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Background: Familial sitosterolemia is a rare Mendelian disorder characterized by hyperabsorption and decreased biliary excretion of dietary sterols. Affected individuals typically have complete genetic deficiency—homozygous loss-of-function (LoF) variants—in theABCG5orABCG8genes and have substantially elevated plasma sitosterol and LDL (low-density lipoprotein) cholesterol (LDL-C) levels. The impact of partial genetic deficiency ofABCG5orABCG8—as occurs in heterozygous carriers of LoF variants—on LDL-C and risk of coronary artery disease (CAD) has remained uncertain.Methods: We first recruited 9 sitosterolemia families, identified causative LoF variants inABCG5orABCG8, and evaluated the associations of theseABCG5orABCG8LoF variants with plasma phytosterols and lipid levels. We next assessed for LoF variants inABCG5orABCG8in CAD cases (n=29 321) versus controls (n=357 326). We tested the association of rare LoF variants inABCG5orABCG8with blood lipids and risk for CAD. Rare LoF variants were defined as protein-truncating variants with minor allele frequency <0.1% inABCG5orABCG8.Results: In sitosterolemia families, 7 pedigrees harbored causative LoF variants inABCG5and 2 pedigrees inABCG8. Homozygous LoF variants in eitherABCG5orABCG8led to marked elevations in sitosterol and LDL-C. Of those sitosterolemia families, heterozygous carriers ofABCG5LoF variants exhibited increased sitosterol and LDL-C levels compared with noncarriers. Within large-scale CAD case-control cohorts, prevalence of rare LoF variants inABCG5and inABCG8was ≈0.1% each.ABCG5heterozygous LoF variant carriers had significantly elevated LDL-C levels (25 mg/dL [95% CI, 14–35];P=1.1×10⁻⁶) and were at 2-fold increased risk of CAD (odds ratio, 2.06 [95% CI, 1.27–3.35];P=0.004). By contrast,ABCG8heterozygous LoF carrier status was not associated with increased LDL-C or risk of CAD.Conclusions: Although familial sitosterolemia is traditionally considered as a recessive disorder, we observed that heterozygous carriers of an LoF variant inABCG5had significantly increased sitosterol and LDL-C levels and a 2-fold increase in risk of CAD.

The aims of this study were (1) to determine whether the accumulation of coronary plaque burden assessed with coronary computed tomography angiography (CCTA) can predict future events and (2) to estimate the onset and progression of coronary atherosclerosis in patients with familial hypercholesterolemia (FH). Consecutive 101 Japanese patients with heterozygous FH (men = 52, mean age 56 ± 16 years, mean low-density lipoprotein cholesterol 264 ± 58 mg/dl) who underwent 64-detector row CCTA without known coronary artery disease were retrospectively evaluated by assigning a score (0 to 5) to each of 17 coronary artery segments according to the Society of Cardiovascular Computed Tomography guidelines. Those scores were summed and subsequently natural log transformed. The periods to major adverse cardiac events (MACE) were estimated using multivariable Cox proportional hazards models. During the follow-up period (median 941 days), 21 MACE had occurred. Receiver operating characteristic curve analyses identified a plaque burden score of 3.35 (raw score 28.5) as the optimal cutoff for predicting a worse prognosis. Multivariate Cox regression analysis identified the presence of a plaque score ≥3.35 as a significant independent predictor of MACE (hazard ratio = 3.65; 95% confidence interval 1.32 to 25.84, p <0.05). The regression equations were Y = 0.68X - 15.6 (r = 0.54, p <0.05) in male and Y = 0.74X - 24.8 (r = 0.69, p <0.05) in female patients with heterozygous FH. In conclusion, coronary plaque burden identified in a noninvasive, quantitative manner was significantly associated with future coronary events in Japanese patients with heterozygous FH and that coronary atherosclerosis may start to develop, on average, at age 23 and 34 years in male and female patients with heterozygous FH, respectively.

Lipoprotein(a) [Lp(a)], discovered in 1963, has been associated with atherosclerotic cardiovascular disease (ASCVD) independent of other traditional risk factors, including LDL cholesterol. Lp(a) is an apolipoprotein B (apoB)-containing lipoprotein, which contains an LDL-like particle. Unlike LDL, which is a primary therapeutic target to decrease ASCVD, current guidelines recommend measuring Lp(a) for risk assessments because there is no clear evidence demonstrating the clinical benefit of decreasing Lp(a) using classical drugs such as niacin. However, recent Mendelian randomization studies indicate that Lp(a) causally correlates with ASCVD. In addition, novel drugs, including PCSK9 inhibitors, as well as antisense oligonucleotide for apo(a), have exhibited efficacy in decreasing Lp(a) substantially, invigorating a discussion whether Lp(a) could be a novel therapeutic target for further ASCVD risk reduction. This review aims to provide current understanding, and future perspectives, of Lp(a), which is currently considered a mere biomarker but may emerge as a novel therapeutic target in future clinical settings.