Genomewide scan for quantitative trait loci of angiotensin converting nzyme activity and finemapping of its structure gene

• Main Authors: Ruey-Yun Wang, 王瑞筠
• Other Authors: Wen-Harn Pan
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/89049178160334194800

博士 === 國防醫學院 === 生命科學研究所 === 95 === Genetic variation in angiotensin converting enzyme (ACE) has been associated with hypertension and cardiovascular diseases. ACE plays major roles in the pathogenesis of cardiovascular diseases in previous studies. However, the findings on the association between ACE insertion/deletion polymorphism in intron 16 and hypertension/cardiovascular diseases are not consistent. Up to now, it’s still unclear whether the I/D polymorphism is a functional variant for ACE activity on chromosome 17. Regulation of ACE expression may be more complex than our expectation. The purpose of this study was using genowide scan linkage analysis to map the quantitative trait loci (QTL) for serum ACE activity and finemapping. We recruited 1271 individuals from 373 young-onset (onset age ≤ 40 years) hypertension pedigrees. The set of 479 microsatellite markers of deCODE genetics were used. The mean heterozygosity was 0.75 and the markers provide a ~10 cM resolution and average in human index map was typed for the study subjects. The microsatellite markers were performed linkage analysis with genomewide scan for ACE activity. The estimated heritability of ACE activity trait was 0.58 after controlling for gender and two major medications (β- adrenergic blocking agents and ACE inhibitors). MERLIN software was used for genomewide scan linkage analysis. We identified a strong linkage peak near the ACE structure locus on chromosome 17 at 89.6 cM (LOD=4.60). We further identified a previously unfound loci on chromosome 9 at 149.4 cM (LOD=3.00) as well. Subsequently, we genotyped 41 single nucleotide polymorphisms (SNPs) selected 12 genes (including ACE locus) in the strongest peak of chromosome 17 to narrow down the potential regions. Only one SNP within ACE was significantly associated with what in the family-based association test (FBAT). Therefore, we focus to finemap the ACE locus. 31 SNPs within and around the ACE gene were genotyped. TRANSMIT programs were performed to relate two ACE activity levels (80th percentile cut-point) with individual SNP for transmission disequilibrium test. The region most significantly associated with two ACE activity levels was between intron 20 and exon 24. In addition, four linkage disequilibrium (LD) blocks and 5 tagSNPs were revealed from 31 SNPs. TagSNP rs1800764 on LD block 2, upstream from and near the ACE promoter, was significantly associated with young-onset hypertension (-log10(p)=1.45) by GEE (generalized estimating equation) model adjusted for age, gender, and drugs, and controlled for intra-family correlation. Five tagSNPs on four LD blocks were significantly associated with quantitative ACE activity (p-value: 10-4 to <10-30). We constructed two major haplotypes, TTGCG and CCATA (allele frequency was 62 % vs 28 %, respectively) with 5 tagSNPs. The highest mean ACE activity was 18.91 IU/l observed for CCATA with homozygote, and the lowest mean ACE activity was 11.69 IU/l for TTGCG homozygote, with the mean ACE activity of TTGCG/CCATA heterozygote, 15.58 IU/l, in between. The mean ACE activities were the significantly different (p<0.0001) between these two homozygotes. This study have not only identifitied a previous unknown locus on chromosome 9 at 149.4 cM (LOD score 3.0), but also revealed that the strongest QTL influencing ACE activity was in the ACE gene on chromosome 17. The regulation mechanism of ACE activity may be more complex. The variants in ACE gene which might effect the variation of ACE activity will perform as functional assay.