S.-R. Li

Association between a restriction fragment length polymorphism at the liver/islet cell (GluT 2) glucose transporter and familial Type 2 (non-insulin-dependent) diabetes mellitus

SummaryPatients with Type 2 (non-insulin-dependent) diabetes mellitus and a strong family history of the disease may represent a sub-group where genetic factors play a pree-minent role in transmission of the disease. A defect in the liver/islet cell glucose transporter (GluT 2) could explain many of the pathophysiological features of the disease. In order to test the hypothesis that genetic variation at the GluT 2 locus contributes genetic susceptibility to Type 2 diabetes, 60 unrelated Caucasian diabetic patients with at least one affected sibling were genotyped for a Taq 1 restriction fragment length polymorphism marker. Hybridisation with a cDNA GluT 2 probe identified two alleles of sizes 13 kilobase (T1) and 19 kilobase (T2). The allele frequencies in the diabetic group with a family history were significantly different from those in a racially-matched control population of 122 subjects with no personal or family history of the disease (diabetic patients T1=0.96, T2=0.04, control subjects T1=0.89, T2=0.11, p< 0.03). However, when the study was repeated with 54 diabetic patients with indeterminate family history, statistical significance was not reached although the allele frequencies showed a similar trend. The findings of this study support the hypothesis that a genetic variant of the liver/islet cell glucose transporter may contribute to familial susceptibility in Type 2 diabetes.

Genetic polymorphisms at the human liver/islet glucose transporter (GLUTT2) gene locus in Caucasian and West Indian subjects with type 2 (non-insulin-dependent) diabetes mellitus

The liver/islet glucose transporter (GLUT2) is mainly expressed in the hepatocytes of the liver and the beta-cells of the pancreatic islets and a defect in this transporter could lead to diabetic phenotypes, such as relative hypoinsulinaemia and reduced uptake and metabolism of glucose in the liver. DNA from unrelated individuals was digested with the restriction endonucleases Bgl-I and Taq-I followed by blotting and hybridisation with a 32P-labelled GLUT2 cDNA which revealed three restriction fragment length polymorphisms (RFLPs) (B1, T1 and T2) in both Caucasian and West Indian populations. Linkage analysis between these variant sites demonstrated that the alleles of these polymorphisms were in strong linkage disequilibrium. Disease association of genetic variants at the GLUT2 locus with type 2 diabetes was examined with these RFLPs in both Caucasian (n = 54) and West Indian (n = 46) populations with type 2 diabetes. There were no significant differences in the frequency of alleles, genotypes or haplotypes between diabetic patients and non-diabetic controls. However, there were significant differences in the allele frequencies of all these three polymorphisms between Caucasian and West Indian populations.

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

SummaryThe 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< 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.

The effects of LPS and probucol on interleukin 1 (IL-1) and platelet-derived growth factor (PDGF) gene expression in the human monocytic cell line U-937

We have investigated the effects of lipopolysaccharide (LPS) and probucol (a lipid soluble antioxidant) on the gene expression of interleukin 1 alpha and beta (IL-1 alpha and IL-1 beta), and platelet-derived growth factor A chain and B chain (PDGF-A and PDGF-B) in the human monocytic cell line U-937. Steady-state mRNA levels were measured quantitatively by the reverse transcription-polymerase chain reaction (RT-PCR) using a non-radioactive label. Cells were incubated with LPS, in the presence or absence of probucol for 20 h. The cells were harvested and RNA was then prepared, reverse-transcribed in the presence of an internal standard and subsequently amplified and labelled with digoxigenin-11-dUTP by the PCR reaction. The PCR products were subjected to agarose gel electrophoresis, blotted onto nylon membranes and visualised by immunological detection of digoxigenin followed by a chemiluminescent reaction. We found that: (1) LPS treatment of U-937 cells caused an up-regulation of gene expression of IL-1 beta and PDGF-A chain by approximately 250% and 100% respectively, although it did not stimulate the expression of IL-1 alpha nor PDGF-B chain mRNA. (2) Probucol treatment in vitro had no effect on the basal or LPS-stimulated mRNA levels of IL-1 alpha, IL-1 beta, PDGF-A and PDGF-B despite its reported activity in vivo. (3) PDGF-A and PDGF-B were expressed at a similar level in unstimulated U-937 cells approximately 10-50 copies/ng total RNA, whereas the expression of IL-1 beta mRNA was approximately 2-4 times higher than IL-1 alpha mRNA. (4) Finally, in U-937 monocytic cells the expression of IL-1 alpha and IL-1 beta, and PDGF-A and PDGF-B appear to be independently regulated.

Genetic Variation Around the Collagen IV 1a Gene Locus and Proliferative Retinopathy in Type 2 Diabetes mellitus

The development of proliferative retinopathy in type 2 diabetes mellitus may be under genetic control. A well-documented pathological change in the fundal capillaries of patients with diabetic retinopathy is basement membrane thickening, with an increased amount of collagen IV protein. Variation at the collagen 1a IV gene therefore may explain familial susceptibility to this complication. It has been previously reported that genetic variation at the collagen 1a locus, as shown by allelic association with a HindIII restriction site, predisposes to diabetic nephropathy where basement membrane thickening is also prevalent. In order to test the hypothesis that the collagen 1a IV gene locus is important in the development of diabetic retinopathy, a population association study was performed comparing allele frequencies of the HindIII RFLP in diabetic patients with retinopathy and controls. No statistically significant differences were found between allele frequencies or genotypes in the two groups. The future use of similar studies in diabetic retinopathy is discussed.

Bcl-1 RFLP at the human hepatic lipase gene locus (CIPC)

L.B.Andersen, M.R.Wallace, D.A.Marchuk, R.M.Cawthon, H.M.Odeh, R.Letcher, R.LWhite and F.S.Collins* Departments of Internal Medicine and Human Genetics, and the Howard Hughes Medical Institute, University of Michigan Medical Center, MSRB II, Room 4570, 1150 W. Medical Center Drive, Ann Arbor, Ml 48109-0650, USA and 1 Howard Hughes Medical Institute, University of Utah Medical Center, 603 Wintrobe, Salt Lake City, UT 84132, USA