Clinical characteristics of participants
There were 950 CAD subjects (mean age of 58.68±7.30 and 47.14% of men) and 1082 controls (mean age of 58.68±7.29 and 46.43% of men) that were involved in the analysis. As Table 1 shown, comparing the control groups, the clinical characteristics of CAD patients at baseline showed lower HDL, and higher body mass index (BMI), glucose, blood pressure, uric acid, TG, and prevalence of smoking, hypertension, alcohol intake, and diabetes (all p<0.05). However, the parameters of age, gender, LDL-C, and TC have not shown any differences between the groups.
Distribution of genotypes in the polymorphisms of the PCSK9 gene between the CAD and control groups.
Four SNPs of PCSK9 (rs11583680 C>T, rs2483205 C>T, rs2495477 A>G and rs562556 G>A) were genotyped in both CAD and control groups. As Table 2 exhibited, the distribution of each genotype, genetic models, and alleles of the four SNPs was separately examined in CAD patients and controls. Except for the rs2495477 in the CAD group, all the genotype frequencies in both groups were in HWE (p > 0.05). For the rs2483205, the distributions in CC, CT, and TT genotypes, and in its recessive model(TT vs. CC+CT)were different between the two groups (p = 0.025, and p = 0.008, respectively). For the rs562556 , the distributions in AA, AG, and GG genotype, A and G alleles, and its dominant model (AA vs. GG+AG)were also significantly different between the two groups (p = 0.020, p = 0.005 and p = 0.006, respectively). However, comparing the control group, the distributions of genotypes, models, or alleles of rs11583680 and rs2495477 have not shown any significant differences in the CAD and control groups (p = 0.294, and p = 0.342, respectively).
Independent risk factors for CAD
To determine whether the polymorphisms of the PCSK9 gene were the independent risk factors for CAD, we adjusted confounding risk factors, including BMI, TG, TC, HDL-C, and LDL-C, the prevalence of hypertension, diabetes, smoking, and drinking. We found that the recessive model (CC vs. TT+CT) of rs2483205 and the dominant model (AA vs. GG+AG) of rs562556 were still showed a significant association with CAD. The TT genotype of rs2483205 was indicated the protective effects on CAD (OR = 0.53, 95%CI = 0.29-0.95, p = 0.032) (Table 3), and the GG genotype of rs562556 was also exhibited a benefit effect (OR = 0.57, 95%CI = 0.34-0.95, p = 0.032) (Table 4).
LD analysis
Table 5 is displayed the patterns of LD analysis in the PCSK9 gene. We have identified that these four SNPs are located in the same haplotype block. Except for rs2483205 (SNP2) and rs2495477 (SNP3), all the r2 values of SNPs were below 0.5, which means that we could not construct haplotypes by SNP2 and SNP3 simultaneously. In addition, because the minor allele frequency (MAF) of SNP2 is larger than SNP3, we just used SNP1, SNP2, and SNP4 to construct the haplotypes. In further, because the |D’| for rs11583680 (SNP1)-SNP2, SNP1–SNP3, and SNP1–(rs562556) SNP4 were <0.5. So we do not use the SNP1 to construct haplotypes. At last, the SNP2 and SNP4 were used to construct haplotypes.
Relationship between the haplotypes of the PCSK9 gene and CAD
As Table 6 is shown, we established the haplotypes by combining the SNP2 and SNP4. Then, the distribution of the SNP2–SNP4 constructed haplotypes between the two groups was analyzed. The haplotype distributions of C–G (H2) and T-G (H4) were significantly different between the two groups (p<0.05). The frequencies of H2 haplotype were significantly higher in the CAD group than in the control group (OR = 1.97, 95%CI: 1.013-3.842, p = 0.042). However, compared with the healthy control subjects, the frequencies of H4 haplotype were significantly lower in patients with CAD (OR = 0.495, 95%CI: 0.351-0.699, p < 0.001).
The relationship between PSCK9 genotypes and lipids levels
The relationship between the genotypes of polymorphisms and lipids levels was analyzed. Individuals with TT genotype in rs2483205 had significantly lower mean TC level than CT genotype (4.62±2.62mmol/L vs. 3.91±1.20 mmol/L, p = 0.025), Figure 1a. And there is lower mean LDL-C level in G allele than A allele in the rs562556 (2.71±0.99mmol/L vs. 2.41±0.97mmol/L, p = 0.048), Figure 1b. Nevertheless, neither HDL-C nor TG showed any significant difference among different genotypes of rs562556 or rs2483205 (p > 0.05).