Reassessment of the putative role of BLK-p.A71T loss-of-function mutation in MODY and type 2 diabetes.

AIMS/HYPOTHESIS: MODY is believed to be caused by at least 13 different genes. Five rare mutations at the BLK locus, including only one non-synonymous p.A71T variant, were reported to segregate with diabetes in three MODY families. The p.A71T mutation was shown to abolish the enhancing effect of BLK on insulin content and secretion from pancreatic beta cell lines. Here, we reassessed the contribution of BLK to MODY and tested the effect of BLK-p.A71T on type 2 diabetes risk and variations in related traits. METHODS: BLK was sequenced in 64 unelucidated MODY samples. The BLK-p.A71T variant was genotyped in a French type 2 diabetes case-control study including 4,901 cases and 4,280 controls, and in the DESIR (Data from an Epidemiological Study on the Insulin Resistance Syndrome) and SUVIMAX (Supplementation en Vitamines et Mineraux Antioxydants) population-based cohorts (n = 6,905). The variant effects were assessed by logistic and linear regression models. RESULTS: No rare non-synonymous BLK mutations were found in the MODY patients. The BLK p.A71T mutation was present in 52 normoglycaemic individuals, making it very unlikely that this loss-of-function mutation causes highly penetrant MODY. We found a nominal association between this variant and increased type 2 diabetes risk, with an enrichment of the mutation in the obese diabetic patients, although no significant association with BMI was identified. CONCLUSIONS/INTERPRETATION: No mutation in BLK was found in our MODY cohort. From our findings, the BLK-p.A71T mutation may weakly influence type 2 diabetes risk in the context of obesity; however, this will require further validation.

European genetic variants associated with type 2 diabetes in North African Arabs.

AIMS: Recent genome-wide association studies (GWAS) and previous approaches have identified many genetic variants associated with type 2 diabetes (T2D) in populations of European descent, but their contribution in Arab populations from North Africa is unknown. Our study aimed to validate these markers and to assess their combined effects, using large case-control studies of Moroccan and Tunisian individuals. METHODS: Overall, 44 polymorphisms, located at 37 validated European loci, were first analyzed in 1055 normoglycaemic controls and 1193 T2D cases from Morocco. Associations and trends were then assessed in 942 normoglycaemic controls and 1446 T2D cases from Tunisia. Finally, their ability to discriminate cases from controls was evaluated. RESULTS: Carrying a genetic variant in BCL11A, ADAMTS9, IGF2BP2, WFS1, CDKAL1, TP53INP1, CDKN2A/B, TCF7L2, KCNQ1, HNF1A, FTO, MC4R and GCK increased the risk of T2D when assessing the Moroccan and Tunisian samples together. Each additional risk allele increased the susceptibility for developing the disease by 12% (P = 9.0 × 10(-9)). Genotype information for 13 polymorphisms slightly improved the classification of North Africans with and without T2D, as assessed by clinical parameters, with an increase in the area under the receiver operating characteristic curve from 0.64 to 0.67 (P = 0.004). CONCLUSION: In addition to TCF7L2, 12 additional loci were found to be shared between Europeans and North African Arabs. As for Europeans, the reliability of genetic testing based on these markers to determine the risk for T2D is low. More genome-wide studies, including next-generation sequencing, in North African populations are needed to identify the genetic variants responsible for ethnic disparities in T2D susceptibility.

Variants within the calpain-10 gene and relationships with type 2 diabetes (T2DM) and T2DM-related traits among Tunisian Arabs.

BACKGROUND: Common variations in the calpain 10 (CAPN10) gene variants UCSNP-43, UCSNP-19 and UCSNP-63, and the 112/121 diplotype, are associated with an increased risk of type 2 diabetes (T2DM) and T2DM-related traits. METHODS: The association of UCSNP-43, -19 and -63 CAPN10 SNPs with T2DM was assessed in 917 Tunisian T2DM patients and 748 ethnically matched non-diabetic controls. CAPN10 genotyping was done by PCR-RFLP. RESULTS: Significant differences in UCSNP-19 MAF, but not UCSNP-43 or -63, and genotype distribution were seen between patients and controls. Heterogeneity in UCSNP-19, but not UCSNP-43 and -63, genotype distribution was noted according to geographical origin. Obesity was associated with UCSNP-19, while raised fasting glucose was associated with UCSNP-63, and increased HDL was associated with UCSNP-43. Enrichment of homozygous UCSNP-19 2/2 was seen in overweight and obese compared with lean patients; logistic-regression analyses demonstrated a positive association of the 2/2 genotype with overweight [P=0.003; OR (95% CI)=2.07 (1.28-3.33)] and obese [P=0.021; OR (95% CI)=1.83 (1.10-3.07)] patients. Of the six CAPN10 haplotypes identified, significant enrichment of only haplotype 111 was seen in T2DM patients [Pc=0.034; OR (95% CI)=1.22 (1.06-1.41)], while the frequency of all identified CAPN10 diplotypes, including the high-risk 112/121, was comparable between patients and controls. CONCLUSION: While CAPN10 UCSNP-19 SNP and haplotype 111 contribute to the risk of T2DM in Tunisian subjects, no significant association between CAPN10 diplotypes and T2DM was demonstrated.

Diabetic retinopathy, PAI-1 4G/5G and -844G/A polymorphisms, and changes in circulating PAI-1 levels in Tunisian type 2 diabetes patients.

AIM: The association of altered plasminogen activator inhibitor (PAI)-1 levels and PAI-1 polymorphisms (4G/5G and -844G/A) with diabetic retinopathy (DR) was investigated in 856 type 2 diabetes (T2D) patients, of whom 383 presented with (DR group), and 473 presented without (DWR group), retinopathy. METHODS: PAI-1 4G/5G and -844G/A genotyping were done by PCR-RFLP, and PAI-1 levels were measured by ELISA testing. RESULTS: The genotype distribution of 4G/5G and -844G/A polymorphisms did not deviate from the Hardy-Weinberg equilibrium model among healthy subjects. Higher frequencies of the 4G/4G genotype, and lower frequencies of the -844A allele, -844G/A and -844A/A genotypes, were seen in DR patients, conferring disease susceptibility and protection, respectively. While PAI-1 levels were significantly elevated in the 4G/4G compared with other PAI-1 genotypes, significant differences in PAI-1 levels between DR and DWR patients were seen in the 4G/-844A, 4G/-844G and 5G/-844A haplotype carriers among DR patients. However, comparable distributions of 4G/5G and -844G/A alleles, genotypes and haplotypes, and similar PAI-1 levels, were seen in the proliferative retinopathy (PR) and non-proliferative retinopathy (NPR) patients, indicating that neither PAI-1 variants nor changes in PAI-1 levels were linked to DR severity. Multivariate analyses identified 4G/-844A and 4G/-844G haplotypes as negatively and positively associated, respectively, with DR, but not with DR severity (PR vs NPR) after adjusting for a number of covariates. CONCLUSION: The present study identifies changes in PAI-1 levels and genetic variations at the PAI-1 locus as risk factors for DR, but not DR severity, that may serve as useful markers of increased DR susceptibility.

Association of the peroxisome proliferator-activated receptor-gamma2 Pro12Ala but not the C1431T gene variants with lower body mass index in Type 2 diabetes.

The peroxisome proliferator-activated receptor-gamma (PPARgamma) is a nuclear receptor involved in lipid metabolism, adipocyte differentiation and regulation of insulin sensitivity, and is associated with Type 2 diabetes (T2DM). The association of the C1431T silent mutation and the Pro12Ala missense transversion within the PPARgamma gene with the development of T2DM or obesity has often yielded contradictory results. We examined the association of the PPARgamma Pro12Ala and C1431T gene variants and their haplotypes with the susceptibility to T2DM. This was a retrospective study involving 491 T2DM patients and 400 age- and gender-matched controls. Pro12Ala and C1431T genotyping was done by PCR-RFLP analysis. Comparable frequencies of the mutant 12Ala (0.07 vs 0.08, p=0.216) and 1431T (0.12 vs 0.10, p=0.189) alleles, and Pro12Ala (p=0.218) and C1431T (p=0.421) genotypes were seen between patients and in nondiabetic control subjects. While no difference was noted in the distribution of Pro12Ala- C1431T haplotypes and genotypes between patients and controls, the PPARgamma 12Ala, but not 1431T, allele was significantly associated with lower body mass index (BMI) (< or =25.0) among patients. Regression analysis confirmed the association of the Pro12Ala (odds ratio =5.340; 95% confidence interval =1.044-27.311) with normal (BMI<25.0) but not with overweight/obesity among T2DM patients. Despite its association with lower BMI among T2DM patients, the PPARgamma gene does not appear to markedly influence Type 2 diabetes among Tunisian subjects.