A genetic analysis of type 2 (non-insulin-dependent) diabetes mellitus in Punjabi Sikhs and British Caucasoid patients

Association of the HLA-DQA1 and HLA-DQB1 Alleles in Type 2 Diabetes Mellitus and Diabetic Nephropathy in the Han Ethnicity of China

HLA gene system is one of the most polymorphic regions of the human genome. The association of HLA class II genes in T1DM pathogenesis has been reported for several ethnicities. Associations of HLA class II genes with T2DM have revealed inconsistent results. Moreover, correlations between DN and HLA alleles remain unclear. We carried out DNA typing chip by specific medium resolution typing probes in 310 T2DM subjects (including 210 patients with DN and 100 patients without DN) in addition to 100 healthy controls. Differences were found between patients with T2DM and the control group in the frequencies of the HLA-DQA1∗0301 (15.5% versus 8.0%, P < 0.01) and the HLA-DQA1∗0501 alleles (16.6% versus 8.5%, P < 0.01). Differences were found between patients with DN and without DN in the frequencies of the HLA-DQA1∗0302 (6.9% versus 13.5%, P < 0.01) and HLA-DQB1∗0501 alleles (5.8% versus 14.5%, P < 0.01). Diabetes duration and systolic blood pressure were independent risk factors associated with DN (OR = 2.277 and 1.366, resp., P < 0.05), whereas the HLA-DQB1∗0501 llele had a protective effect on DN (OR = 0.53, P < 0.05). These data suggest the HLA-DQA1∗0301 and HLA-DQA1∗0501 alleles are markers of susceptibility for T2DM, and the HLA-DQB1∗0501 allele is associated with a protective effect on DN in Han ethnicity of China.

Susceptible and protective human leukocyte antigen class II alleles and haplotypes in bahraini type 2 (non-insulin-dependent) diabetes mellitus patients

Whereas the genetic risk for type 1 diabetes is linked to human leukocyte antigen (HLA) class II genes, the HLA association in type 2 (non-insulin-dependent) diabetes is less clear. The association between HLA class II genotypes and type 2 diabetes was examined in adult Bahrainis, an Arab population with a high prevalence of type 2 diabetes. HLA-DRB1* and -DQB1* genotyping of 86 unrelated type 2 diabetes patients (age, 51.6+/-8.2 years; mean duration of diabetes, 7.7+/-7.1 years) who had a strong family history of diabetes (52 of 72 versus 0 of 89 for controls, P<0.001) and 89 healthy subjects was done by PCR-sequence-specific priming. DRB1*040101 (0.1221 versus 0.0562, P=0.019) and DRB1*070101 (0.2151 versus 0.0843, P<0.001) were positively associated, while DRB1*110101 (0.0698 versus 0.1461, P=0.014) and DRB1*160101 (0.0640 versus 0.1236, P=0.038) were negatively associated with type 2 diabetes. DRB1*040101-DQB1*0302 (0.069 versus 0.0007; P=0.004), DRB1*070101-DQB1*0201 (0.178 versus 0.0761, P=0.007), DRB1*070101-DQB1*050101 (0.125 versus 0.0310, P=0.002), and DRB1*150101-DQB1*060101 (0.0756 versus 0.0281, P=0.008) were more prevalent among patients, while DRB1*160101-DQB1*050101 (0.0702 versus 0.0349, P=0.05) was more prevalent among controls, conferring disease susceptibility or protection, respectively. In Bahrainis with type 2 diabetes, there is a significant association with select HLA class II genotypes, which were distinct from those in type 1 diabetes.

Associated risk factors of diabetes in Kin-Hu, Kinmen

This is a community-based survey carried out by the Yang-Ming Crusade to investigate potential risk factors of non-insulin-dependent diabetes in Kin-Hu, Kinmen. A total of 3236 people completed both questionnaire and venipuncture (1536 men and 1700 women). Sex, age, education level, family history, obesity, hypertension, triglyceride, cholesterol levels and usage of diuretics were found significantly correlated with diabetes in univariate analyses. The stepwise logistic regression was used in multivariate analysis. Important correlates were age (OR = 1.03; 95% CI, 1.02-1.05), body mass index (OR = 1.96; 95% CI, 1.31-2.94), waist/hip ratio (OR = 2.08; 95% CI, 1.38-3.13), triglyceride (OR = 1.47; 95% CI, 1.19-1.81), cholesterol (OR = 1.47; 95% CI, 1.23-1.77), HDL-cholesterol (OR = 0.50; 95% CI, 0.25-0.99) and previous hypertension (OR = 1.66; 95% CI, 1.05-2.61). In addition to body mass index, waist/hip ratio was an independent risk factor. Besides the risk factor of total cholesterol, HDL-cholesterol was an independent protective factor. Previous history of hypertension was a stronger predictor on diabetes than current hypertension.

Use of DNA polymorphisms for genetic analysis of non-insulin dependent diabetes mellitus

Polymorphisms occur on the average of one out of every 500 base pairs of DNA, and these polymorphisms provide useful markers for genetic analysis. Hundreds of RFLP markers have been mapped at regular intervals throughout the human genome. Diabetes genes have not been mapped with these markers, however, only one MODY family has been partially evaluated. This type of analysis is further complicated if NIDDM is multigenic and/or polygenic. RFLPs have been used to evaluate specific candidate loci for NIDDM, e.g. the insulin, insulin receptor and glucose transporter genes. For these analyses, population and family studies (limited in number) have suggested that none of these loci are major contributors to the genetic susceptibility to NIDDM. In no case, however, could a contribution of 10% or less of these loci be confidently excluded, because of variable penetrance, different degrees of linkage disequilibrium between RFLPs and putative mutations, the frequencies of the RFLPs in non-diabetic populations, and inadequate sample size. The conclusions are clear: either (1) the correct candidate gene(s) has not been found, or (2) sample sizes need to be increased by at least an order of magnitude, or (3) newer methods of analysis must be adopted (e.g. use of extended haplotypes and associations with subphenotypes, or screening with allele specific oligonucleotide probes, denaturing gradient gel electrophoresis or direct genomic sequencing of polymerase chain reaction amplified DNA).

Genetics of non-insulin dependent diabetes mellitus

It is probable that NIDDM has a multifactorial origin in which environmental factors hasten the progression of the disease in genetically predisposed individuals. The importance of the genetic contribution to NIDDM has been established by the study of certain inbred populations, the almost 100% concordance of disease in monozygotic twins and by familial clustering. However, progress in identifying specific genetic factors involved in NIDDM has been slow and no consistent evidence has emerged supporting a major aetiological role for any of the genes so far studied. This may be due in part to methodological problems encountered in the identification of such disease susceptibility genes.

Insulin receptor gene polymorphisms in type 2 (non-insulin-dependent) diabetes mellitus

The insulin receptor has been proposed as a candidate gene for the inherited defect in Type 2 (non-insulin-dependent) diabetes mellitus and we therefore studied three restriction fragment length polymorphic sites, two revealed with the enzyme Sst1 and one by Rsa1, using two insulin receptor cDNA probes in 131 Caucasian Type 2 diabetic patients and 94 control subjects. The frequency of the six alleles studied did not differ significantly between the two groups. However, one allele, a 6.2 kilobase Rsa1 fragment (R+), was found more frequently in those diabetic subjects (n = 48) with a positive family history of diabetes (R + frequency = 0.48) compared to those diabetic subjects (n = 63) with a negative family history (R + frequency = 0.34, p less than 0.05). These results suggest that this polymorphism may be a linkage marker for the genetic defect in a subgroup of Type 2 diabetic patients with a positive family history.

An analysis of amplified insulin gene products in diabetics of Indian origin

We have previously described an increased incidence of the class 3 allele of the hypervariable region (HVR) 5' to the insulin gene in south Indian non-insulin dependent diabetics; this association is absent in Punjabi Sikhs with this disorder. Using the polymerase chain reaction we have amplified parts of the insulin gene from 130 subjects to look for mutations which may be in linkage disequilibrium with the class 3 allele and hence explain its association with non-insulin dependent diabetes (NIDDM). In 23 south Indian subjects with NIDDM, using the restriction enzyme MboII, a B chain mutant (insulin Chicago) was excluded. Two patterns (alpha and beta) were found, representing a PstI polymorphism in the 3' untranslated region of the insulin gene. In subjects homozygous for the class 1 allele, the allelic frequency for alpha was 0.94 (143/152) and for beta was 0.06, in heterozygotes (1,3) alpha 0.63 (54/86) and beta 0.37, and in homozygotes for the class 3 allele alpha 0.18 (4/22) and beta 0.82 (p less than 0.001), thus establishing linkage disequilibrium between these two loci. No differences in allelic frequency were found in the south Indians or Punjabi Sikhs between controls and the different types of non-insulin requiring diabetes (NIDDM, fibrocalculous pancreatic diabetes and maturity onset diabetes of the young) when both groups were matched for insulin genotypes. Thus, although this polymorphism in the 3' untranslated region of the insulin gene is in linkage disequilibrium with the class 3 allele, it does not appear to be any better at predicting diabetes than the class 3 allele itself.