Statins are the first-line drugs for both primary and secondary CVD prevention in HPL patients [20]. Numerous clinical studies have demonstrated that statin drugs are effective against CVD [3], and their efficacy may be modified by a variety of factors including genetic polymorphisms [21]. The current study expands on previous pharmacogenetic studies of statin efficacy in other populations, and we seek to learn more about how particular genetic polymorphisms, together with other patient or clinical factors, predict statin-related lipid profile changes in a subset of Malaysians with HPL. Indeed, by comparing two geographically distinct populations, such as Malaysian (a proxy for East Asians) and British (a proxy for Europeans), pharmacogenetic data can be utilized to predict different clinical outcomes of pharmacological therapy [22]. The findings in this study highlight a clear association between certain SNPs (e.g., ABCG2 rs2231142, APOA5 rs662799, and ABCC2 rs717620) and lipid profiles of HDL-c or LDL-c in Malays prior to statin treatment, suggesting a different lipid metabolism status among the patients thus the SNPs may exhibit protective effects or risk factors for CVD. Following statin treatment with low and moderate intensity statin doses (10–40 mg/day). Possession of at least one minor allele of the SNPs, i.e. ABCC2 rs717620 and APOA5 rs662799, significantly improved statin-related lipid profile changes, particularly HLD-c and TG, but not LDL-c levels. Statins, but not any variants in genes studied, were significantly beneficial in lowering LDL-c levels (P < 0.001), implying that the LDL-c lowering effects of statins were exclusively pharmacological.

Only two of the seven SNPs investigated, i.e. ABCC2 rs717620 (C > T) and APOA5 rs662799 (A > G), were associated with different lipid profiles in HPL patients both before and after statin treatment. Following longer statin treatment (within 7 to 12 months duration), both SNPs associated with improved TG profile; reduced TG levels were found in minor allele carriers of the SNPs (Table 4). Minor allele T carriers of ABCC2 rs717620 were shown to have a lower TG/HDL index ratio (P = 0.030) in Chilean population (n = 127) treated with a low-dose atorvastatin (10 mg/day) [23], indicating a greater efficacy of atorvastatin-related TG-lowering effects with the SNP. The ABCC2 gene, which encodes the multidrug resistance-associated protein 2 (MRP2) membrane efflux transporter, is necessary for cellular efflux of its substrates, including statin, and controlling its hepatobiliary excretion [24]. The ABCC2 rs717620 variants have been associated with decreased MRP2 expression and function, resulting in higher bioavailability and thus improved the efficacy of atorvastatin and other statins [24, 25]. In this study, minor allele T carriers of the ABCC2 rs717620 SNP also had higher TC (P = 0.040) and LDL-c (P = 0.022) levels at the baseline prior to statin treatment (Table 4), suggesting an increased CVD risk among the SNP variants, and the risk was encountered with significant TC- and LDL-lowering effect with statin treatment. Since our analysis was not corrected by means of body mass index (BMI), one of the most prominent confounding factors in lipid levels [26], we were unable to determine whether the minor allele T carriers had high BMI values, which reflected their high TC and LDL-c levels. However, stratification based on individual genotypes and patient gender in the analysis would eliminate the confounding effects. A large cross-sectional study from the USA (n = 12,383) and Spain (n = 11,765) found that LDL-c levels increased significantly (P < 0.001) by 23.0 mg/dL and 24.1 mg/dL, respectively, per kg/m2 increase in BMI, though the effect was only observed below the BMI inflection points (27.1 kg/m2 and 26.5 kg/m2, respectively) [27]. Similarly, an obese group (BMI ≥ 25 kg/m2) had higher (P < 0.01) LDL-c than the lean group (BMI < 25 kg/m2) in a non-diabetic Chinese population (n = 1538) [28], further suggesting the impact of BMI on LCL-c levels.

In terms of TG profiles, we found an association between APOA5 rs662799 (A > G) and lower TG levels, which were predominantly observed in male patients carrying minor allele G (Fig. 1) suggesting a higher TG metabolism among the minor allele carriers of the SNP. The TG-lowering effects were most likely related to the atorvastatin treatment, regardless of the specified dose (data not shown). The APOA5 gene was identified as a key regulator of plasma TG levels [11]. Despite the fact that most evidence from both animal and human studies indicated that APOA5 rs662799 (found to result in a 50% decrease in the APOA5 gene expression) was associated with higher plasma TG levels [29], minimal inter-ethnic heterogeneity were discovered [30]. A study in Hong Kong (n = 1375) and Guangzhou (n = 1996) populations also found that GG genotypes had 36.1% (P = 2.6 × 10–13) and 30.0% (P = 1.3 × 10–12) higher plasma TG levels, respectively, than homozygous dominant AA genotypes [31], while another Chinese ethnic (Han) population (n = 200) found that GG genotypes were significantly associated with reduced TG levels (P = 0.047), compared with other genotypes, in just three months of atorvastatin (20 mg/day) treatment [32]. Similar findings supporting the former observations were observed in other populations including Pakistani (n = 712) and North Iranian (n = 199) [33, 34]. Our study found no association between APOA5 rs662799 and the statin-related LDL-lowering levels in patients. However, minor allele G carriers of the SNP resulted in a significant LDL-c reduction (P < 0.005) following three months of low dose statin, regardless of the type of statin, in Caucasians (n = 154) [35]. Considering APOA5 rs662799 had a strong association with higher HDL-c levels (Table 4 and Fig. 1) at baseline (P = 0.007) and during statin treatment (P = 0.031), we assumed that this SNP may have a protective effects against CVD risk, as previously demonstrated [36,37,38]. Our findings supported those of the Turkish Cypriot population (n = 100), which indicated that GG genotypes had considerably higher HDL-c levels (P = 0.014) than other genotypes [39].

Gender and, to a lesser extent, ethnicity are the key factors affecting inter-individual variability in lipid levels such as TG and HDL-c [40]. Thus, it is critical to corroborate our findings on the impact of gender on the lipid profiles. It is worth noting that APOA5 rs662799 and ABCC2 rs717620 had gender-specific effects on lipid profiles, thus corresponded with our previous findings with the CETP gene [19]. Before statin treatment, males carrying the minor allele G for APOA5 rs662799 had higher HDL-c levels (P = 0.007) than the wild-type AA genotypes, and HDL-c levels remained significantly higher (P = 0.031) during statin treatment. Also, during statin treatment, TG levels were significantly lower in the APOA5 rs662799 variants but not in the wild-type AA genotypes (Fig. 1a), suggesting that the SNP has a protective effect against CVD risk. The gender-specific effect on TG levels in males in our study, to some extent, explained previous findings in humans and mice [41]. In a large longitudinal study (n = 4329), AA genotypes of the SNP had a higher incidence of dyslipidemia (OR 1.50, 95%CI, P < 0.001) than their AG and GG counterparts [42]. In contrast, prior to statin treatment, the ABCC2 rs717620 variants may have a higher CVD risk, probably due to increased TC and LDL-c levels. The lipid profiles during statin treatment were determined by the pharmacological effect of the drug since the significant statin-related lipid-lowering effects were unaltered with different genotypes (Table 4). Above all, the specific type of statin, i.e. pravastatin, determined the patient’s attainment of the LDL-target of 2.6 mmol/L (Table 5), rather than the effect of other variables such as SNPs or patient’s demographic profiles.

In addition to female gender [43], there is consistent evidence that advanced age and low body mass contribute to statin adverse effects [44, 45]. In this study, gender and age factors did not independently predict patient’s attainment of the LDL-target of 2.6 mmol/L (Table 5). The mean age of patients in this cohort (53 ± 7.16 years old) was not different between males and females, as reported previously [19]. In terms of statin efficacy, there is conflicting evidence among older people (generally defined as more than 65 years old); a meta-analysis of 28 randomized controlled trials found that statin therapy, regardless of patient age, resulted in significant reductions in major vascular events [46], implying a minimal effect of patient age on statin efficacy, but this was not evident for statin-related adverse effects [44]. However, the temporal relation between the study outcomes and the above-mentioned patient factors may be easier to be interpreted in a prospective design, rather than this cross-sectional retrospective approach.

Our study has a few limitations. First, the current study examined the effect of a single SNP on lipid-lowering effects of statins without taking gene–gene interaction into account. The possibility of gene–gene interactions has been demonstrated in relation to statin efficacy and toxicity. Females with the APOE E4 variant allele, for example, reduced the effect of APOA5 rs662799 on TG levels in Caucasian (n = 2500), suggesting a sex-specific interaction between the two genes [47]. Similarly, the inclusion of an important genetic predictor in determining statin efficacy, such as solute carrier organic anion transporter family member 1B1 (SLCO1B1), the most relevant gene underlying statin-related side effects from a genome-wide association study [48], is necessary. In fact, the gene has been replicated in many gene association studies. The SLCO1B1 polymorphism, along with the gender factor, was found to be the only significant gene candidate predicting statin-related muscle toxicity [49]. Next, our findings were most likely restricted to the effect of low and moderate intensity statin doses (approximately 86% of the included patients were on 10 to 20 mg/day) on the lipid profile for all types of statins. Although we were unable to directly determine which statin has the optimum effect on lipid profile, our findings did, in part, explain genetic involvement in lipid profiles changes before and after statin treatment in general. In order to prescribe personalized medicine among statin users, future studies should focus on individual statins because their effect on lipid profile varies, and the consideration of pharmacogenetic-related gender involvement in patient management is necessary. For example, rosuvastatin resulted in significantly higher LDL-c reductions across dose range compared to other statins [50]. Our study also lacked sufficient study power to assess the impact of each type of statin on the measured lipid profiles because of the unequal number of patients among different statin users. Furthermore, the different properties of statins (hydrophilic versus lipophilic statins) were more relevant in explaining statin-related adverse effects [44]. In this study, we also included the two cases of statin-related mild muscle pain since they did not result in statin intolerance; the muscle symptom was resolved with statin re-challenge. Finally, given that the study subjects were Malay ethnicity with HPL, the findings should be regarded with caution when replicated in other ethnic groups in Malaysia or healthy cohorts. In other multi-ethnic nationalities, such as Singaporeans (n = 1589), certain genetic polymorphisms were found to be associated with HDL-c levels in Chinese males alone (P = 0.004), but not in other ethnicities [51], emphasizing the importance of careful interpretation when implementing statin pharmacogenetic data across different ethnicities.

Future investigations should consider the effects variables such as smoking, alcohol intake, and BMI, which were relatively underrecognized contributors to high blood cholesterols and affecting statin response [52, 53]. The inclusion of epigenetic signatures, such as the ABCG1 gene, is particularly attractive owing to its promising signal of statins’ diabetogenic effects in a current epigenome-wide association study [54]. Furthermore, statins have been linked to epigenetic changes, particularly at genes related to lipid metabolism (i.e. ADAL gene, the most significantly differentially methylated with respect to CHD status) in subjects of European ancestry [55], and would be of clinical interest if replicated in the Asian population.