Study On The Association Of Apolipoprotein A5 Gene Single Nucleotide Polymorphisms With Type Ⅱ Diabetes

Diabetes is a complex disorder caused by multiple genetic and environmentalfactors. Type II diabetes mellitus (non-insulin-independent diabetes mellitus,NIDDM) occupied about 90 percent of all diabetic patients. Some risk factors,such as diet, heredity, age and obesity likely contributed to the generation anddevelopment of diabetes mellitus. The genetic factor is generally considered asone of risk factors of NIDDM, and the hypertriglyceridaemia is also theprominent feature of the dyslipidemia commonly observed in NIDDM, as anindependent risk factor of the coronary artery diseases (CAD) complications ofNIDDM.Apolipoprotein A5 gene (APOA5) identified newly is a fourth member of thechromosome 11 apolipoprotein gene cluster with apolipoprotein A1/C3/A4together. The previous researches on APOA5 indicate that APOA5 is animportant determinant of plasma tyiglyceride levels in human and mice. Themodels of transgenetic mice overexpressing human APOA5 and knock-out micelacking Apoa5 observed that the triglyceride levels of the former were aboutone-third of these of control group, but the latter were about four times as muchplasma triglyceride as their controls. Meanwhile, the function influencingtriglyceride levels is independent on others apolipoprotein genes in this cluster.Therefore, APOA5 gene is an important gene regulating plasma triglyceridelevels. In post-genomic era, studies on association of sequence variation withphenotype are the main subject of medical genetics. Single nucleotidepolymorphisms (SNPs), the third-generation genetic marker, possess thecharacteristic of large numbers and dispersed distribution. As SNPs is bi-allelicpolymorphism, it is impossible to detect easily and analyze with largely scale.Association study based on population level may find the possible SNP and/orhaplotype associated with the complex and multiple genestic disease. They are ofimportance for clarifying the genetic pathology of some polygenetic inheritancedisease. To investigate the impossible association and roles of APOA5 gene indyslipidaemia and NIDDM, firstly, we examined the distribution of 3 knownSNPs (1131T>C, APOA4/A5 and S19W) of APOA5 gene and 1 known SNP(SstI) of APOC3 gene in 214 Chinese patients with NIDDM and 472 controls byPCR-RFLP. Secondly, we screened primarily the unknown SNPs of the APOA5gene by high-throughput denaturing high-performance liquid chromatography(DHPLC). Finally, we analysed the association of these SNPs with lipidmetabolism in patients with NIDDM. As to 4 known SNPs, there was no significant difference in distribution ofgenotype and allele frequencies of –1131T>C polymorphism in APOA5 genebetween NIDDM and control groups. The frequencies of T and C allele wererespectively 64.72%, 35.28% and 68.43%, 31.57% in NIDDM and controlgroups. The triglyceride levels of patients with CC genotype were highersignificantly than those with TT (P=0.004) in NIDDM, and in control group, thetriglyceride levels of individuals with TC increased significantly, compared withthose with TT (P=0.001). The distributions of APOA4/A5 polymorphism weredifferent significantly in Chinese and Western population. The T allele, as wildallele in western population, on the contrary, is minor allele in Chinesepopulation. In NIDDM and control groups, the frequencies of C and T allelewere 58.02%, 41.98% and 63.14%, 36.86%, respectively. There was no differentin two groups (P>0.05). However, the triglyceride and total-cholesterol levels ofpatients with TT allele were higher significantly than those with TC or CC inNIDDM, but there was no difference on lipid levels of three genotypes in controlgroup. The distributions of SstI polymorphism in APOC3 gene were no differentsignificantly in NIDDM and control groups (P>0.05), and the allele frequenciesrespectively 69.31%, 30.69% and 71.38%, 28.62%. However, in NIDDMpatients, there was significantly difference in the distribution of genotype andallele frequencies in subgroups of NTG and HTG (χ2=20.21, P=0.0000; χ2=19.86,P=0.0000). In NIDDM and controls groups, S2S2 genotype individuals exhibiteda significant increase in plasma TG concentrations, respectively compared withS1S1 and S1S2 individuals of each group (P<0.01). As to S19W polymorphism,we have not observed in our research population. In addition, we observed a suspect novel mutation (+541G>T) in exon3 ofAPOA5 gene. The suspect heterozygoties found by DHPLC will be examined bysequencing and PCR-RFLP.