| Alzheimer's disease (AD) is a genetically heterogeneous disorder. Mutations in the genes encoding the amyloid precursor protein, presenilin-1 and presenilin-2 may cause relatively rare early-onset familial AD. In contrast, for the more common sporadic AD, apolipoprotein E (APOE) 4 allele is the only widely confirmed genetic risk factor. However 40-60% patients with sporadic AD do not carry any APOE e4 allele, suggesting the presence of other genetic risk factors.There are numerous reports of genetic association findings in sporadic AD. The dominant approach to the association has been to study the polymorphisms within the candidate genes from biological pathways and processes strongly implicated in the pathogenesis of AD. The proteins coded by such genes are principally involved in amyloid peptide (AP) metabolism, oxidative stress, apoptosis/inflammation and vascular disease. Among the reported associated genes, amyloid precursor protein P-site cleaving enzyme (BACE1), alpha-2 macroglobulin (A2M), apolipoprotein Cl (APOC1) and neprilysin (NEP) may involve in A metabolism, while paraoxonase 1 (PON1) and PON2 act as antioxidant antioxidants. However, results of association analyses with polymorphisms in aforementioned genes are still contradictory, and little is known about the status in Chinese.In the present study, the association analyses between the known SNPsof the 5 genes mentioned above and sporadic AD were performed and a whole-gene screening for possible novel SNPs in NEP gene was conducted in a Chinese population including 257 AD patients and 242 controls using polymerase chain reaction, restriction fragment length polymorphism, denaturing high performance liquid chromatography, molecular cloning and DNA sequencing techniques. The results were as follows:1. The frequency of ApoE s4 allele increased significantly in moderate to severe dementia subgroup (19.8% vs. 8.1%, x2= 20.30, P < 0.001) while was similar to that in mild dementia subgroup (8.6% vs. 8.1%, x2= 006, P > 0.05).2. The frequencies of 1239C allele and CC genotype in the BACE1 gene were found to be significantly higher in mild AD patients (by allele x2=5.71, P < 0.05; by genotype x2=6.71, P < 0.05), but not in moderate to severe dementia subgroup (P > 0.05) as compared with those of controls.3. No significant difference of allelic or genotypic frequencies either of I1000V polymorphism in A2M gene or of Q192R polymorphism in PON1 gene between the patients and control subjects were observed.4. The 311C allele frequency in PON2 gene was significantly higher in the patients with moderate to severe dementia (x2=4.16, P < 0.05), but not in those mild dementias.5. The A allele as well as AA genotype frequency in the APOC1 gene was found to be significantly higher in moderate to severe AD patients (by allele x2= 7.29, P < 0.01; by genotype Fish's exact test, P < 0.01), but not in mild patient subgroup.6. When all subjects were divided on the basis of the APOE 4 status,the 1239 CC genotype frequency in the BACEl gene remained significantly higher in mild non-APOE 4 arring AD patients (x2=3.96, P < 0.05), andc the AA genotype frequency in the APOCl gene was still significantly higher in moderate to severe patients carring 4 (P < 0.05). While the APOE 4 status did not influence the polymorphic distribution of other candidate genes.7. Pairwise linkage disequilibrium analyses showed that the polymorphic loci between APOE and APOCl were in strong linkage disequilibrium (D' = 0.5491, P = 0.0000), and that PON1 Q192R and PON2 C311S polymorphisms were in weak linkage disequilibrium (D'=0.1867, P =0.0339).8. Haplotype analyses with EH program demonstrated that the frequency of APOE e 4/APOC1A haplotype in moderate to severe AD patients was significantly hingher than that of controls (P < 0.01).9. Screening of the NEP genetic polymorphisms realed 11 SNPs, of which 9 were novel, namely, +4226G/A, +5284T/G, +60517C/T, +64932T/A, +80427C/T and +92579C/A were in intron 2,3,10,15,17 and 22, repectively, -204G/...
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