conducted on rs8192678 and rs2970847 variants illustrated the overall effect of minor alleles providing a higher risk for the T2D development. Divergence in genetic variants and haplotype combinations associated with T2D risk among studied groups is inferred from the present dataset, which strongly highlights the combinatorial effect of diverse ethnic background of the population under study with genetics towards susceptibility to complex diseases like T2D.

Distribution of CYP2C8 and CYP2C9 amino acid substitution alleles in South Indian diabetes patients: A genotypic and computational protein phenotype study

The CYP2C8 and CYP2C9 are two major isoforms of the cytochrome P450 enzyme family, which is involved in drug response, detoxification, and disease development. This study describes the differential distribution of amino acid substitution variants of CYP2C8 (*2-I269F & *3-R139K) and CYP2C9 (*2-C144R & *3-L359A) genes in 234 type 2 diabetes mellitus (T2DM) patients and 218 healthy controls from Andhra Pradesh, South India. Single locus genotype analysis has revealed that homozygous recessive genotypes of 2C8*2-TT (P ≤ .03), 2C9*2-TT (P ≤ .02), and heterozygous 2C9*3-AC (P ≤ .006) are seen to be increasingly present in the case group, indicating a significant level of their association with diabetes in Andhra population. The statistical significance of these recessive genotypes has persisted even under their corresponding allelic forms (P ≤ .01). Genotype association results were further examined by computational protein structure and stability analysis to assess the deleteriousness of the amino acid changes. The mutant CYP 2C8 and 2C9 (both *2 and *3) proteins showed structural drifts at both amino acid residue (range 0.43Å-0.77Å), and polypeptide chain levels (range 0.68Å-1.81Å) compared to their wild-type counterparts. Furthermore, the free energy value differences (range -0.915 to -1.38 Kcal/mol) between mutant and native protein structures suggests the deleterious and destabilizing potential of amino acid substitution polymorphisms of CYP genes. The present study confirms the variable distribution of CYP2C8 (*2 and *3) and CYP2C9 (*2 and *3) allelic polymorphisms among South Indian diabetic populations and further warrants the serious attention of CYP gene family, as a putative locus for disease risk assessment and therapy.

Diabetes in India: what is different?

PURPOSE OF REVIEW

The purpose of this study was to review the epidemiology and pathogenesis of diabetes in Asian Indians with a particular focus on 'Asian Indian type 2 diabetes phenotype'.

RECENT FINDINGS

The prevalence of diabetes is rapidly increasing among Asian Indians, particularly in the past two decades. The diabetes rates in urban India now exceed that seen in Indians migrated to developed nations. Urbanization, changes from traditional healthier diets to high-refined carbohydrate intake, and sedentary lifestyle have contributed to this steep increase in the prevalence of diabetes in India. Type 2 diabetes among Asian Indians is characterized by onset at a younger age, greater abdominal obesity despite relatively lower BMI, greater insulin resistance, and early decline in beta cell function. Asian Indians are also at a higher risk for premature coronary artery disease.

SUMMARY

The clinical profile of type 2 diabetes in Asian Indians differs from Caucasians with higher central obesity, increased inflammatory markers such as high sensitive C-reactive protein, greater insulin resistance, early loss of beta cell function, and a higher risk of coronary artery disease. Mechanistic studies are needed to characterize the pathophysiology of the Asian Indian phenotype.

GLP-1(28-36)amide, a Long Ignored Peptide Revisited

Glucagon-like peptide-1 (GLP-1), which has been extensively applied for treating type 2 diabetes mellitus (T2DM), is an incretin hormone that regulates glucose homeostasis. GLP-1(28-36)amide, a C-terminal nonapeptide (FIAWLVKGRamide) of GLP-1, is a major product derived from the cleavage of GLP-1 by the neutral endopeptidase (NEP). GLP-1(28-36)amide has long been regarded as a metabolically inactive byproduct, however, recent findings reveal that GLP-1(28-36)amide plays multiple novel roles in ameliorating hepatic metabolism, protecting β cells, improving glucose disposal and inhibiting weight gain. Here, we summarize the latest progress on the effects of GLP-1(28-36)amide with a focus on its roles in regulating the Wnt and mitochondrial-mediated signaling pathways.

Is vulnerability to cardiometabolic disease in Indians mediated by abdominal adiposity or higher body adiposity

Background

Indians may be particularly vulnerable to cardiometabolic disease, potentially due to higher body fat for a given BMI, or a tendency towards depositing abdominal adiposity. The aim of the study is to assess whether different measures of the distribution of adiposity (abdominal versus whole body) or amount of adiposity (DXA versus traditional anthropometric) are better at predicting prevalent cardiometabolic risk markers in an Indian population.

Methods

Participants were recruited from the Indian Migration Study (IMS) and the Andhra Pradesh Children and Parent Study (APCAPS). Participants attended a clinic in Hyderabad, India, January 2009-December 2010. Adiposity was measured by conventional anthropometry (including weight, height, waist) and DXA scanning (whole body and abdominal). Blood samples were taken and assessed for fasting plasma glucose, insulin, cholesterol, and triglycerides and blood pressure was measured. Lifestyle data were collected by questionnaire.

Results

We invited 4 617 participants to the clinic (1 995 IMS; 2 622 APCAPS) and examined 918 from IMS (46%) and 1 451 from APCAPS (55%). There were strong and consistent relationships between adiposity and cardiometabolic risk factors. Cardiometabolic risk factors did not appear to be more strongly associated with DXA measures as opposed to BMI, or skinfold measures of body fat. There was some evidence that WHR was more closely related to diabetes than total body adiposity, but this was not apparent for the other measures of abdominal adiposity (DXA measures, waist circumference) or other cardiometablic risk factors.

Conclusions

No strong evidence supports that DXA measures or abdominal measures of adiposity are better at predicting the prevalence of cardiometabolic risk factors in comparison to BMI.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2458-14-1239) contains supplementary material, which is available to authorized users.