| Objective Mitochondron. is the special organ which stores and supplies energy for cells, mitochondrial DNA (mtDNA) is the only extra-chromosomal genome in human cells, which can replicate, transcript and encode autonomously. It encodes for 13 kinds of essential proteins of the respiratory chain, which are needed for the oxidative phosphorylation (OXPHOS). Since mitochondrial OXPHOS plays an important role in the glucose-induced insulin secretion in pancreatic beta cells, the relationship between mitochondrial gene defect and the development of diabetes mellitus (DM) has been widely attended. In 1997, American diabetes association (ADA) put this type of DM into the subgroup of special diabetes mellitus, which has genetic defects in pancreatic beta cells. In the study, 300 randomly selected, unrelated patients with type 2 DM and 280 normal controls were included. 4 positions in mtDNA1^" (UUR) gene and its adjacent region were screened, which were thought to be genetic hot spots for DM. The aim of this study is to investigate the prevalence of mtDNA gene mutations and find out the relation between mtDNA mutations and microvascular complications. Moreover a simple and sensitive way to be performed in clinical diagnosis of DM caused by mitochondrial gene mutation may be developed.Methods1. Collecting the blood samples according to ADA criteria of type 2 DM.2. Extracting and purifying the genomic DNA from the blood samples.3. Using PCR-RFLP analysis, 4 mtDNA positions (np3243, np3316, np3394, np3426) were screened in 300 type 2 diabetics and 280 normal controls.4. Sequencing the mutation genes screened by RFLP.5. Analysize the clinical data.Results In the study, 8 (2.69%) with the mutation of np3316G- A, 12 (4.00%) with np3394T-C, and 2 (0.67%) with np3426A- G were found in type 2 DM group. In controls, 2 (0.71%) with that of np3394 were secreened. However the well-known mutation of np3243 was not found. The mutations of np3316G- A and np3394T-C had significiant differences between two groups (P<0.05, respectively), and that of np3426A- G was on the contrary. The mutation group showed obvious family history of DM (P<0.05) and tendency of maternal inherition (P<0.01). The age when DM came on was correlative with mtDNA mutations (P<0.05). However, there was no relationship between the microvascular complications and mtDNA mutations (P<0.05).Conclusions The mutations at np3316, np3394 and np3246 are all located in the mtDNA NADH dehydrogenase subunit 1 (ND1) region. It is well known that the np3316 G- A changes a nonpolar alanine to a polar threonine (GCC- ACC), the np3394T-C turns a conserved tyrosine to histidine (TAT -CAT) and np3426A-G is not a missense mutation (GTA- GTG). These point mutations may involve in the development of type 2 DM by decreasing the activity of ND1 . The famous mutation of mtDNA np3243 A-G which can lead to abnormality of tRNALcu(UUR)gene is proven to be the reason of maternally inherited diabetes and deafness (MIDD). However, it was not found in the study. It indicates that the point mutations at np3316, np3394 and np3426 of ND1 may contribute to the occurrence of type 2 DM. |
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