In this study we investigated the associations between SNPs of lipid metabolizing genes and their relations to 493 diagnosed CHD cases and 412 healthy controls from Han Chinese population in Xinjiang region of China. We chose four different SNPs related with lipid metabolism, they are rs1122608 in SMARCA4,rs2230806 in ABCA1, rs12563308 in ANGPTL3, and rs662799 APOA5 and evaluated whether they were associated with lipid levels and the risk of CHD in Han Chinese population. Our results showed no significant differences of these SNPs and their genotypic and allelic distributions between control and CHD group(P > 0.05)(Table 2). In other words there is no statistically significant association between above four SNPs and CHD risk. Serum level of HDL-C was higher in TT genotype of rs1122608 when compared with GT and GG genotype (P < 0.01); serum Triglyceride(TG) levels was higher in rs662799 GG genotype than GA and AA genotype(P < 0.00); AA of rs662799 had higher HDL-C level compared with the other two genotypes (P < 0.01) ; rs12563308 and rs223086 were not associated with any serum lipid traits (P > 0.05 for all) (Table 4). Following multivariate adjustments for the confounders, such as age, sex,smoking,hypertension and diabetes, rs1122608,rs2230806, rs12563308,and rs662799 were still not related with CHD (P > 0.05 ). Also no association was found between four SNPs with gensini score and the angiographic severity of CHD patients (P > 0.05 )(Table 5).
Genome-wide association studies have identified rs1122608 SNP, located in intron 30 of BRG1/SMARCA4, as a risk variant for CHD [25]. Moreover, much evidence has verified that rs1122608 is related to CHD independently of lipid profiles [26,27]. A report of this SNP on Iranian populations showed that intron 30 of SMARCA4 gene include rs1122608 was associated with a strong protective effect against CHD[28]. Fujimaki et al.[29] performed a case-control study and that rs1122608 of SMARCA4 (P < 0.0305; dominant model; odds ratio, 0.86) is a risk factor of hypertension in Japanese individuals. Guo X, Wang X, et al[30] found significant differences in glucose concentrations of rs1122608 different genotype, but no significant association was found between rs1122608 polymorphism and Coronary heart disease or lipid metabolism in Han population living in Xi’an city. In a different Chinese Han study population, it has been pointed out by Chen QF, et al[31] that the mutant GT and TT genotypes and minor T allele of rs1122608 are positively correlated with the risk of AMI. Another study showed, rs1122608 was associated with a higher risk of revascularization of cardiovascular complications in patients with CAD confirmed by coronary angiography[32] .Meta-analyses performed for rs11206510 and rs1122608 showed that two SNPs were associated with CHD in Caucasians but not in Asians[33]. Ma H[34] also found rs1122608 in SMARCA4 seemed to have a strong protective effects on the hypertension. Above results showed the controversy effect of this SNF on lipids and CHD.
Our study showed TT genotype of rs1122608 was associated with higher HDL-C levels, therefore may act as a protective factor, however this theory should be proven further due to biographical and ethical backgrounds of our samples(Table 4).
Angiopoietin like 3 gene (ANGPTL3) encodes a member of a family of secret proteins that function in angiogenesis which is involved in the metabolic regulation of triglycerides, LDL-C, and HDL-C, as well as atherosclerosis in mice and humans [35]. Previous GWASes also reported that some ANGPTL3 polymorphisms were associated with serum TG and TC levels[36]. rs12563308 SNP belongs to ANGPTL3 gene family, but little is known about the association of the ANGPTL3 rs12563308 single nucleotide polymorphisms (SNPs) with serum lipid levels and the risk of CHD. Li[37] showed that ANGPTL3 rs12563308 SNPs were not associated with all of seven serum lipid traits in the controls,but rs12563308T haplotype was associated with an increased angiographic severity to coronary artery atherosclerosis. Gong Q el at[38] explored associations between genetic variants of the ANGPTL3 gene and susceptibility to ischemic stroke in a large-scale case–control study in a Chinese population. They found that rs12563308 were significantly associated with susceptibility to ischemic stroke. They also pointed out that carriers of the minor allele of SNP rs12563308 had significantly lower levels of TC and LDL-C. A study in a Finish population showed that subjects who carried ANGPTL3 sequence variants rs12563308 (n = 4) and rs199772471 (n = 1) had abnormally high TC and LDL-C concentrations[39].
In our study, rs12563308 was not associated with any serum lipid traits (P > 0.05 for all). Also no association was found between rs12563308 with gensini score and the angiographic severity of CHD patients (P > 0.05 )(Tables 6 and 7). However, the reason for these discrepancies in different investigations is still unclear.
The SNP rs2230806 is located in ATP-binding cassette transporter A1 (ABCA1) gene. ABCA1 is a membrane transporter protein that plays an essential role in the effelux of cholesterol from peripheral tissues back to the liver, thus has a crucial role in removing intracellular cholesterol and plays a protective role against atherosclerosis[40]. In recent years, a number of studies have shown that the distribution frequency of specific ABCA1 gene SNPs in different regions and populations is significantly different, therefore the effects on plasma lipid levels and the incidence and severity of CHD are also different[41]. Even the same ABCA1 gene SNPs have similar or opposite effects [42,43]. Therefore, genetic polymorphisms in this gene may alter the susceptibility or the improvement of CHD. Fan Q el at[44] showed in a meta Analysis of a total of 34,348 subjects (14,085 CAD cases and 20,263 healthy controls) that there is a significant association between rs2230806 polymorphism and the risk of CAD under different genetic models: an allelic genetic model (OR = 0.745, 95% CI = 0.687–0.809, P < .001), a recessive genetic model (OR = 0.683, 95% CI = 0.603–0.774, P < .001), a dominant genetic model (OR = 0.703, 95% CI = 0.633–0.781, P < .001), a homozygote genetic model (OR = 0.573, 95% CI = 0.488–0.672, P < .001), and a heterozygote genetic model (OR = 0.761, 95% CI = 0.693–0.837, P < .001), In addition, statistical result showed rs2230806 is significantly associated with CAD in Asian population, marginally significant in Caucasian and not significant in other group. The reason for racial difference phenomenon may be attributed to allele frequency and other factors, such as lifestyle discrepancy and so on. Ma et al[45] indicated rs2230806 is a protective factor for CAD risk both in Asians (OR = 0.76, 95% CI = 0.68–0.85) and Caucasians (OR = 0.89, 95% CI = 0.81–0.99. Wang F el at[46] study results showed that AA genotype of the rs2230806 polymorphism had higher levels of TC, LDL-C and uric acid than those with GA genotype (p < 0.05 for all) but no associations between rs2230806 polymorphism and severity of CAD was detected.
Our results also found no association between rs2230806 genotype and severity of CHD or with serum lipids levels(Table 4,6,7).
Apo-lipoprotein A5 (ApoA5) is part of VLDL, HDL and CM and is a major regulator of blood TG and HDL-C through interaction with LDLR[47]. Rs662799 was a polymorphism located in APOA5 gene and is the most studied SNP in the promoter region of this gene [48]. The allele frequency of rs662799 in HapMap database was 1.7, 13.3. 26.7 and 28.9% in European, African, Chinese and Japanese respectively. Chen H et al[49] found a significant association of the SNP rs662799 in APOA5 genes with CAD. Valente-Frossard TNS[50] showed in their study that genotypes of the APOA5 rs662799 were not associated with lipid levels. Another study of Korean metabolic syndrome subjects showed that SNP rs662799 in the APOA5 gene was associated with increased risk of metabolic syndrome and its components, especially elevated TG and low levels of HDL-C [51]. Hsu LC [52] also found out TC + CC genotype of rs662799 is associated with high serum triglyceride and low LDL and BMI levels in the Han Chinese population in Taiwan.
In our study we also found ApoA5 rs662799 was associated with elevated TG in Han Chinese subjects in Xinjiang. The same results was reported in a study conducted in India where the rs662799 was associated with 19% increase in serum TG levels[53], similar TG raising effect of this SNP has also been reported in Chinese people other than Xinjiang region and Paksitani subjects[54,55]. Therefore, ApoA5 rs662799 might play in TG metabolism in Han Chinese people in Xinjiang.
To sum up, in our study, we confirmed polymorphisms of rs1122608(SMARCA4), rs2230806(ABCA1), rs12563308 (ANGPTL3) and rs662799( APOA5) are not different between CHD patients and normal control subjects in Xinjiang Han Chinese population, suggesting that these SNPs and their genotypes and alleles may not be associated with CHD in Han Chinese population in Xinjiang. Among these SNPs rs1122608(SMARCA4) TT allele and rs662799( APOA5) AA allele were associated with elevated HDL-C levels meanwhile rs662799( APOA5) GG alelle was also associated with elevated TG levels. According to our results we also concluded these SNPs have no affect on the severity of CHD. GG genotype in rs662799 might be related to the elevated TG levels in CHD patients, therefore may act as a risk factor for CHD, TT genotype of rs1122608 and AA genotype of rs662799 are related with higher HDL-C levels, therefore may play a protective role in the development of CHD in Han Chinese population in Xinjiang region
Investigating these SNPs should use more clinical data with bigger samples. Our current research is fundamental; further functional studies and larger population-based prospective studies are required to understand the genetic factors underlying CHD.