Association of Vitamin D Deficiency and Vitamin D Receptor Gene Polymorphisms with Type 1 Diabetes Risk: A South Indian Familial Study

Objective: Vitamin D is a potent immune modulator and is associated with autoimmune diseases, including type 1 diabetes (T1D). The vitamin D levels and its receptor gene polymorphisms together in T1D are not yet investigated in the South Indian population. The present study focused on exploring the significance of vitamin D levels and vitamin D receptor (VDR) gene polymorphisms with the risk of developing T1D in the South Indian population. Methods: Patients with T1D and unaffected first-degree relatives (FDRs) were included in this study. Genotyping of VDR polymorphisms at four different loci (FokI- F/f, BsmI- B/b, TaqI- T/t, and ApaI- A/a) was assessed through the amplification refractive mutation system-polymerase chain reaction method. Serum vitamin D levels were measured in 98 T1D patients and 75 age- and sex-matched siblings. Results: A total of 120 patients with T1D and 214 FDRs were included. Vitamin D deficiency (VDD) was observed in a higher proportion of T1D patients than in controls (52% vs. 32%; p<0.03). The frequency of the FokI-FF genotype was significantly higher [odds ratio (OR)=1.66; p<0.03] in T1D patients conferring a susceptible association with the disease. Nevertheless, the increased frequency of heterozygous Ff genotype (OR=0.57; p<0.02) among controls may confer a protective association with T1D. Furthermore, the transmission disequilibrium test revealed over-transmission of ApaI-A (T: U=15/5; p<0.006) and BsmI-B alleles (T: U=17/5; p<0.01) and under-transmission of BsmI-b/ApaI-a/TaqI-T haplotype (T: U=5.4/14.4; p=0.04) from parents to T1D patients. Conclusion: The present study concludes that VDD is the major contributing risk factor to T1D development in the South Indian population. Furthermore, the FokI-FF genotype, BsmI-B, and ApaI-A alleles were positively associated with T1D. In contrast, the FokI-Ff genotype and BsmI-b/ApaI-a/TaqI-T haplotype were negatively associated with T1D.

Evaluation of HLA-G 14bp Ins/Del and +3142 C/G Polymorphisms in Type 1 Diabetes among South Indian Population.

Background: Type 1 diabetes (T1D) is a multifactorial autoimmune disease, involving strong genetic components with familial predisposition. Human leukocyte antigen-G (HLA-G) is a non-classical HLA-class I molecule having several immunomodulatory functions. Polymorphisms in HLA-G are associated with several autoimmune diseases including T1D. This study aims to evaluate the association of HLA-G 14bp Ins/Del and +3142 C/G polymorphisms with T1D among the South Indian population. Methods: The study was performed in a cohort of 123 T1D patients along with their 51 siblings and 126 parents. The association and linkage of HLA-G 14bp Ins/Del and +3142 C/G polymorphisms with T1D were analysed, and transmission disequilibrium test (TDT) was performed. Results: Significantly increased frequencies of HLA-G 14bp Del/Del genotype (OR = 2.16, pc = 0.0302) and Del allele (OR = 1.71, pc = 0.0398) were observed in female patients compared to parents. Higher frequencies of DelDel/GG combined genotype (OR = 4.45, pc = 0.0049) and Del/G haplotype (OR = 2.91, pc = 0.0277) were observed in female patients compared to parents. TDT also revealed over-transmission of Del/G haplotype (25T vs 7UT; P = 0.0015) and a strong linkage disequilibrium between the studied polymorphisms. Conclusion: This familial study shows the association of HLA-G 3'UTR 14bp Ins/Del polymorphism with the risk of T1D among the South Indian population, especially in females.

Association of Killer Cell Immunoglobulin-Like Receptors and Their HLA-Ligands with Type 1 Diabetes Among South Indian Population.

BACKGROUND: Type 1 diabetes (T1D) is a multifactorial autoimmune disease, involving strong genetic components with familial predisposition. Killer cell immunoglobulin-like receptors (KIRs) found on the surface of NK cells have ligands of human leukocyte antigen (HLA) class I that are associated with T1D. The present study evaluates the influence of KIR genes and their HLA-ligands in the aetiology of T1D among the South Indian population. METHODS: A total of 125 T1D patients, along with their parents (n = 126) and siblings (n = 52) were recruited. PCR-based genotyping was performed for KIR genes and HLA class I ligands. The gene frequencies were compared between patients and siblings/parents. Linkage-disequilibrium (LD) analysis was performed to assess the genetic association between KIR gene pairs. RESULTS: The results show significant differences in HLA-ligands of KIR genes between patients and parents. The HLA-C1C1 homozygosity was found to be a predisposing risk factor, and HLA-C1C2 heterozygosity was protective towards T1D along with either the activating KIR2DS2 or inhibitory KIRs 2DL1, 2DL2, 2DL3. However, the frequency of inhibitory KIR3DL1 significantly increased in the presence of HLA-B Bw4 Ile80 in parents when compared to patients showing a protective effect on T1D. Two pairs of KIR genes, 2DS4-3DL1 and 2DS1-2DL5, showed strong LD in patients, siblings and parents. CONCLUSION: The KIR-HLA ligand combinations have a significant effect on T1D aetiology among the South Indian population. This study defines a pattern for family-based association studies with genotypic information about KIR genes and their HLA-ligands, providing the first evidence towards T1D among the South Indian population.

Association of CTLA-4 and CD28 Gene Polymorphisms with Type 1 Diabetes in South Indian Population.

Each functional gene illustrates the complexity of genetic predisposition to disease; however, it is difficult to bring out these traits with reference to autoimmune diseases like type 1 diabetes (T1D). To find out the genetic contribution of CTLA-4 + 49A/G, CTLA-4 -318C/T and CD28 + 17T/C polymorphisms toward T1D, the present study was performed with 124 T1D patients, 54 siblings and 125 parents including 39 trios in South Indian population. The association and linkage of CTLA-4 + 49A/G, CTLA-4 -318C/T and CD28 + 17T/C polymorphisms with T1D were analyzed and transmission disequilibrium test was performed. CTLA-4 G allele carrying genotypes (GG+AG) showed a higher risk association and can be considered as susceptible to develop T1D among patients with age at diagnosis from 0 to 10 years as compared to siblings (OR = 2.9; pc = 0.047) and parents (OR = 2.7; pc = 0.036). On the other hand, a strong protection against the disease (age at diagnosis; 0-10 years) was observed with CTLA-4 + 49AA genotype (OR = 0.37; pc = 0.036) and combined AA/CC genotype (OR = 0.31; pc = 0.034) of CTLA-4 + 49A/G and CTLA-4 -318C/T polymorphisms. However, a significant association was not observed between CTLA-4 -318C/T and CD28 + 17T/C polymorphisms and T1D. This family-based study reports a strong association between possible genotypes of CTLA-4 gene polymorphism and T1D in South Indian population, particularly in younger individuals.

SLC30A8 Gene rs13266634 C/T Polymorphism in Children with Type 1 Diabetes in Tamil Nadu, India

Objective: Zinc transporter 8 (ZnT8) is a multi-transmembrane protein situated in the insulin secretory granule of the islets of ß-cells and is identified as a novel auto-antigen in type 1 diabetes (T1D). The gene coding for ZnT8, solute carrier family 30 member 8 (SLC30A8) is located on chromosome 8q24.11. This study aimed to identify the association of SLC30A8 rs13266634 C/T gene polymorphism with T1D in a sample of T1D children in Tamil Nadu, India. Methods: The family based study was conducted in 121 T1D patients and 214 of their family members as controls. The SLC30A8 gene rs13266634 C/T polymorphism was evaluated by polymerase chain reaction-restriction fragment length polymorphism. Results: No significant differences were observed in either allele (odds ratio: 0.92; confidence interval: 0.33-2.58; p=0.88) and genotype (CC: p=0.74; CT: p=0.82; TT: p=0.80) frequencies of rs13266634 C/T between T1D patients and controls. Transmission disequilibrium test has identified over-transmission of mutant T allele from parents to affected children (T: U=9:7) without statistical significance. Metaanalysis on the overall effects of rs13266634 C allele frequency was not different (p=0.10 and Pheterogeneity=0.99) in T1D patients as compared to the controls. Conclusion: The present study along with the meta-analysis does not show any substantial association of the rs13266634 C/T polymorphism with T1D development in this population.