Abstract
Aims: Elevated lipoprotein (a) (Lp[a]), predominantly determined by genetic variability, causes atherosclerotic cardiovascular disease (ASCVD), particularly in patients with familial hypercholesterolemia (FH). We aimed to elucidate the clinical impact of Lp(a) and cumulative exposure to low-density lipoprotein cholesterol (LDL-C) on CAD in patients with FH.
Methods: One hundred forty-seven patients clinically diagnosed with heterozygous familial hypercholesterolemia (HeFH) were retrospectively investigated. Patients were divided into 2 groups according to the presence of CAD. Their clinical characteristics and lipid profiles were evaluated.
Results: There were no significant differences in untreated LDL-C levels between the 2 groups (p=0.4), whereas the cumulative exposure to LDL-C and Lp(a) concentration were significantly higher in patients with CAD (11956 vs. 8824 mg-year/dL,p＜0.01; 40 vs. 14 mg/dL,p＜0.001, respectively). A receiver operating characteristic (ROC) curve analysis demonstrated that the cutoff values of Lp(a) and cumulative LDL-C exposure to predict CAD in patients with FH were 28 mg/dL (AUC 0.71) and 10600 mg-year/dL (AUC 0.77), respectively. A multivariate analysis revealed that cumulative LDL-C exposure ≥ 10600 mg-year/dL (p＜0.0001) and Lp(a) level ≥ 28 mg/dL (p＜0.001) were independent predictors of CAD. Notably, the risk of CAD remarkably increased to 85.7% with smoking, Lp(a) ≥ 28 mg/dL, and cumulative LDL-C exposure ≥ 10600 mg-year/dL (odds ratio: 46.5, 95%CI: 5.3–411.4,p＜0.001).
Conclusions: This study demonstrated an additive effect of Lp(a) and cumulative LDL-C exposure on CAD in patients with HeFH. Interaction with traditional risk factors, particularly smoking and cumulative LDL-C exposure, enormously enhances the cardiovascular risk in this population.
Keywords: Hyper Lp(a), Heterozygous familial hypercholesterolemia, cumulative low density lipoprotein cholesterol (LDL-C) exposure, Protein convertase subtlisin/kexin type 9 (PCSK9)
Abbreviations: ASCVD: Atherosclerotic vascular disease, AT: Achilles tendon, ATT: Achilles tendon thickness, AS: Aortic stenosis, CAD: Coronary artery disease, CAG: Coronary artery angiogaphy, FH: Familial hypercholesterolemia, HeFH: Heterozygous familial hypercholesterolemia, HDL-C: High density lipoprotein cholesterol, LDL-C: Low density lipoprotein cholesterol, Lp(a): Lipoprotein (a), MDCT: Multidetector row computed tomography, PCSK9: Proprotein convertase subtilisin/kexin 9
Introduction
Familial hypercholesterolemia (FH) is a common genetic cause of premature atherosclerotic cardiovascular disease (ASCVD) owing to elevated plasma low-density lipoprotein cholesterol (LDL-C) concentrations 1) . An appropriate assessment of ASCVD risk in patients with FH can facilitate early intervention with LDL-C concentrations, further resulting in an improved prognosis in patients with FH. Previously, we reported that the addition of genetic variants, specifically the proprotein convertase subtilisin/kexin 9 (PCSK9) V4I variant with LDL receptor (LDLR) mutations 2) , Achilles tendon (AT) softness 3) , lower high-density lipoprotein cholesterol (HDL-C) concentrations 4) and cholesterol efflux capacity 5) were strongly associated with ASCVD. Despite the widespread use of established medical therapies, particularly lipid-lowering therapy, a considerable residual risk of cardiovascular events remains. Lipoprotein (a) (Lp(a)) is a low-density lipoprotein (LDL) cholesterol-like particle bound to apolipoprotein (a), and its concentration is largely genetically determined, with marked variations across populations 6) . An increasing body of evidence identifies Lp(a) as a strong independent and causal risk factor for ASCVD 7) and aortic stenosis (AS) 8) . Consequently, the risk of ASCVD is accentuated by hyper-Lp(a) in patients at high risk for ASCVD, particularly FH (i.e., the combination of cumulative exposure to elevated plasma concentrations of both Lp[a] and LDL-C appears more detrimental and increases the risk of atherosclerotic disease). Recent clinical guidelines and consensus statements recommend measuring Lp(a) levels in high-risk patient groups 9) . However, a universal absolute risk threshold remains to be established, and an estimated 20–25% of the global population has Lp(a) levels of ≥ 50 mg/dL, a level noted by the European Atherosclerosis Society to confer increased cardiovascular risk 10) .
Aim
This study investigated the prognostic value of elevated Lp(a) concentration in predicting coronary artery disease (CAD) and the clinical impact of its risk combination with traditional risk factors for CAD in Japanese patients with heterozygous familial hypercholesterolemia (HeFH).
Methods
Study Population
The present study retrospectively analyzed 147 patients who were clinically diagnosed with HeFH and underwent a coronary artery evaluation using multidetector row computed tomography (MDCT) or coronary artery angiography (CAG) at Osaka Medical and Pharmaceutical University Hospital. HeFH was diagnosed according to the guidelines of the Japan Atherosclerosis Society as follows 11) : Patients who met at least 2 of the clinical characteristic criteria, including (1) untreated LDL-C level 180 mg/dL, (2) tendon xanthoma (tendon xanthoma in the dorsal hands, elbows, and knees, or Achilles tendon thickening) or nodular xanthoma on the skin, and (3) a history of familial hypercholesterolemia or premature CAD within the first degree of relatives. Patients with Achilles tendon thickening ≥ 8 mm for males/ ≥ 7.5 mm for females on Radiography 12) or Achilles tendon thickening ≥ 6 mm for males/ ≥ 5.5 mm for females on echography 13) are considered to have xanthoma. Hypertension was defined as systolic blood pressure ≥ 140 mmHg, diastolic blood pressure ≥ 90 mmHg, or the use of antihypertensive medications. We used the definition of diabetes provided by the Japan Diabetes Society’s definition of diabetes 14) . Smoking status was defined as current smoking status. CAD was defined as the presence of at least 1 segment with ＞50% diameter stenosis in the left main coronary artery and/or ＞75% diameter stenosis in the right and/or left coronary arteries by CAG or MDCT 15) . High-intensity statins were defined as follows: atorvastatin (≥ 20 mg), rosvastatin (≥ 10 mg), and pitavastatin (≥ 4 mg). The Ethics Review Board of Osaka Medical and Pharmaceutical University approved this retrospective study and waived the requirement for informed consent (2023-066). Written informed consent is not mandatory for observational and retrospective studies. However, informed consent to perform a genetic analysis was obtained from all patients with FH who were included in the present study. All procedures were conducted in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and the 1975 Declaration of Helsinki revised in 2008.
Lipid Measurements and Genetic Variant Annotation
All lipid parameters were measured during fasting. Fasting serum levels of Lp(a), triglycerides, and high-density lipoprotein cholesterol were measured by enzymatic methods (Sekisui Medical, Tokyo, Japan) using an automated analyzer (Hitachi Labospect 008; Hitachi-Hitec, Tokyo, Japan). Low-density lipoprotein cholesterol (LDL-C) levels were calculated using the Friedewald formula, except when triglyceride levels were ＞4.5 mmol/L (400 mg/dL) 16) . The cumulative lifetime exposure to LDL-C was calculated as LDL-C max×[age at diagnosis / statin initiation]＋LDL-C at inclusion×[age at inclusion – age at diagnosis/ statin initiation] using the LDL-C exposure simulation application on the website of the Japan Atherosclerotic Society (https://www.fh-ldl-c-app.com). When informed consent was obtained, 3 classes of genetic variants (LDLR, APOB, and PCSK9) were aggregated with respect to their association with FH.
Statistical Analysis
Categorical data were summarized as frequencies and percentages and compared using Pearson’s χ2 test or Fisher’s exact test. Continuous variables were summarized as the mean±SD or median and interquartile range and compared using the Mann-Whitney test. A multivariable logistic model was used to calculate odds ratios (ORs) and 95% CIs after controlling for potential confounders. The model included risk factors that demonstrated an association with CAD in a univariate analysis. Variables that showed statistical significance in the univariate analyses were considered for inclusion in each model, and a backward selection method at alpha=0.05 was used to keep the variables in the final multivariable models. To examine the ability of Lp(a) concentration to predict CAD, receiver operating characteristic (ROC) curve analyses and calculations of sensitivity and specificity were performed. The best cutoff value for Lp(a) concentration was determined using the Youden index method. Analyses were performed using JMP 16 (SAS Institute, Cary, NC, USA).
Results
Patient Characteristics and Lipid Parameters
A total of 147 patients clinically diagnosed with FH were included in the analysis. The clinical characteristics of the study participants are summarized in Table 1 . The mean age was 46.6 years, and 64.6% of the patients were female. LDLR pathogenic variants were the dominant characteristics of genetic variants in the current study participants (LDLR: 46.9%, PCSK9:4.8%). Table 1 also illustrates the clinical characteristics of the study participants according to CAD. CAD was associated with significant differences in age and smoking status. The lipid profiles and therapies are shown in Table 2 . No significant differences were observed in untreated lipid profiles. In contrast, on-treatment LDL-C and total cholesterol levels were significantly lower in patients with CAD than in those without CAD (LDL-C: 94.2±45.1 mg/dL vs. 131.6±60.5 md/dL, p＜0.01; total cholesterol, 178.9±63.1 md/dL vs. 212.6±64.7 md/dL, p=0.03). Cumulative LDL-C exposure (11956 mg-year/dL [10609–16965] vs. 8824 mg-year/dL [6863–11222], p＜0.01) and Lp(a) concentrations (40 mg/dL (12.3 to 61) vs. 14 mg/dL [7–28 mg/dL], p＜0.001) were significantly higher in patients with CAD than in those without. While there were no significant differences in the proportions of patients receiving statins, high-intensity statins, or ezetimibe (statin: 90.9% vs. 80.8%, p=0.3; high-intensity statin: 68.2% vs. 47.2%, p=0.07, and ezetimibe: 68.2% vs. 50.4%, p=0.1), PCSK9 inhibitor and LDL apheresis were significantly higher in patients with CAD than in those without (PCSK9 inhibitor: 50% vs. 12.8%, p＜0.0001; LDL apheresis: 9.1% vs. 0%, p＜0.0001).
Table 1. Baseline patient characteristics.
| ALL (n= 147) | CAD (+) (n= 22) | CAD (-) (n= 125) | p | |
|---|---|---|---|---|
| Male, n (%) | 52 (35.4%) | 10 (45.5%) | 42 (33.6%) | 0.28 |
| Age, years | 46.6±18.3 | 63.0±13.8 | 43.9±17.6 | ＜.0001 |
| BMI, kg/m2 | 21.9±3.2 | 22.3±2.9 | 21.9±3.2 | 0.58 |
| Systolic blood pressure, mmHg | 122.7±16.3 | 122.9±12.8 | 122.7±17.1 | 0.97 |
| Diastolic blood pressure, mmHg | 70.7±11.0 | 68.1±10.8 | 71.4±11.0 | 0.27 |
| Diabetes, n (%) | 9, (6.1%) | 3 (13.6%) | 6 (4.8%) | 0.36 |
| Hb A1c, % | 5.7±0.4 | 5.8±0.3 | 5.7±0.4 | 0.19 |
| Smoking, n (%) | 50 (34.0%) | 12 (54.5%) | 38 (30.4%) | 0.032 |
| FH genotype | 0.11 | |||
| LDLR, n (%) | 69 (46.9%) | 14 (63.6%) | 55 (44%) | |
| PCSK9, n (%) | 7 (4.8%) | 0 | 7 (5.6%) |
Values are expressed mean±SD or median (interquartile range)
BMI: Body mass index
FH: Familial hypercholesterolemia
LDLR: Low density lipoprotein receptor
PCSK9: Proprotein convertase subtilisin/kexin type 9
Table 2. Lipid profiles and therapies.
| All (n= 147) | CAD (+) (n= 22) | CAD (-) (n= 125) | p | |
|---|---|---|---|---|
| Untreated lipid profiles | ||||
| LDL-C (mg/dL) | 237.4±67.8 | 252.1±77.1 | 234.3±65.8 | 0.33 |
| Total cholesterol (mg/dL) | 323.3±76.0 | 324.8±91.6 | 322.9±73.1 | 0.93 |
| Triglyceride (mg/dL) | 104.5 (75.8, 141.3) | 95 (74, 164) | 110 (76, 141) | 0.66 |
| HDL-C (mg/dL) | 57.5±17.5 | 51.1±22.2 | 58.8±16.2 | 0.12 |
| Lp(a) (mg/dL) | 15.0 (7.0, 32.0) | 40 (12.3, 61) | 14 (7, 28) | ＜.001 |
| On-treatment lipid profiles | ||||
| LDL-C (mg/dL) | 125.9±59.8 | 94.2±45.1 | 131.6±60.5 | ＜.01 |
| Total cholesterol (mg/dL) | 207.5±65.4 | 178.9±63.1 | 212.6±64.7 | 0.025 |
| Triglyceride (mg/dL) | 74.5 (58.0, 124.0) | 82.5 (60.8, 157.8) | 73.0 (55.5, 117.0) | 0.015 |
| HDL-C (mg/dL) | 60.4±14.7 | 58.3±16.1 | 60.8±14.5 | 0.47 |
| cumulative LDL-C exposure (mg-year/dL) | 9626 (7242, 11956) | 11956 (10609, 16965) | 8824 (6863, 11222) | ＜.01 |
| Therapies | ||||
| Statin, n (%) | 121 (82.3%) | 20 (90.9%) | 101 (80.8%) | 0.25 |
| High intensity statin, n (%) | 74 (50.3%) | 15 (68.2%) | 59 (47.2%) | 0.070 |
| Ezetimibe, n (%) | 78 (53.1%) | 15 (68.2%) | 63 (50.4%) | 0.12 |
| Probucol, n (%) | 2 (1.4%) | 1 (4.6%) | 1 (0.8%) | 0.16 |
| Eicosapentaenoic acid, n (%) | 6 (4.1%) | 1 (4.6%) | 5 (4.0%) | 0.91 |
| Resin, n (%) | 21 (14.3%) | 4 (18.8%) | 17 (13.6%) | 0.57 |
| PCSK9 inhibitor, n (%) | 27 (18.4%) | 11 (50%) | 16 (12.8%) | ＜.0001 |
| LDL apheresis, n (%) | 2 (1.4%) | 2 (9.1%) | 0 | ＜0.001 |
Values are expressed mean±SD or median (interquartile range)
HDL-C: High density lipoprotein cholesterol
LDL-C: Low density lipoprotein cholesterol
PCSK9: Proprotein convertase subtilisin/kexin type 9
Lp(a): Lipoprotein (a)
Carotid Intima-Media Thickness (IMT) and Achilles Tendon (AT) Thickness
Supplementary Table 1 demonstrates the comparison of carotid intima-media thickness (IMT) and Achilles tendon thickness between patients with and without CAD. The carotid IMT was significantly thicker in patients with CAD than those without (Rt: 1.3±0.7 mm vs. 0.8±0.5 mm, p＜0.001; Lt: 1.5±0.8 mm vs. 0.8±0.3 mm, p＜0.0001). The Achilles tendon thickness (ATT) derived by X-ray and echography was significantly thicker in patients with CAD than those without (X-ray Rt: 13.3±5.4 mm vs. 9.6±2.6 mm, p=0.03; Lt: 15.4±9.2 mm vs. 10.0±2.9 mm, p=0.04; maximum ATT: 10.8±5.3 mm vs. 6.6±2.4 mm, p＜0.0001). The proportion of ATT calcium levels was significantly higher in patients with CAD than in those without CAD (31.8% vs. 8.5%, p＜0.01).
Supplementary Table 1. Carotid intima-media thickness (IMT) and Achilles tendon thickness (ATT).
| All (n= 147) | CAD (+) (n= 22) | CAD (-) (n= 125) | p | |
|---|---|---|---|---|
| Carotid Intima-Media thickness (IMT) | ||||
| Max IMT Rt, (mm) | 0.9±0.5 | 1.3±0.7 | 0.8±0.5 | ＜.001 |
| Max IMT Lt, (mm) | 0.9±0.5 | 1.5±0.8 | 0.8±0.3 | ＜.0001 |
| X-ray- Achilles tendon (AT) | ||||
| Rt, (mm) | 10.1±3.4 | 13.3±5.4 | 9.6±2.6 | ＜.001 |
| Lt, (mm) | 10.9±4.9 | 15.4±9.2 | 10.0±2.9 | ＜.0001 |
| AT thickening, n (%) | 59 (40.1%) | 11 (50%) | 48 (38.4%) | 0.45 |
| Echogram- AT | ||||
| Max AT thickness, (mm) | 7.2±3.4 | 10.8±5.3 | 6.6±2.4 | ＜.0001 |
| AT thickening, n (%) | 74 (50.3%) | 17 (77.3%) | 57 (45.6%) | ＜.01 |
| AT calcium, n (%) | 17 (11.6%) | 7 (31.8%) | 10 (8.5%) | ＜.01 |
| AT xanthomas | 23 (15.6%) | 3 (13.6%) | 20 (16%) | 0.71 |
Values are expressed mean±SD
AT: Achilles tendon
IMT: Intima-Media thickness
Rt: Right
Lt: Left
Univariate and Multivariable Analyses of Factors Predicting CAD
The univariate analyses showed that age (odds ratio [OR], 1.1; 95%CI, 1.0–1.1, p＜0.0001), smoking (OR, 2.7; 95%CI, 1.1–6.8, p=0.04), hypertension (OR, 4.84; 95%CI, 1.63–14.4, p＜0.01), on-treatment LDL-C level (OR, 0.98; 95%CI, 0.97–0.99, p＜0.01), cumulative LDL-C exposure ≥ 10600 mg-year/dL (OR, 10.35; 95%CI, 2.71–39.54, p＜0.01), and Lp(a) ≥ 28 mg/dL (OR, 5.54; 95%CI, 2.12–14.48, p＜0.001) were associated with the risk of CAD. In a multivariate analysis adjusted for age, sex, smoking, hypertension, untreated LDL-C, and on-treatment LDL-C, Lp(a) ≥ 28 mg/dL was an independent predictor of CAD (Model 1: OR, 8.02; 95%CI, 1.59–40.32, p＜0.01). Another multivariable model (model 2) that included cumulative LDL-C exposure ≥ 10600 mg-year/dL revealed that hypertension, cumulative LDL-C exposure, and Lp(a) were independently associated with CAD (hypertension: OR, 5.69; 95%CI, 1.00–32.41, p=0.04; cumulative LDL-C exposure ≥ 10600 mg-year/dL: OR, 24.46; 95%CI, 3.59–166.6, p＜0.0001; and Lp(a) ≥ 28 mg/dL: OR, 13.74; 95%CI, 2.54–74.41, p＜0.001y) ( Table 3 ) .
Table 3. Uni- and Multivariate analysis for predictor of coronary artery disease.
| Univariate | Model 1 | Model 2 | |||||||
|---|---|---|---|---|---|---|---|---|---|
| OR | 95% CI | p | OR | 95% CI | p | OR | 95% CI | p | |
| Age | 1.1 | 1.0 to 1.1 | ＜.0001 | 1.09 | 1.03 to 1.16 | ＜.001 | |||
| Sex (female) | 0.6 | 0.2 to 1.5 | 0.29 | 0.20 | 0.03 to 1.30 | 0.08 | 0.25 | 0.05 to 1.36 | 0.09 |
| Smoking | 2.7 | 1.1 to 6.8 | 0.04 | 2.62 | 0.53 to 12.91 | 0.23 | 3.43 | 0.78 to 15.06 | 0.09 |
| Hypertension | 4.84 | 1.63 to 14.4 | ＜.01 | 3.79 | 0.68 to 21.17 | 0.13 | 5.69 | 1.00 to 32.41 | 0.04 |
| Diabetes mellitus | 3.75 | 0.99 to 14.09 | 0.05 | ||||||
| eGFR ＜60 mL/min/1.73m2 | 2.30 | 0.66 to 8.02 | 0.19 | ||||||
| CRP | 5.72 | 0.44 to 74.49 | 0.18 | ||||||
| Untreated | |||||||||
| LDL-C | 1.0 | 0.9 to 1.0 | 0.33 | 1.10 | 0.99 to 1.02 | 0.11 | |||
| On-treatment | |||||||||
| LDL-C | 0.98 | 0.97 to 0.99 | ＜.01 | 1.00 | 0.98 to 1.02 | 0.79 | |||
| Cumulative LDL-C exposure ≥10600 mg-year/dL | 10.35 | 2.71 to 39.54 | ＜.001 | 24.46 | 3.59 to 166.6 | ＜.0001 | |||
| Lp(a) ≥ 28 mg/dL | 5.54 | 2.12 to 14.48 | ＜.001 | 8.02 | 1.59 to 40.32 | ＜.01 | 13.74 | 2.54 to 74.41 | ＜.001 |
LDL-C: Low density cholesterol, Lp(a): Lipoprotein(a)
OR: Odds ratio
Correlation of Lp(a) and Cumulative LDL-C Exposure with CAD
A receiver-operating characteristic (ROC) curve analysis demonstrated that an Lp(a) concentration of 28 mg/dL was the threshold for predicting CAD in patients with HeFH (AUC, 0.71; sensitivity, 0.63; specificity, 0.74) ( Fig.1-a ) , and 10600 mg-year/dL was the threshold for predicting CAD in patients with HeFH (AUC, 0.77; sensitivity, 0.82; specificity, 0.69) ( Fig.1-b ) . The prevalence of CAD was further investigated in subgroups stratified according to the presence of independent predictors of CAD (smoking, Lp(a) ≥ 28 mg/dL, and cumulative LDL-C exposure ≥ 10600) ( Fig.2 ) . In patients with HeFH and smoking, Lp(a) ≥ 28 mg/dL, and cumulative LDL-C exposure ≥ 10600 alone, the prevalence of CAD was 24.0%, 31.8%, and 37.8%, respectively. Notably, the prevalence further increased to 85.7% when the risk of cumulative LDL-C exposure ≥ 10600 mg-year/dL was added to smoking and Lp(a) ≥ 28 mg/dL (OR, 46.5; 95%CI, 5.3–411.4, p＜0.001).
Fig.1.
Receiver-operating curve (ROC) analysis of the Lp(a) concentration (a) and cumulative LDL-C exposure (b) for the prediction of coronary artery disease
Fig.2. Risk of coronary artery disease (CAD) in subgroups of HeFH patients.
Lp(a): Lipoprotein (a)
Discussion
During recent decades, numerous studies have demonstrated an association between Lp(a) levels and cardiovascular events; however, its functionality and effects on atherosclerosis have not been fully elucidated. The present study investigated the prognostic value of elevated Lp(a) concentration in predicting CAD and the clinical impact of its risk combination with traditional risk factors for CAD in Japanese patients with HeFH. In the present analysis, elevated Lp(a) levels were associated with the risk of CAD in patients with HeFH. After adjusting for possible confounding factors, particularly age, smoking, and LDL-C levels, the Lp(a) level was identified as an independent predictor of the risk of CAD. Cumulative exposure to LDL-C was also independently associated with the risk of CAD in patients with HeFH, suggesting that lifelong elevation of LDL-C in HeFH confers the risk of CAD to a greater degree than that captured by a single measurement of LDL-C. An Lp(a) level of 28 mg/dL and a cumulative exposure to LDL-C of 1,600 mg/dL were thresholds for predicting CAD in HeFH patients. The combination of the risk of elevated Lp(a) levels with traditional risk factors, particularly smoking and cumulative exposure to LDL-C, dramatically increases the risk of CAD in patients with HeFH.
LDL and other lipoproteins containing apolipoprotein B (apoB) transport cholesterol and other lipids throughout the body and play a central role in the initiation and progression of atherosclerosis 17) . Given the important structural similarities between LDL and Lp(a), both are considered to be causal factors for ASCVD. Extensive observational and genetic evidence has demonstrated that a high concentration of Lp (a) is causative factor for ASCVD, AS, and cardiovascular and all-cause mortality in men and women and across ethnic groups 10 , 18) . In the present analysis, the Lp(a) concentration was significantly higher in patients with CAD than in those without CAD, consistent with previous studies demonstrating the association between hyper-Lp(a) and ASCVD. Although there is no universally accepted absolute risk threshold, the 2 main risk equations, SAFEHEART-RE and FH-Risk Score, derived from large prospective FH populations, adopted an Lp(a) concentration of 50 mg/dL as the hyper-Lp(a) variable. Indeed, it has been reported that the risk attributed to Lp(a) ≥ 50 mg/dL carries more weight than untreated LDL-C 5.5-7.5 mmol/L 19) and the atherogenicity of Lp(a) is substantially greater than that of LDL 20) . In contrast, the relative contribution of LDL and Lp(a) to cardiovascular risk appears to change with increasing levels of Lp(a), once Lp(a) levels rise above 30 mg/dL 21 , 22) . Given the differences in measurement units and techniques, the heterogeneity of the values reported in different studies and the pronounced variation in Lp(a) concentrations between different racial groups, the establishment of a universal risk cutoff value remains challenging. Our findings showing the Lp(a) concentration threshold of 28 mg/dL to predict CAD in HeFH patients may be reasonable, as the FH population has a greater risk of ASCVD due to its elevated LDL-C concentration. In this study, the risk of CAD was more than 4-fold higher in HeFH patients with an Lp(a) concentration of ≥ 28 mg/dL. However, further investigations are needed to elucidate the association between Lp(a) levels and the risk of CAD.
There is clear evidence that elevated Lp(a) is a causative factor of ASCVD, AS, and cardiovascular and all-cause mortality, particularly in patients with FH. Hyper-Lp(a) has also been reported to be more frequently seen in HeFH than in the general population 23) and Lp(a) concentrations are higher in FH (LDLR and PCSK9 mutations) than in controls 24) . Additionally, patients with a dual diagnosis of clinical HeFH and hyper-Lp(a) had the highest risk of myocardial infarction in comparison to patients with either diagnosis alone 25) , indicating that the cumulative effects of the 2 pro-atherogenic risk factors are more than additive. Given that the combination of elevated plasma concentrations of both LDL-C and Lp(a) enhances the risk of morbidity and mortality, the risk of ASCVD associated with elevated levels of Lp(a) is accentuated in patients with FH. However, FH and hyper-Lp (a) both have an autosomal dominant mode of inheritance, and the genetics of FH and hyper-Lp(a) differ. FH is a purely monogenic disorder, while elevated Lp(a) levels are a consequence of a combination of heritable factors. In our analysis, both the accumulation of risk factors for LDL-C and Lp(a) were both independently associated with CAD. Furthermore, inheriting the dual risks of HeFH and hyper-Lp(a) increased the risk of CAD to a greater extent than either diagnosis alone, consistent with a previous report 25) .
As atherosclerotic plaques grow with time, the total burden of atherosclerotic plaques is determined by both the concentration of circulating LDL-C and other lipoproteins containing apoB and the total duration of exposure to these lipoproteins 26) . Therefore, the total burden of atherosclerotic plaque is proportional to the cumulative exposure to LDL and other lipoproteins containing apoB. The effect of cumulative exposure to LDL-C on cardiovascular events in patients with FH 27 , 28) and the general population 29 , 30) has previously been validated. The cumulative LDL-C exposure score is a simple tool for evaluating the duration and intensity of vascular exposure to elevated cholesterol levels 31) . Although there is no doubt that LDL-C is a causative factor of cardiovascular disease, given that the equation represents a lifetime accumulation of exposure to LDL-C, the cumulative LDL-C exposure score may overweigh a single LDL-C measurement as a predictor of ASCVD. In fact, our findings demonstrated that the cumulative LDL-C exposure score threshold was 10,600 mg-year/dL to predict cardiovascular disease, consistent with a previous report 32) and cumulative exposure to LDL-C (but not a single LDL-C measurement) was an independent predictor of the risk of CAD. Therefore, cumulative exposure to LDL-C is considered to be a robust predictor of cardiovascular events, particularly in patients with FH. A previous study demonstrated that the increased risk of CAD appeared to be largely explained by the higher cumulative exposure to LDL-C in individuals with a variant of FH compared to those without 33) supports our findings and highlights the importance of early assessment of cardiovascular risk and the initiation of treatment.
Although the physiological function of Lp(a) has not been fully elucidated, several studies have revealed properties to underscore its potential role in the promotion of cardiovascular disease. Lp(a), an LDL-like lipoprotein consisting of a single apolipoprotein B-100 (apoB) covalently bound to apolipoprotein(a) (apo[a]) 34) , is a preferential carrier of oxidized phospholipids (OxPL) 35) , and has proatherogenic, prothrombotic and proinflammatory properties 10) . Given the functional properties of the apo(a) component, Lp(a) appears to be more atherogenic than standard LDL particles. Its OxPL content mediates proinflammatory effects, as evidenced by increased circulating and vascular levels of a range of chemokines implicated in the accumulation of inflammatory cells within the artery wall 36) . Furthermore, Lp(a) enters the arterial intima through molecular pores, where it undergoes oxidation, resulting in the formation of reactive oxygen species. The oxidized LDL portion is taken up by macrophages to generate foam cells and promote the formation of atherosclerotic plaques 37) . Smoking cigarettes also increases the oxidative modification of LDL. The circulating products of lipid peroxidation and autoantibody titers to oxidized LDL are significantly increased in smokers 38) . These studies support our findings and demonstrate an association between each risk factor and CAD. However, the impact of these multiplications on the risk of ASCVD is uncertain. We showed that cardiovascular risk was associated with hyper-Lp(a) levels and traditional risk factors, indicating that the causality for cardiovascular events was more additive.
Limitations
The present study was associated with several limitations. First, this was a retrospective observational analysis performed at a single center. The number of patients with HeFH was relatively small. Second, the decision to adopt lipid-lowering therapies was at the discretion of each physician. Therefore, a potential selection bias could not be excluded. Third, assessing the effect size of genetic variants on Lp(a) is challenging. Assays based on polyclonal antibodies have not yet been reported in terms of molar units. As many assays are hampered by calibration issues, including the isoform dependency of the test procedure and the fact that most individuals are heterozygous for Lp(a) isoforms, the accuracy of measurement of its plasma concentration is limited in the current study 39) . Fourth, differences in the maximum dose of high-intensity statin therapy between Japan and Western countries may have affected our findings. Fifth, the effect of lipid-lowering therapy, particularly the PCSK9 inhibitor, on Lp(a) levels is another limitation of the current study. Finally, the current study included Japanese patients with FH according to the Japan Atherosclerosis Society guidelines for the diagnosis of FH. Whether this analysis can be translated to non-Japanese patients with FH warrants further investigation.
Conclusion
In conclusion, this study underscores the significance of elevated Lp(a) concentrations in predicting the risk of CAD in patients with HeFH. Moreover, the interaction with traditional risk factors, particularly smoking and cumulative LDL-C exposure, enormously enhances the cardiovascular risk in this population.
Funding
This work was supported by a Labor and Welfare Sciences Research Grant for Research on Rare and Intractable Diseases (21FC0201).
Declaration of Interest
M.H-S. holds stocks of Lipid Pharmaceuticals, and has received speaking honoraria from Amgen, MEDPACE, Kowa, BML, Protosera, and Novartis. The other authors have no conflicts of interest to declare.
Author Contribution Statement
Masahito Michikura, Shinpei Fujioka, Tomohiro Fujisaka, Hideaki Morita, Yumiko Kanzaki: Writing – review and editing; Mariko Harada-Shiba: Funding acquisition, Project administration, Supervision, Writing – Review & Editing; Masaaki Hoshiga: Supervision, Writing – review and editing
Use of AI and AI-Assisted Technologies Statement
AI and AI-assisted technologies have not been used during the writing process.
Ethical Statement
The Ethics Review Board of Osaka Medical and Pharmaceutical University approved this retrospective study and waived the requirement for informed consent (2023-066). Written informed consent was not mandatory for observational and retrospective studies. However, informed consent for genetic analysis was obtained from all patients with FH included in the present study. All procedures were conducted in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and the 1975 Declaration of Helsinki revised in 2008.
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