Altered Metabolism of Low-Density Lipoprotein and Very-Low-Density Lipoprotein Remnant in Autosomal Recessive Hypercholesterolemia

Individualized Treatment for Patients With Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is one of the most common and, therefore, important inherited disorders in preventive cardiology. This disease is mainly caused by a single pathogenic mutation in the low-density lipoprotein receptor or its associated genes. Moreover, it is correlated with a high risk of cardiovascular disease. However, the phenotype severity even in this monogenic disease significantly varies. Thus, the current study aimed to describe FH and its importance and the factors (inherited and acquired) contributing to differences in phenotype severity. Different lipid-modification therapies according to these factors can lead to individualized treatments, which are also essential in the general populations.

Patient-Specific Induced Pluripotent Stem Cell-Derived Hepatocyte-Like Cells as a Model to Study Autosomal Recessive Hypercholesterolemia

Autosomal recessive hypercholesterolemia (ARH) is a rare monogenic disorder caused by pathogenic variants in the low-density lipoprotein receptor (LDLR) adaptor protein 1 (LDLRAP1) gene, encoding for the LDLRAP1 protein, which impairs internalization of hepatic LDLR. There are variable responses of ARH patients to treatment and the pathophysiological mechanism(s) for this variability remains unclear. This is in part caused by absence of reliable cellular models to evaluate the effect of LDLRAP1 mutations on the LDLRAP1 protein function and its role in LDLR internalization. Here, we aimed to validate patient-specific induced pluripotent stem cell (iPSC)-derived hepatocyte-like cells (HLCs) as an appropriate tool to model ARH disease. Fibroblasts from an ARH patient carrying the recently reported nonsense mutation, c.649G>T, were reprogrammed into hiPSCs using Sendai viral vectors. In addition, we used clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) to create an LDLRAP1 gene (also known as ARH) knockout in two different human iPSC lines. ARH patient-derived iPSCs, ARH-knockout iPSC lines, and control iPSCs were efficiently differentiated into HLCs. Western blot analysis demonstrated the absence of LDLRAP1 in HLCs derived from patient and knockout iPSCs, and this was associated with a decreased low-density lipoprotein cholesterol (LDL-C) uptake in ARH-mutant/knockout HLCs compared to control HLCs. In conclusion, we determined that the recently described c.649G>T point mutation in LDLRAP1 induces absence of the LDLRAP1 protein, similar to what is seen following LDLRAP1 knockout. This causes a decreased, although not fully absent, LDL-uptake in ARH-mutant/knockout HLCs. As knockout of LDLRAP1 or presence of the c.649G>T point mutation results in absence of LDLRAP1 protein, residual LDL uptake might be regulated by LDLRAP1-independent internalization mechanisms. Patient-specific iPSC-derived HLCs can therefore be a powerful tool to further decipher LDLRAP1 mutations and function of the protein.

Diagnosis and Management of Sitosterolemia 2021

Sitosterolemia is an inherited metabolic disorder characterized by increased levels of plant sterols, such as sitosterol. This disease is caused by loss-of-function genetic mutations in ATP-binding cassette (ABC) subfamily G member 5 or member 8 ( ABCG5 or ABCG8 , respectively), both of which play important roles in selective excretion of plant sterols from the liver and intestine, leading to failure to prevent absorption of food plant sterols. This disorder has been considered to be extremely rare. However, accumulated clinical data as well as genetics suggest the possibility of a much higher prevalence. Its clinical manifestations resemble those observed in patients with familial hypercholesterolemia (FH), including tendon xanthomas, hyper LDL-cholesterolemia, and premature coronary atherosclerosis. We provide an overview of this recessive genetic disease, diagnostic as well as therapeutic tips, and the latest diagnostic criteria in Japan.

Homozygous Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is an inherited disorder with retarded clearance of plasma LDL caused by mutations of the genes involved in the LDL receptor-mediated pathway and most of them exhibit autosomal dominant inheritance. Homozygotes of FH (HoFH) may have plasma LDL-C levels, which are at least twice as high as those of heterozygous FH (HeFH) and therefore four times higher than normal levels. Prevalence of HoFH had been estimated as 1 in 1,000,000 before but more recent genetic analysis surveys predict 1 in 170,000 to 300,000. Since LDL receptor activity is severely impaired, HoFH patients do not or very poorly respond to medications to enhance activity, such as statins, and have a poorer prognosis compared to HeFH. HoFH should therefore be clinically distinguished from HeFH. Thorough family studies and genetic analysis are recommended for their accurate diagnosis.

Fatal cardiovascular complications could develop even in the first decade of life for HoFH, so aggressive lipid-lowering therapy should be initiated as early as possible. Direct removal of plasma LDL by lipoprotein apheresis has been the principal measure for these patients. However, this treatment alone may not achieve stable LDL-C target levels and combination with drugs should be considered. The lipid-lowering effects of statins and PCSK9 inhibitors substantially vary depending on the remaining LDL receptor activity of individual patients. On the other hand, the action an MTP inhibitor is independent of LDL receptor activity, and it is effective in most HoFH cases.

This review summarizes the key clinical issues of HoFH as well as insurance coverage available under the Japanese public healthcare system.

Low-Density Lipoprotein Cholesterol Level cannot be too Low: Considerations from Clinical Trials, Human Genetics, and Biology

LDL cholesterol is by far the best established "causal" cardiovascular risk. It is distributed normally, and the mean value ranges around 100~120 mg/dl. In terms of preventive cardiology, we now know very well that the lower the LDL cholesterol, the better. Clinical usefulness of aggressive LDL-lowering therapies using statin, ezetimibe, and proprotein convertase subtilisin-kexin type 9 (PCSK9) inhibitors have been shown in primary and in secondary prevention settings. Additionally, the idea, based on recent randomized controlled trials (RCT), that the lower LDL cholesterol the better appears to be true for LDL as low as ~ 30 mg/dl. According to those data, recent guidelines in Europe and in Japan suggest the lowering of LDL cholesterol level ＜70 mg/dl for high-risk patients. However, the attainment rates of such "strict" goals seem to be quite low, probably because most cardiologists still have a sense of anxiety of "low" LDL cholesterol level. But "low" indicates no more than "lower" than the "average" range, which is not always implying the optimal range. Additionally, Mendelian randomization studies focusing on individuals exhibiting "low" LDL cholesterol suggest that "normal" LDL cholesterol levels might be too much for us. Moreover, LDL cholesterol levels of other primates are substantially lower than those in humans. In this review article, based on a series of evidence from clinical trials, human genetics, and biology, we provide the idea that we need to rethink what is the optimal range of LDL cholesterol level, instead of "normal" or "average" range.

A case of autosomal recessive hypercholesterolemia caused by a new variant in the LDL receptor adaptor protein 1 gene

We report a new variant in the LDLRAP1 gene associated with autosomal recessive hypercholesterolemia in a woman of central European ancestry.

Clinical whole exome sequencing in severe hypertriglyceridemia

BACKGROUND

Little data exist regarding the clinical application of whole exome sequencing (WES) for the molecular diagnosis of severe hypertriglyceridemia (HTG).

METHODS

WES was performed for 28 probands exhibiting severe HTG (≥1000 mg/dl) without any transient causes. We evaluated recessive and dominant inheritance models in known monogenic HTG genes, followed by disease-network gene prioritization and copy number variation (CNV) analyses to identify causative variants and a novel genetic mechanism for severe HTG.

RESULTS

We identified possible causative variants for severe HTG, including three novel variants, in nine probands (32%). In the recessive inheritance model, we identified two homozygous subjects with lipoprotein lipase (LPL) deficiency and one subject harboring compound heterozygous variants in both LPL and APOA5 genes (hyperchylomicronemia). In the dominant inheritance model, we identified probands harboring deleterious heterozygous variants in LPL, glucokinase regulatory protein, and solute carrier family 25 member 40 genes, possibly associated with this extreme HTG phenotype. However, gene prioritization and CNV analyses did not validate the novel genes associated with severe HTG.

CONCLUSIONS

In 28 probands with severe HTG, we identified potential causative variants within nine genes associated with rare Mendelian dyslipidemias. Clinical WES may be feasible for such extreme cases, potentially leading to appropriate therapies.

Oligogenic familial hypercholesterolemia, LDL cholesterol, and coronary artery disease

BACKGROUND

The genetic background of severe familial hypercholesterolemia (FH) has yet to be determined.

OBJECTIVE

We tested if genetic variants associated with low-density lipoprotein (LDL)-altering autosomal recessive diseases influenced LDL cholesterol levels and the odds for coronary artery disease in patients with high LDL cholesterol.

METHODS

We recruited 500 individuals with elevated LDL cholesterol levels (≥180 mg/dL or ≥140 mg/dL for subjects <15 years). We sequenced the exons of 3 FH genes (LDLR, apolipoprotein B, and proprotein convertase subtilisin/kexin type 9) and 4 LDL-altering accessory genes (ABCG5, ABCG8, APOE, and LDL receptor adaptor protein 1). In addition, 4 single nucleotide polymorphisms associated with polygenic FH in East Asian subjects were genotyped. Oligogenic FH patients were defined as those who harbored damaging variants of both conventional FH genes and LDL-altering accessory genes.

RESULTS

We identified damaging variants of conventional FH genes in 248 participants (50%). We also detected damaging variants in accessory genes in 57 patients (11%) and identified oligogenic FH in 27 of these patients (5%). Polygenic score in the subjects without any FH mutations was significantly higher than those in any other groups. Compared with monogenic FH, oligogenic FH exhibited significantly higher LDL cholesterol (265 mg/dL, 95% confidence interval [CI] 216-312, and 210 mg/dL, 95% CI 189-243; P = .04). Oligogenic FH exhibited higher odds for coronary artery disease when compared with monogenic FH, although it did not reach statistical significance (odds ratio 1.41, 95% CI 0.68-2.21, P = .24).

CONCLUSIONS

Among patients with elevated LDL cholesterol, those with oligogenic FH had higher LDL cholesterol than monogenic FH.

Guidance for Pediatric Familial Hypercholesterolemia 2017

This paper describes consensus statement by Joint Working Group by Japan Pediatric Society and Japan Atherosclerosis Society for Making Guidance of Pediatric Familial Hypercholesterolemia (FH) in order to improve prognosis of FH.FH is a common genetic disease caused by mutations in genes related to low density lipoprotein (LDL) receptor pathway. Because patients with FH have high LDL cholesterol (LDL-C) levels from the birth, atherosclerosis begins and develops during childhood which determines the prognosis. Therefore, in order to reduce their lifetime risk for cardiovascular disease, patients with FH need to be diagnosed as early as possible and appropriate treatment should be started.Diagnosis of pediatric heterozygous FH patients is made by LDL-C ≥140 mg/dL, and family history of FH or premature CAD. When the diagnosis is made, they need to improve their lifestyle including diet and exercise which sometimes are not enough to reduce LDL-C levels. For pediatric FH aged ≥10 years, pharmacotherapy needs to be considered if the LDL-C level is persistently above 180 mg/dL. Statins are the first line drugs starting from the lowest dose and are increased if necessary. The target LDL-C level should ideally be ＜140 mg/dL. Assessment of atherosclerosis is mainly performed by noninvasive methods such as ultrasound.For homozygous FH patients, the diagnosis is made by existence of skin xanthomas or tendon xanthomas from infancy, and untreated LDL-C levels are approximately twice those of heterozygous FH parents. The responsiveness to pharmacotherapy should be ascertained promptly and if the effect of treatment is not enough, LDL apheresis needs to be immediately initiated.

Prominent Tendon Xanthomas and Abdominal Aortic Aneurysm Associated with Cerebrotendinous Xanthomatosis Identified Using Whole Exome Sequencing

A 63-year-old man was hospitalized due to an abdominal pulsatile mass. Computed tomography revealed a saccular type abdominal aortic aneurysm, the diameter of which was 52 mm. A physical examination revealed prominent Achilles tendon thickness and plantar xanthomas. He was born in a family of consanguineous marriage, where his parents were second cousins. He had no familial history of high low-density lipoprotein cholesterol, tendon xanthomas, or premature atherosclerosis. Whole-exome sequencing assuming recessive inheritance determined his genetic diagnosis to be cerebrotendinous xanthomatosis caused by homozygous mutations (c.410G>A or p.Arg137Gln) in the cytochrome P450 subfamily 27 A1 (CYP27A1) gene.

Prominent Tendon Xanthomas and Abdominal Aortic Aneurysm Associated with Cerebrotendinous Xanthomatosis Identified Using Whole Exome Sequencing

A 63-year-old man was hospitalized due to an abdominal pulsatile mass. Computed tomography revealed a saccular type abdominal aortic aneurysm, the diameter of which was 52 mm. A physical examination revealed prominent Achilles tendon thickness and plantar xanthomas. He was born in a family of consanguineous marriage, where his parents were second cousins. He had no familial history of high low-density lipoprotein cholesterol, tendon xanthomas, or premature atherosclerosis. Whole-exome sequencing assuming recessive inheritance determined his genetic diagnosis to be cerebrotendinous xanthomatosis caused by homozygous mutations (c.410G>A or p.Arg137Gln) in the cytochrome P450 subfamily 27 A1 (CYP27A1) gene.

Remnant-like particles and coronary artery disease in familial hypercholesterolemia

BACKGROUND

Although remnant-like particle cholesterol (RLP-C) has been associated with coronary artery disease (CAD) in the general population, few data exist regarding this issue in patients with familial hypercholesterolemia (FH). The aim of our study was to investigate the association between RLP-C and the presence of CAD in patients with FH.

METHODS

We examined 282 patients with FH (144 males, mean age, 41 ± 17 years) whose RLP-C levels were measured. We assessed the baseline characteristics, including lipid levels, other conventional risk factors for cardiovascular events, the presence of CAD, and the serum RLP-C levels.

RESULTS

Serum RLP-C levels significantly correlated with serum triglyceride (TG) levels (Pearson's r = 0.631, p < 0.001). We observed that a larger proportion of individuals in the higher tertiles of serum RLP-C had a larger number of diseased coronary arteries (p < 0.001 for the trend of multi-vessel disease). Logistic regression analysis, after adjusting for age, sex, hypertension, diabetes, smoking, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and lipoprotein (a) [Lp(a)], revealed that RLP-C was significantly associated with CAD [odds ratio (OR): 1.08, 95% confidence interval (CI): 1.00-1.16, p = 0.046]; however, adding serum TG levels into the logistic regression model nullified this association (OR: 1.07, 95% CI: 0.98-1.17, p = 0.141), whereas Lp(a) was independently associated with CAD (OR: 1.02, 95% CI: 1.00-1.03, p = 0.015).

CONCLUSIONS

Serum RLP-C levels were significantly associated with the presence and severity of CAD in patients with FH. However, the clinical usefulness of measuring RLP-C levels beyond that of measuring TG levels should be further assessed.

Assessments of Carotid Artery Plaque Burden in Patients With Familial Hypercholesterolemia

Although both carotid intima-media thickness (cIMT) and carotid plaque score (cPS) determined by carotid ultrasonography reflect the severity of coronary atherosclerosis, there are few reports on direct comparisons of their clinical utilities in patients with familial hypercholesterolemia (FH). We aimed (1) to compare the clinical utilities of these measurements and (2) to estimate the onset and progression of carotid atherosclerosis in patients with FH. We examined 225 patients with FH (126 males; mean age, 51 ± 18 years) who underwent carotid ultrasonography. We assessed baseline characteristics including lipid levels, other traditional risk factors, and the presence of coronary artery disease (CAD) as well as mean cIMT and cPS. Multivariate logistic analysis revealed that cPS was significantly associated with CAD (odds ratio [OR] 1.22, 95% confidence interval (CI) 1.10-1.37, p = 0.00036), whereas cIMT was not (OR 1.26, 95% CI 0.15 to 11.76, p = 0.84). Adding cPS information to other traditional risk factors improved the risk discrimination of CAD (C-index 0.887 vs 0.909, p = 0.030), whereas adding cIMT information did not (C-index 0.887 vs 0.893, p = 0.33). Regression equations were Y = 0.219X - 3.74 (r = 0.65, p < 0.001) in male and Y = 0.215X - 5.47 (r = 0.72, p < 0.001) in female patients with FH. In conclusion, cPS may provide superior risk stratification in patients with FH compared with cIMT. On average, carotid atherosclerosis may develop at 17 and 26 years of age in male and female patients with heterozygous FH, respectively.

Molecular and functional characterization of familial chylomicronemia syndrome

BACKGROUND AND AIMS

Familial chylomicronemia syndrome is a rare autosomal recessive disorder leading to severe hypertriglyceridemia (HTG) due to mutations in lipoprotein lipase (LPL)-associated genes. Few data exist on the clinical features of the disorder or on comprehensive genetic approaches to uncover the causative genes and mutations.

METHODS

Eight patients diagnosed with familial hyperchylomicronemia with recessive inheritance were included in this study (two males and six females; median age of onset 23.0 years; mean triglyceride level 3446 mg/dl). We evaluated their clinical features, including coronary artery disease using coronary computed tomography, and performed targeted next-generation sequencing on a panel comprising 4813 genes associated with known clinical phenotypes. After standard filtering for allele frequency <1% and in silico annotation prediction, we used three types of variant filtering to identify causative mutations: homozygous mutations in known familial hyperchylomicronemia-associated genes, homozygous mutations with high damaging scores in novel genes, and deleterious mutations within 37 genes known to be associated with HTG.

RESULTS

A total of 1810 variants out of the 73,389 identified with 94.3% mean coverage (×20) were rare and nonsynonymous. Among these, our schema detected four pathogenic or likely pathogenic mutations in the LPL gene (p.Ala248LeufsTer4, p.Arg270Cys, p.Ala361Thr, and p.Val227Gly), including one novel mutation and a variant of uncertain significance. Patients harboring LPL gene mutations showed no severe atherosclerotic changes in the coronary arteries, but recurrent pancreatitis with long-term exposure to HTG was observed.

CONCLUSIONS

These results demonstrate that LPL gene plays a major role in extreme HTG associated with hyperchylomicronemia, although the condition may not cause severe atherosclerosis.

Clinical Perspectives of Genetic Analyses on Dyslipidemia and Coronary Artery Disease

We have learned that low-density lipoprotein (LDL) cholesterol is the cause of atherosclerosis from various aspects, including a single case with familial hypercholesterolemia, other cases with different types of Mendelian dyslipidemias, large-scale randomized controlled trials using LDL cholesterol lowering therapies, and Mendelian randomization studies using common as well as rare variants associated with LDL cholesterol levels. There is no doubt that determinations of genotypes in lipid-associated genes have contributed not only to the genetic diagnosis for Mendelian dyslipidemias but also to the discoveries of novel therapeutic targets. Furthermore, recent studies have shown that such genetic information could provide useful clues for the risk prediction as well as risk stratification in general and in particular population. We provide the current understanding of genetic analyses relating to plasma lipids and coronary artery disease.

Targeting microsomal triglyceride transfer protein and lipoprotein assembly to treat homozygous familial hypercholesterolemia

Homozygous familial hypercholesterolemia (HoFH) is a polygenic disease arising from defects in the clearance of plasma low-density lipoprotein (LDL), which results in extremely elevated plasma LDL cholesterol (LDL-C) and increased risk of atherosclerosis, coronary heart disease, and premature death. Conventional lipid-lowering therapies, such as statins and ezetimibe, are ineffective at lowering plasma cholesterol to safe levels in these patients. Other therapeutic options, such as LDL apheresis and liver transplantation, are inconvenient, costly, and not readily available. Recently, lomitapide was approved by the Federal Drug Administration as an adjunct therapy for the treatment of HoFH. Lomitapide inhibits microsomal triglyceride transfer protein (MTP), reduces lipoprotein assembly and secretion, and lowers plasma cholesterol levels by over 50%. Here, we explain the steps involved in lipoprotein assembly, summarize the role of MTP in lipoprotein assembly, explore the clinical and molecular basis of HoFH, and review pre-clinical studies and clinical trials with lomitapide and other MTP inhibitors for the treatment of HoFH. In addition, ongoing research and new approaches underway for better treatment modalities are discussed.

A Rare Coincidence of Sitosterolemia and Familial Mediterranean Fever Identified by Whole Exome Sequencing

Whole exome sequencing (WES) technologies have accelerated genetic studies of Mendelian disorders, yielding approximately 30% diagnostic success. We encountered a 13-year-old Japanese female initially diagnosed with familial hypercholesterolemia on the basis of clinical manifestations of severe hypercholesterolemia (initial LDL cholesterol=609 mg/dl at the age of one) and systemic intertriginous xanthomas with histories of recurrent self-limiting episodes of fever and arthritis. Both her phenotypes seemed to co-segregate in a recessive manner. We performed WES on this patient, who was considered a proband. Among 206,430 variants found in this individual, we found 18,220 nonsense, missense, or splice site variants, of which 3,087 were rare (minor allele frequency ≤ 0.01 or not reported) in 1000 Genome (Asian population). Filtering by assuming a recessive pattern of inheritance with the use of an in silico annotation prediction tool, we successfully narrowed down the candidates to the compound heterozygous mutations in the ABCG5 gene (c.1256G＞A or p.Arg419His/c.1763-1G＞A [splice acceptor site]) and to the double-compound heterozygous mutations in the MEFV gene (c.329T＞C/C or p.Leu110Pro/c.442G＞C/C or p.Glu148Val). The patient was genetically diagnosed with sitosterolemia and familial Mediterranean fever using WES for the first time. Such a comprehensive approach is useful for identifying causative mutations for multiple unrelated inheritable diseases.

Lipoprotein(a) in Familial Hypercholesterolemia With Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Gain-of-Function Mutations

BACKGROUND

It has been shown that serum lipoprotein(a) [Lp(a)] is elevated in familial hypercholesterolemia (FH) with mutation(s) of the LDL receptor (LDLR) gene. However, few data exist regarding Lp(a) levels in FH with gain-of-function mutations of the PCSK9 gene.

METHODS AND RESULTS

We evaluated 42 mutation-determined heterozygous FH patients with aPCSK9gain-of-function mutation (FH-PCSK9, mean age 52, mean LDL-C 235 mg/dl), 198 mutation-determined heterozygous FH patients with aLDLRmutation (FH-LDLR, mean age 44, mean LDL-C 217 mg/dl), and 4,015 controls (CONTROL, mean age 56, mean LDL-C 109 mg/dl). We assessed their Lp(a), total cholesterol, triglycerides, HDL-C, LDL-C, use of statins, presence of hypertension, diabetes, chronic kidney disease, smoking, body mass index (BMI) and coronary artery disease (CAD). Multiple regression analysis showed that HDL-C, use of statins, presence of hypertension, smoking, BMI, and Lp(a) were independently associated with the presence of CAD. Under these conditions, the serum levels of Lp(a) in patients with FH were significantly higher than those of the CONTROL group regardless of their causative genes, among the groups propensity score-matched (median Lp(a) 12.6 mg/dl [IQR:9.4-33.9], 21.1 mg/dl [IQR:11.7-34.9], and 5.0 mg/dl [IQR:2.7-8.1] in the FH-LDLR, FH-PCSK9, and CONTROL groups, respectively, P=0.002 for FH-LDLR vs. CONTROL, P=0.002 for FH-PCSK9 vs. CONTROL).

CONCLUSIONS

These data demonstrate that serum Lp(a) is elevated in patients with FH caused by PCSK9 gain-of-function mutations to the same level as that in FH caused by LDLR mutations.

Lipoprotein metabolism in familial hypercholesterolemia: Serial assessment using a one-step ultracentrifugation method

Objectives

It is well known that familial hypercholesterolemia (FH) is a common inherited disorder that can markedly elevate the level of plasma LDL cholesterol. However, little data exists regarding the clinical impact of the plasma triglyceride (TG)-rich lipoprotein fraction, including VLDL and IDL, in FH. Thus, we assessed the hypothesis that the mutations in the LDL receptor modulate lipoprotein metabolism other than the LDL fraction.

Design and methods

We investigated plasma lipoprotein with a one-step ultracentrifugation method for 146 controls (mean age=61.4±17.1 yr, mean LDL cholesterol=92.7±61.2 mg/dl), 213 heterozygous mutation-determined FH subjects (mean age=46.0±18.0 yr, mean LDL cholesterol=225.1±61.2 mg/dl), and 16 homozygous/compound heterozygous mutation-determined FH subjects (mean age=26.9±17.1 yr, mean LDL cholesterol=428.6±86.1 mg/dl). In addition, we evaluated cholesterol/TG ratio in each lipoprotein fraction separated by ultracentrifugation.

Results

In addition to total cholesterol and LDL cholesterol levels, VLDL cholesterol (19.5±10.4, 25.2±19.3, 29.5±21.4 mg/dl, respectively) and IDL cholesterol (8.3±3.7, 16.8±11.5, 40.0±37.3 mg/dl, respectively) exhibited a tri-model distribution according to their status in LDL receptor mutation(s). Moreover, the ratios of cholesterol/TG of each lipoprotein fraction increased significantly in heterozygous FH and homozygous/compound heterozygous FH groups, compared with that of controls, suggesting that the abnormality in LDL receptor modulates the quality as well as the quantity of each lipoprotein fraction.

Conclusions

Our results indicate that cholesterol in TG-rich lipoproteins, including VLDL and IDL, are significantly higher in FH subjects, revealing a tri-modal distribution according to the number of LDL receptor mutations.

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TG-rich lipoproteins are elevated in FH subjects.

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Such lipoproteins reveal tri-modal distribution according to the number of mutations.

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One-step ultracentrifugation is useful to assess lipoprotein abnormalities in FH.

Assessment of coronary atherosclerosis in patients with familial hypercholesterolemia by coronary computed tomography angiography

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.

Infantile Cases of Sitosterolaemia with Novel Mutations in the ABCG5 Gene: Extreme Hypercholesterolaemia is Exacerbated by Breastfeeding

Few data exists regarding the clinical impact of breastfeeding in infantile sitosterolaemic cases. We report four Japanese infantile cases of sitosterolaemia, an extremely rare inherited disease characterised by increased serum levels of plant sitosterol, presenting with severe hypercholesterolaemia and systemic xanthomas exacerbated by breastfeeding. In these four cases, genetic analyses were performed for low-density lipoprotein (LDL) receptor, proprotein convertase subtilisin/kexin type 9 (PCSK9), LDL receptor adaptor protein 1 and ATP-binding cassette (ABC) subfamily G member 5 and 8 (ABCG5 and ABCG8) genes. We assessed their clinical manifestations, including responsiveness to a variety of treatments, especially to weaning from breastfeeding and use of ezetimibe. Two pairs of mutations in the ABCG5 gene in each case, including two novel mutations (c.130C>T or p.Ser44Ala and c.1813_1817delCTTTT or p.Pro558GlufsX14) and two known mutations (c.1306G>A or p.Arg389His and c.1336C>T or p.Arg446X), were identified. Significant reductions in cholesterol levels were obtained by means of weaning from breastfeeding alone. Substantial reductions in sitosterol levels, without any apparent side effects, were observed with ezetimibe. In conclusion, we have identified infantile Japanese sitosterolaemic subjects with extreme hypercholesterolaemia exacerbated by breastfeeding. Their unique response to weaning from breastfeeding, as well as to use of ezetimibe, could provide insights into the metabolic basis of sterols in humans.

The history of Autosomal Recessive Hypercholesterolemia (ARH). From clinical observations to gene identification

The most frequent form of monogenic hypercholesterolemia, also known as Familial Hypercholesterolemia (FH), is characterized by plasma accumulation of cholesterol transported in Low Density Lipoproteins (LDLs). FH has a co-dominant transmission with a gene-dosage effect. FH heterozygotes have levels of plasma LDL-cholesterol (LDL-C) twice normal and present xanthomas and coronary heart disease (CHD) in adulthood. In rare FH homozygotes plasma LDL-C level is four times normal, while xanthomas and CHD are present from infancy. Most FH patients are carriers of mutations of the LDL receptor (LDLR); a minority of them carry either mutations in the Apolipoprotein B (ApoB), the protein constituent of LDLs which is the ligand for LDLR, or gain of function mutations of PCSK9, the protein responsible for the intracellular degradation of the LDLR. From 1970 to the mid 90s some publications described children with the clinical features of homozygous FH, who were born from normocholesterolemic parents, strongly suggesting a recessive transmission of FH. In these patients the involvement of LDLR and APOB genes was excluded. Interestingly, several patients were identified in the island of Sardinia (Italy), whose population has a peculiar genetic background due to geographical isolation. In this review, starting from the early descriptions of patients with putative recessive hypercholesterolemia, we highlight the milestones that led to the identification of a novel gene involved in LDL metabolism and the characterization of its encoded protein. The latter turned out to be an adaptor protein required for the LDLR-mediated endocytosis of LDLs in hepatocytes. The loss of function of this protein is the cause of Autosomal Recessive Hypercholesterolemia (ARH).

Pharmacological treatment of a Sardinian patient affected by Autosomal Recessive Hypercholesterolemia (ARH)

BACKGROUND AND AIM

Previous studies have shown that patients with autosomal recessive hypercholesterolemia (ARH) resulting from mutations in LDLRAP1 gene have a less severe cardiovascular involvement than familial hypercholesterolemia homozygotes, lower levels of low-density lipoprotein cholesterol (LDL-C), and higher levels of high-density lipoprotein cholesterol (HDL-C). In addition, ARH patients seem to be more responsive to the lipid-lowering drugs. The aim was to test the effect of a combined drug treatment in an ARH patient in the absence of plasmapheresis.

METHODS AND RESULTS

Here we report the lipid-lowering effect of rosuvastatin (60 mg/day) associated with ezetimibe (10 mg/day) in a single ARH patient. The sequencing of LDLRAP1 gene showed that the patient was homozygous for the c.432insA mutation. During a 6-month treatment, we observed an 80% reduction of LDL-C and a significant increase of HDL-C and ApoA-I. Some sequence variations in PCSK9 and NPC1L1 genes found in this patient may have contributed to the success of drug treatment.

CONCLUSIONS

Our findings, although limited to a single case, suggest that in many ARH patients the LDL-C goal may be reached with the more potent statins associated with ezetimibe in the absence of extracorporeal procedures.

Autosomal recessive hypercholesterolemia: a mild phenotype of familial hypercholesterolemia: insight from the kinetic study using stable isotope and animal studies

Autosomal recessive hypercholesterolemia (ARH) is an extremely rare inherited disorder, the cause of which is mutations in the low-density lipoprotein (LDL) receptor adaptor protein 1 (LDLRAP1) gene. Only 36 families with 14 different mutations have been reported in the literature to date. The clinical phenotype of ARH is milder than that of homozygous familial hypercholesterolemia (FH) caused by LDL receptor gene mutations. Recently, the lipoprotein metabolism of ARH was investigated in both humans and mice by several investigators, including ourselves. Based on these findings the preserved clearance of LDL receptor-dependent very-LDL (VLDL) may be a possible mechanism underlying the responsiveness to statins and the milder phenotype of ARH. Although ARH has been described as being "recessive," several studies, including ours, have indicated that a heterozygous carrier status of the LDLRAP1 gene is associated with mild hypercholesterolemia and exacerbates the phenotype of FH resulting from LDL receptor gene mutations. This review summarizes current understanding regarding ARH and its causative gene, LDLRAP1, and attempts to provide new insight into novel pharmacological targets for treating dyslipidemic patients.

Current perspectives in genetic cardiovascular disorders: from basic to clinical aspects

We summarize recent advances in the clinical genetics of hypercholesterolemia, hypertrophic cardiomyopathy (HCM), and lethal arrhythmia, all of which are monogenic cardiovascular diseases being essential to understanding the heart and circulatory pathophysiology. Among the issues of hypercholesterolemia which play a pivotal role in development of vascular damages, familial hypercholesterolemia is the common genetic cardiovascular disease; in addition to identifying the gene mutation coding low-density lipoprotein receptor, lipid kinetics in autosomal recessive hypercholesterolemia as well as in proprotein convertase subtilisin/kexin 9 gene mutation were recently demonstrated. As for HCM, some gene mutations were identified to correlate with clinical manifestations. Additionally, a gene polymorphism of the renin-angiotensin system in development of heart failure was identified as a modifier gene. The lethal arrhythmias such as sudden death syndromes, QT prolongation, and Brugada syndrome were found to exhibit gene mutation coding potassium and/or sodium ion channels. Interestingly, functional analysis of these gene mutations helped to identify the role of each gene mutation in developing these cardiovascular disorders. We suggest considering the genetic mechanisms of cardiovascular diseases associated with hyperlipidemia, myocardial hypertrophy, or lethal arrhythmia in terms of not only clinical diagnosis but also understanding pathophysiology of each disease with therapeutic aspects.

Recent advances in the treatment of homozygous familial hypercholesterolaemia

PURPOSE OF REVIEW

To review publications in the English literature over the past 18 months relating to the management of homozygous familial hypercholesterolaemia.

RECENT FINDINGS

Experience with plasmapheresis has been summarized, guidelines are being introduced to enhance patient care and registries are under consideration to improve analysis of management in this rare but serious disorder. Liver transplantation has been reviewed for its biochemical efficacy, but still does not ensure freedom from vascular complications. For patients without access to plasmapheresis, there is now evidence that high-dose statins do improve the prognosis, but combination therapy with additional agents should still be considered for better outcome. Promising new agents that inhibit LDL production by limiting apolipoprotein B100 synthesis by means of antisense oligonucleotides (mipomersen) or by inhibition of microsomal triacylglycerol transfer protein (lomitapide) have made significant additional LDL reduction possible but are associated with hepatic fat accumulation and long-term safety data is still required. Several other lipid modulating agents and gene therapy are still being explored.

SUMMARY

The management of homozygous familial hypercholesterolaemia by pharmacological means is improving with agents that limit lipoprotein production but plasmapheresis, generally in combination with additional pharmacological treatment, remains the proven option. Liver transplantation is now less likely to be undertaken owing to improved pharmacological options and prognosis.

Lipoprotein kinetics in male hemodialysis patients treated with atorvastatin

BACKGROUND AND OBJECTIVES

In vivo metabolism of atherogenic apolipoprotein B (apoB)-containing lipoproteins is severely impaired in patients undergoing hemodialysis (HD), resulting in markedly prolonged residence times of these particles. It is unclear whether treatment with statins improves LDL kinetics in HD patients as is known for the general population. Therefore, this kinetic study assessed apoB-containing lipoproteins in these patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Kinetic measures were analyzed with stable-isotope technology in six men undergoing HD before and after 3 months of daily administration of 10 mg of atorvastatin. Patients were 18-65 years of age, had LDL cholesterol levels between 90 and 200 mg/dl, and had been treated with HD for >6 months. They consumed a standardized isocaloric diet for 3 days before analysis. Fractional catabolic rates (FCRs) and production rates of very-low-density lipoprotein (VLDL)-apoB, intermediate-density lipoprotein-apoB, and LDL-apoB were determined using multicompartment modeling after plasma lipoprotein separation, precipitation of apoB, and determination of tracer-to-tracee ratios using mass spectrometry.

RESULTS

Plasma concentrations of VLDL- and LDL-apoB were significantly lower (mean ± SD, 7.77±2.62 versus 11.27±6.15 mg/dl, P<0.05; 56.9±23.9 versus 84.0±21.1 mg/dl, P=0.03) and their FCRs were significantly higher (7.20±3.08 versus 5.20±2.98 days(-1), P<0.05; 0.851±0.772 versus 0.446±0.232 days(-1), P<0.05) after 3 months of atorvastatin treatment. Accordingly, the residence times in plasma of VLDL- and LDL-apoB were significantly lower after treatment (0.14 versus 0.19 day and 1.2 versus 2.2 days, respectively).

CONCLUSION

Lower plasma concentrations and improved kinetics of atherogenic lipoproteins were observed in HD patients after administration of low-dose atorvastatin.

Post-prandial remnant lipoprotein metabolism in autosomal recessive hypercholesterolaemia

BACKGROUND

Phenotype of autosomal recessive hypercholesterolaemia (ARH), a rare lipid disorder, is known to be milder than that of homozygous familial hypercholesterolaemia (FH) with LDL receptor gene mutation. However, few data exist regarding the functional differences in ARH and FH particularly in terms of remnant-like particles' (RLP) metabolism.

MATERIALS AND METHODS

Blood sampling was performed up to 6h after OFTT cream loading (50 g/body surface area) with 2-h intervals in a single ARH proband, four heterozygous FH patients with LDL receptor gene mutation and four normal controls. Plasma lipoprotein and RLP fraction were determined by HPLC system. The area under curve (AUC) of each lipoprotein including RLP fractions was evaluated.

RESULTS

The AUC of TG, RLP cholesterol (RLP-C) and RLP triglyceride (RLP-TG) levels of heterozygous FH subjects was significantly higher than those of controls (466±71 mg/dL×h vs. 303±111 mg/dL×h, P<0·05; 35±7 mg/dL×h vs. 21±8 mg/dL×h, P<0·05; 124±57 mg/dL×h vs. 51±13 mg/dL×h, P<0·05, respectively). Under these conditions, those values of ARH were close to those of controls (310 mg/dL×h, 22 mg/dL×h, 23 mg/dL×h, respectively).

CONCLUSION

These data demonstrate that unlike in FH, RLP clearance is preserved in ARH. The preservation of post-prandial RLP clearance may contribute to the mild phenotype of ARH compared with FH.