Association Of Ca～(2+)-independent Phospholipase A₂ Single Nucleotide Polymorphisms With Type 2 Diabetes Mellitus

Diabetes mellitus (DM) is a chronic metabolic disorder which can be divided into two major subclasses: type 1 diabetes mellitus and type 2 diabetes mellitus (T2DM). And T2DM accounts for over 95% of all the diabetes patients. T2DM can be caused by many pathogenies, and it has the features of gradual insulin resistance and relatively insufficient insulin secretion, resulting in hyperglycemia; T2DM is a lifetime disease, can easily supervene some chronic diseases such as heart, blood vessel, kidney, retina and nerve disease. Recent years the incidence of DM has been growing rapidly in China with a current number of diabetes patients over 40 million. DM and its complications not only give the patients distress, but the treantments for them cost a lot also has become a heavy economic burden to our society. So it is urgent to identify the etiology of DM so as to prevent it. Epidemiological study has indicated that T2DM is a disease caused by the interaction between environment and heredity, which belong to polygenic hereditary disease or human complex disease. There are two steps for mapping a disease related gene in the human genome, the linkage-base genome-wide scan and the regional mapping with linkage disequilibrium (LD) analysis. Genome-wide scanning shows that T2DM susceptibility gene regions may be different in different race, having heterogeneity, and there are only 5 chromosome regions which could have a better reproducility. They are 1q, 3q, 8p, 12q and 20q.About 90% variation of the human genome is attributed to single nucleotide polymorphisms (SNPs). SNPs are plentiful, stable and distributing abroad on the chromosome regions, and because SNP can overcome the defectsof restriction fragment length polymorphisms (RFLP) and microsatellite polymorphisms, that are quantity limited, can't reveal situations of the gene and not easy for assessment, it has been more and more used in the studies of inherited diseases, and has been the most important method for human complex disease.This study selected the T2DM patients and heathy control individuals as objectes from Han Chinese in North China. We designed to search for the susceptibility genes for T2DM by screening three single nucleotide polymorphism (SNPs) of GroupⅥphospholipase A2 (PLA2G6) gene in human chromosome 22q13.1 and one SNP of GroupⅣC phospholipase A2 (PLA2G4C) gene in 19q13.3. The polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method was adopted to examine the individual genotypes. Statistical software SPSS 12.0 and Excel 2003 were used to handle the data on genotype. The goodness-of-fitnessχ2 test was used to detect whether the genotype frequency distribution fit the law of Hardy-Weinberg genetic equilibrium. The differences of allelic gene and genotype distribution beween T2DM and control group were detected byχ2 test. Then we determined whether iPLA2 gene was associated with T2DM.The study had detected four SNPs, which as follows: rs2235346, rs2272831, rs2284060 of PLA2G6 gene and rs1549637 of PLA2G4C gene. The sample contents for each case group were 168, 154, 159, 156, and for each control group were 199, 167, 196, 186. All the objectes in both case and control group were aged over 40. The genotype distributions for these four SNPs in case and control group were all in Hardy-Weinberg equilibrium by goodness-of-fitnessχ2 test. The genotype frequency distributions (GG:GT:TT) for PLA2G6 rs2235346 locus were case group 46:73:49, and control group 47:89:63. For rs2272831 locus (GG:AG:AA) were 97:51:6 and 113:44:10. For rs2284060 locus (CC:CT:TT) were 10:64:85 and 10:81:105. Andthe frequency distributions of the allelic gene and genotype for the three SNPs were found no significant differences between the T2DM group and control group. The genotype frequency distributions (AA:AT:TT) for PLA2G4C rs1549637 locus were case group 117:35:4, and control group 134:47:5. And the frequency distributions of the allelic gene and genotype for the SNP were also found no significant differences between the T2DM group and control group.All the above suggested that the three SNPs of PLA2G6 gene and one SNP of PLA2G4C gene may have no association with T2DM. The results of the study point out that the single nucleotide polymorphisms of iPLA2 gene may have no association with T2DM in Chinese northern Han people. Although the result is negative, we can't eliminate the association of other SNPs of iPLA2 gene and other PLA2 genes with T2DM. In order to investgate the association of PLA2 gene single nucleotide polymorphisms with T2DM, we should increase the sample content, screen more SNPs, and approve the association in different districts and different races.