Studying progression from glucose intolerance to type 2 diabetes in obese children.

AIM: Identification of metabolic and genetic factors capable to mediate progression from normal glucose tolerance (NGT) through impaired glucose tolerance (IGT) to type 2 diabetes (T2D) in childhood obesity. PATIENTS AND METHODS: Three groups of obese children with NGT (n=54), IGT (n=35), and T2D (n=62) were evaluated. A control group of non-obese normal children (n=210) was also studied. In obese patients, an oral glucose tolerance test (OGTT) was performed. Insulin resistance (IR) was assessed using HOMA-IR index. Insulin sensitivity (IS) was assessed according to the Matsuda formula. Genomic DNA from obese and control children was genotyped for genetic variants of PPARG, ADIPOQ, ADIPOR1, FTO, TCF7L2, and KCNJ11 using a real-time PCR strategy. The unpaired Student's t-test and Kruskal-Wallis one-way test were used to compare quantitative data in two and more groups. To assess the extent to which the various genetic variants were associated with pathology, ORs (odds ratios) and 95% CI (confidence interval) were estimated. RESULTS: In T2D children, HOMA-IR value (7.5±3.1) was significantly (P<0.001) higher than that in IGT (4.21±2.25) and NGT (4.1±2.4) subjects. The Matsuda IS index was significantly increased in normoglycemic patients compared to IGT individuals (2.8±1.75 vs. 2.33±1.2, P<0.05). The Pro12Ala polymorphism of PPARG was significantly associated with obesity (OR=1.74, 95% CI=1.19-2.55, P=0.004) and T2D in obesity (OR=2.01, 95% CI=1.24-3.26, P=0.004). CONCLUSION: IR is a major risk factor that mediates progression from NGT to clinical T2D in Russian obese children. This progression may be genetically influenced by the Pro12Ala variant of PPARG.

The carriage of the type 1 diabetes-associated R262W variant of human LNK correlates with increased proliferation of peripheral blood monocytes in diabetic patients.

OBJECTIVE: Lymphocyte adaptor protein (LNK) plays a pivotal role as a suppressor of T-cell receptor-mediated immune signaling and negative regulator of lymphopoiesis and early hematopoiesis. Recently, association between the R262W (c.784T>C) variant of the SH2B3 gene (rs3184504) encoding human LNK and type 1 diabetes (T1D) was found in several populations. In this study, we aimed to check whether this marker is associated with T1D in a Russian population. METHODS: Using a Taqman allele discrimination assay, we genotyped 1062 unrelated Russian individuals with diabetes at childhood and adolescence onset and 1020 healthy controls. T-cell proliferation assay based on the measurement of incorporation of bromo-2'-deoxyuridine incorporation into newly synthesized DNA was used to evaluate whether carriage of SH2B3 784T>C correlates with T-cell proliferation in patients' peripheral mononuclear blood cells (PMBCs) stimulated with anti-CD28 and anti-CD3 antibodies. RESULTS: The allele 784C of SH2B3 was related to a higher risk of T1D (odds ratio of 1.52, p = 1.2 × 10(-12)). A correlation between the carriage of the predisposing C/C variant of LNK and increased proliferation of T lymphocytes was shown in PMBCs of both diabetic [C/C vs. C/T vs.T/T = optical density at 450 nm (OD(450)) 6.3 ± 0.8 vs. 4.4 ± 0.7 vs. 2.7 ± 0.5, p = 0.0007] and non-diabetic (C/C vs. C/T vs.T/T = OD(450) 2.9 ± 0.6 vs. 2.2 ± 0.4 vs. 1.7 ± 0.4, p = 0.022) patients. CONCLUSIONS: The SH2B3 784T>C variant could contribute to the pathogenesis of T1D through impaired immune response that promotes activation and expansion of self-reactive lymphocytes in susceptible individuals.

The TAF5L gene on chromosome 1q42 is associated with type 1 diabetes in Russian affected patients.

Type 1 diabetes (T1D) is a multifactorial autoimmune disease, with strong genetic component. Several susceptibility loci contribute to genetic predisposition to T1D. One of these loci have been mapped to chromosome 1q42 in UK and US joined affected family data sets but needs to be replicated in other populations. In this study, we evaluated sixteen microsatellites located on 1q42 for linkage with T1D in 97 Russian affected sibling pairs. A 2.7-cm region of suggestive linkage to T1D between markers D1S1644 and D1S225 was found by multipoint linkage analysis. The peak of linkage was shown for D1S2847 (P = 0.0005). Transmission disequilibrium test showed significant undertransmission of the 156-bp allele of D1S2847 from parents to diabetic children (28 transmissions vs. 68 nontransmissions, P = 0.043) in Russian affected families. A preferential transmission from parents to diabetic offspring was also shown for the T(-25) and T1362 alleles of the C/T(-25) and C/T1362 dimorphisms, both located at the TAF5L gene, which is situated 103 kb from D1S2847. Together with the A/C744 TAF5L SNP, these markers share common T(-25)/A744/T1362 and C(-25)/C744/T1362 haplotypes associated with higher and lower risk of diabetes (Odds Ratio = 2.15 and 0.62, respectively). Our results suggest that the TAF5L gene, encoding TAF5L-like RNA polymerase II p300/CBP associated factor (PCAF)-associated factor, could represent the susceptibility gene for T1D on chromosome 1q42 in Russian affected patients.

Lack of association between genetic markers on chromosome 16q22-Q24 and type 1 diabetes in Russian affected families.

AIM: To evaluate whether the T1D susceptibility locus on chromosome 16q contributes to the genetic susceptibility to T1D in Russian patients. METHOD: Thirteen microsatellite markers, spanning a 47-centimorgan genomic region on 16q22-q24 were evaluated for linkage to T1D in 98 Russian multiplex families. Multipoint logarithm of odds (LOD) ratio (MLS) and nonparametric LOD (NPL) values were computed for each marker, using GENEHUNTER 2.1 software. Four microsatellites (D16S422, D16S504, D16S3037, and D16S3098) and 6 biallelic markers in 2 positional candidate genes, ICSBP1 and NQO1, were additionally tested for association with T1D in 114 simplex families, using transmission disequilibrium test (TDT). RESULTS: A peak of linkage (MLS=1.35, NPL=0.91) was shown for marker D16S750, but this was not significant (P=0.18). The subsequent linkage analysis in the subset of 46 multiplex families carrying a common risk HLA-DR4 haplotype increased peak MLS and NPL values to 1.77 and 1.22, respectively, but showed no significant linkage (P=0.11) to T1D in the 16q22-q24 genomic region. TDT analysis failed to find significant association between these markers and disease, even after the conditioning for the predisposing HLA-DR4 haplotype. CONCLUSION: Our results did not support the evidence for the susceptibility locus to T1D on chromosome 16q22-24 in the Russian family data set. The lack of association could reflect genetic heterogeneity of type 1 diabetes in diverse ethnic groups.

Evaluation of IDDM8 susceptibility locus in a Russian simplex family data set.

Type 1 diabetes (T1D) susceptibility locus, IDDM8, has been accurately mapped to 200 kilobases at the terminal end of chromosome 6q27. This is within the region which harbours a cluster of three genes encoding proteasome subunit beta 1 (PMSB1), TATA-box binding protein (TBP) and a homologue of mouse programming cell death activator 2 (PDCD2). In this study, we evaluated whether these genes contribute to T1D susceptibility using the transmission disequilibrium test of the data set from 114 affected Russian simplex families. The A allele of the G/A1180 single nucleotide polymorphism (SNP) at the PDCD2 gene, which was significant in its preferential transfer from parents to diabetic children (75 transmissions vs. 47 non-transmissions, chi2=12.85, P corrected=0.0038), was found to be associated with T1D. G/A1180 dimorphism and two other SNPs, C/T771 TBP and G/T(-271) PDCD2, were shown to share three common haplotypes, two of which (A-T-G and A-T-T) have been associated with higher development risk of T1D. The third haplotype (G-T-G) was related to having a lower risk of disease. These findings suggest that the PDCD2 gene is a likely susceptibility gene for T1D within IDDM8. However, it was not possible to exclude the TBP gene from being another putative susceptibility gene in this region.