Sitosterolemia, Hypercholesterolemia, and Coronary Artery Disease

Prospective Registry Study of Primary Dyslipidemia (PROLIPID): Rationale and Study Design

Introduction: Primary dyslipidemias are inherited disorders in plasma lipoprotein metabolism that lead to serious cardiovascular and other complications. The Japanese Ministry of Health, Labor and Welfare (MHLW) covers medical expenses, under the Research Program on Rare and Intractable Diseases, for homozygous familial hypercholesterolemia (FH), familial chylomicronemia, sitosterolemia, cerebrotendinous xanthomatosis, lecithin:cholesterol acyltransferase deficiency, Tangier disease, and abetalipoproteinemia. Apolipoprotein A1 deficiency, heterozygous FH, and type III hyperlipoproteinemia are covered by the MHLW Pediatric Chronic Disease Program. Heterozygous FH and type III hyperlipoproteinemia are also important for their relatively common prevalence and, accordingly, high impact on Japanese public health by significant contribution to the overall prevalence of cardiovascular diseases. Therefore, a systemic survey of these diseases is mandatory to estimate their actual situation, such as prevalence, clinical manifestations, and prognoses among the Japanese population. The impact of these rare and intractable diseases on cardiovascular and other complications will likely be higher among Japanese people than other ethnicities because the general Japanese population has many cardioprotective aspects. The current study intends to conduct a multicenter registry of these diseases to assess their demographics and clinical features comprehensively.

Methods and Analysis: The Prospective Registry Study of Primary Dyslipidemia is a registry-based prospective, observational, multicenter cohort study in Japan, enrolling patients who fulfill the Japanese clinical criteria of the primary dyslipidemias listed above, from 26 participating institutes from August 2015 to March 2023. A total of 1,000 patients will be enrolled in the study and followed for 10 years. Clinical parameters are collected, including physical and laboratory findings, genetic analysis, drugs, lifestyle management, and clinical events, especially cardiovascular events. The primary endpoint of this study is the new onset of cardiovascular disease and acute pancreatitis, and the secondary endpoint is death from any causes.

Ethics and Dissemination: This study complies with the Declaration of Helsinki, the Ethical Guidelines for Medical and Health Research Involving Human Subjects, and all other applicable laws and guidelines in Japan. The institutional review boards have approved this study protocol at all participating institutes. The final results are to be published at appropriate international conferences and in peer-reviewed journals.

Premature Acute Myocardial Infarction in a Young Patient With Sitosterolemia

Sitosterolemia is a rare, inherited, autosomal recessive disorder of lipid metabolism characterized by increased levels of plant sterols, such as sitosterol and campesterol, xanthomas, and accelerated atherosclerosis. In a 15-year-old boy exhibiting ST-elevation acute myocardial infarction, lipid panels, including plant sterol, and genetic testing for the ATP-binding cassette sub-family G member 5 (ABCG5) gene mutation, confirmed the diagnosis of sitosterolemia. A comprehensive lipid panel and genetic testing should be considered in patients with premature coronary artery disease to prevent disease progression through dietary and pharmacologic interventions specific to sitosterolemia.

ATP-binding cassette (ABC) transporters in cancer: A review of recent updates

The ATP-binding cassette (ABC) transporter superfamily is one of the largest membrane protein families existing in wide spectrum of organisms from prokaryotes to human. ABC transporters are also known as efflux pumps because they mediate the cross-membrane transportation of various endo- and xenobiotic molecules energized by ATP hydrolysis. Therefore, ABC transporters have been considered closely to multidrug resistance (MDR) in cancer, where the efflux of structurally distinct chemotherapeutic drugs causes reduced itherapeutic efficacy. Besides, ABC transporters also play other critical biological roles in cancer such as signal transduction. During the past decades, extensive efforts have been made in understanding the structure-function relationship, transportation profile of ABC transporters, as well as the possibility to overcome MDR via targeting these transporters. In this review, we discuss the most recent knowledge regarding ABC transporters and cancer drug resistance in order to provide insights for the development of more effective therapies.

Phytosterol accumulation results in ventricular arrhythmia, impaired cardiac function and death in mice

Heart failure (HF) and cardiac arrhythmias share overlapping pathological mechanisms that act cooperatively to accelerate disease pathogenesis. Cardiac fibrosis is associated with both pathological conditions. Our previous work identified a link between phytosterol accumulation and cardiac injury in a mouse model of phytosterolemia, a rare disorder characterized by elevated circulating phytosterols and increased cardiovascular disease risk. Here, we uncover a previously unknown pathological link between phytosterols and cardiac arrhythmias in the same animal model. Phytosterolemia resulted in inflammatory pathway induction, premature ventricular contractions (PVC) and ventricular tachycardia (VT). Blockade of phytosterol absorption either by therapeutic inhibition or by genetic inactivation of NPC1L1 prevented the induction of inflammation and arrhythmogenesis. Inhibition of phytosterol absorption reduced inflammation and cardiac fibrosis, improved cardiac function, reduced the incidence of arrhythmias and increased survival in a mouse model of phytosterolemia. Collectively, this work identified a pathological mechanism whereby elevated phytosterols result in inflammation and cardiac fibrosis leading to impaired cardiac function, arrhythmias and sudden death. These comorbidities provide insight into the underlying pathophysiological mechanism for phytosterolemia-associated risk of sudden cardiac death.

Genetic basis and hematologic manifestations of sitosterolemia in a group of Turkish patients

BACKGROUND

Sitosterolemia is a rare lipid disorder caused by mutations in adenosine triphosphate-binding cassette genes (ABCG) 5 and 8.

OBJECTIVE

To evaluate the phenotypic/genotypic features of sitosterolemia in a group of Turkish patients.

METHODS

Seven probands with unexplained hematologic abnormalities and their 13 relatives were enrolled. Sterol levels were measured by gas chromatography and genetic studies were performed using Sanger sequencing. Individuals were diagnosed with sitosterolemia if they were found to have frankly elevated sitosterol level >15 μg/mL and/or pathogenic variants of the ABCG5/ABCG8.

RESULTS

The seven probands and their six relatives  were diagnosed with frank sitosterolemia, and all these patients had hematologic abnormalities. The remaining seven relatives were asymptomatic heterozygous carriers. Three novel variants in the ABCG5 gene (c.161G>A, c.1375C>T, IVS10-1G>T), one novel variant in the ABCG8 gene (c.1762G>C) and one known variant in the ABCG5 gene (c.1336 C>T) were identified. No variant was identified in one case. The mean sitosterol level was significantly higher and mean platelet count was significantly lower in patients with homozygous variants compared to heterozygous variants (p<0.05, for all). Diets low in plant sterols were recommended for 13 symptomatic cases. Four homozygotes received ezetimibe, and their splenomegaly, anemia, and thrombocytopenia completely resolved except one.

CONCLUSION

The five pathogenic variants identified in this study indicate the genetic heterogeneity of sitosterolemia in Turkish population. Patients with unexplained hematologic abnormalities (specifically macrothrombocytopenia) should have their sterol level measured as initial testing. Ezetimibe can be a good choice for sitosterolemia.

A service evaluation: impact of nurse-led regional familial hypercholesterolaemia service on a hospital adult lipid clinic

The authors evaluated the impact of genetic screening for familial hypercholesterolaemia (FH) in a lipid clinic cohort of patients with definite and possible FH as defined by the Simon Broome Register (SBR) criteria.

METHODS

Patients with a lipid clinic diagnosis of definite and possible FH based on the SBR criteria were referred to a nurse-led regional service for FH genetic testing.

FINDINGS

140 patients were referred for genetic testing. Six had SBR-definite FH due to the presence of tendon xanthomata and 134 had SBR-possible FH. A monogenic FH mutation was detected in all six patients (100%) with SBR-definite FH and in 34 (25%) of patients with possible FH.

CONCLUSION

The appropriate use of molecular genetics in a lipid clinic will greatly facilitate the management of hyperlipidaemia and cardiovascular risk since the management of FH patients (National Institute for Health and Care Excellence (NICE) Clinical Guideline 71) is different from non-FH patients (NICE Clinical Guideline 181).

High-Fat Diet Enhances Neutrophil Adhesion in LDLR-Null Mice Via Hypercitrullination of Histone H3

Neutrophil adhesion on the atheroprone femoral artery of high-fat diet-fed low-density lipoprotein receptor-null mice was enhanced more than in wild-type mice. The inhibition of histone H3 citrullination of neutrophils reversed the enhancement of neutrophil adhesion, suggesting that hypercitrullination contributes to enhanced neutrophil adhesion. Furthermore, pemafibrate reduced the citrullination of histone H3 in these mice. Therefore, the hypercitrullination of histone H3 in neutrophils contributes to atherosclerotic vascular inflammation.

Cerebrotendinous Xanthomatosis: Molecular Pathogenesis, Clinical Spectrum, Diagnosis, and Disease-Modifying Treatments

Cerebrotendinous xanthomatosis (CTX) is an autosomal recessive lipid storage disorder caused by mutations in the CYP27A1 gene, which encodes the mitochondrial enzyme sterol 27-hydroxylase. Decreased sterol 27-hydroxylase activity results in impaired bile acid synthesis, leading to reduced production of bile acids, especially chenodeoxycholic acid (CDCA), as well as elevated serum cholestanol and urine bile alcohols. The accumulation of cholestanol and cholesterol mainly in the brain, lenses, and tendons results in the characteristic clinical manifestations of CTX. Clinical presentation is characterized by systemic symptoms including neonatal jaundice or cholestasis, refractory diarrhea, juvenile cataracts, tendon xanthomas, osteoporosis, coronary heart disease, and a broad range of neuropsychiatric manifestations. The combinations of symptoms vary from patient to patient and the presenting symptoms, especially in the early disease phase, may be nonspecific, which leads to a substantial diagnostic delay or underdiagnosis. Replacement of CDCA has been approved as a first-line treatment for CTX, and can lead to biochemical and clinical improvements. However, the effect of CDCA treatment is limited once significant neuropsychiatric manifestations are established. The age at diagnosis and initiation of CDCA treatment correlate with the prognosis of patients with CTX. Therefore, early diagnosis and subsequent treatment initiation are essential.

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.

Challenges of Precision Medicine for Atherosclerotic Cardiovascular Disease Based on Human Genome Information

Precision or personalized medicine is currently gaining a lot of attention. Clinical evidence for its effectiveness has been established based on randomized clinical trials accounting for classical risk factors, such as hypertension, diabetes, and serum lipids. However, besides such classical risk factors, the genetic background should be considered, at least for heritable traits, including atherosclerotic cardiovascular disease (ASCVD). Such classical risk factors are almost always incidents that have already occurred in which it may be too late to start treatment, instead of indicators of presymptomatic state. Human genome information is associated with most traits, including ASCVD. Two methods of implementing precision medicine for ASCVD using human genome information are currently being investigated: the use of rare genetic variations that have large effect sizes and polygenic risk scores that are composed of multiple common genetic variations. This review article emphasizes the importance of clinical as well as genetic diagnoses when implementing precision medicine. Precision medicine should be considered based on comprehensive genetic analyses, encompassing rare to common genetic variations.

Sitosterolemia: Four Cases of an Uncommon Cause of Hemolytic Anemia (Mediterranean Stomatocytosis with Macrothrombocytopenia)

Sitosterolemia is a rare autosomal recessively inherited lipid metabolic disorder that is characterized by hyper absorption of plant sterols from the intestinal mucosa leading to toxic levels in the blood. Four patients of age ranging from 11 to 29 years presented to the outpatient department with clinical features of hemolytic anemia. There were no features of hypercholesterolemia in any of the patients. Peripheral smear examination of all four patients showed stomatocytes and macrothrombocytopenia. Qualitative testing for plant sterols was performed in one case. Next generation sequencing revealed a compound heterozygous mutation in ABCG5 gene (c.1222C>T and c.1255C>T) in one case and homozygous mutations in ABCG5 gene (c.727C>T), (c.332G>A (p.G111E)), (c.1222C>T) in the other three cases. Ezetimibe (10 mg/day) was administered in one case, with complete resolution of symptoms. All patients were advised a low plant sterol diet and regular monitoring of hemoglobin and lipid profile. Our cases highlight a rare but important cause of hemolytic anemia that can be suspected from careful peripheral blood examination but only conclusively established by molecular genetic diagnosis.

Familial Hypercholesterolemia: A Narrative Review on Diagnosis and Management Strategies for Children and Adolescents

Familial hypercholesterolemia (FH) is a relatively common inherited disorder caused by deleterious mutation(s) in the low-density lipoprotein (LDL) receptor or its associated genes. Given its nature as a heritable disease, any useful screening scheme, including universal, and cascade screening, allows for the early identification of patients with FH. Another important aspect to note is that early diagnosis associated with appropriate treatment can promote better prognosis. However, most clinical diagnostic criteria for adults have adopted clinical elements, such as physical xanthomas and family history, both of which are usually obscure and/or difficult to obtain in children and adolescents. Moreover, LDL cholesterol levels fluctuating considerably during adolescence, hindering the timely diagnosis of FH. In addition, recent advancements in human genetics have revealed several types of FH, including conventional monogenic FH, polygenic FH caused by common single nucleotide variations (SNV) accumulation associated with elevated LDL cholesterol, and oligogenic FH with multiple deleterious genetic variations leading to substantially elevated LDL cholesterol. The aforementioned findings collectively suggest the need for amassing information related to genetics and imaging, in addition to classical clinical elements, for the accurate diagnosis of FH in this era of personalized medicine. The current narrative review summarizes the current status of the clinical and genetic diagnosis of FH in children and adolescents, as well as provide useful management strategies for FH in children and adolescents based on currently available clinical evidence.

Sitosterolemia Exhibiting Severe Hypercholesterolemia with Tendon Xanthomas Due to Compound Heterozygous ABCG5 Gene Mutations Treated with Ezetimibe and Alirocumab

We herein report a rare case presenting with severe hypercholesterolemia, massive Achilles tendon xanthomas, and multi-vessel coronary artery disease. Initially, the patient was misdiagnosed with familial hypercholesterolemia. However, a genetic analysis using our custom sequencing panel covering genes associated with Mendelian lipid disorders revealed him to have a genetic basis of sitosterolemia with compound heterozygous mutations in the adenosine triphosphate binding cassette subfamily G5 (ABCG5) gene. A comprehensive genetic analysis can be particularly useful for diagnosing cases with severe phenotypes, leading to appropriate and medical therapies. Our patient was refractory to statins, whereas ezetimibe and PCSK9 inhibitor with a low-plant-sterol diet successfully reduced his serum levels of low-density lipoprotein cholesterol.

Targeted Genetic Analysis in a Chinese Cohort of 208 Patients Related to Familial Hypercholesterolemia

AIM

Familial hypercholesterolemia (FH) is the most commonly encountered genetic condition that predisposes individuals to severe autosomal dominant lipid metabolism dysfunction. Although more than 75% of the European population has been scrutinized for FH-causing mutations, the genetic diagnosis proportion among Chinese people remains very low (less than 0.5%). The aim of this study was to identify genetic mutations and help make a precise diagnosis in Chinese FH patients.

METHODS

We designed a gene panel containing 20 genes responsible for FH and tested 208 unrelated Chinese possible/probable or definite FH probands. In addition, we called LDLR copy number variation (CNVs) with the panel data by panelcn.MOPS, and multiple ligation-dependent probe amplification (MLPA) was used to search for CNVs in LDLR, APOB, and PCSK9.

RESULTS

A total of 79 probands (38.0%) tested positive for a (likely) pathogenic mutation, most of which were LDLR mutations, and three LDLR CNVs called from the panel data were all successfully confirmed by MLPA analysis. In total, 48 different mutations were identified, including 45 LDLR mutations, 1 APOB mutation, 1 ABCG5 mutation, and 1 APOE mutation. Among them, the five most frequent mutations (LDLR c.1879G＞A, c.1747C＞T, c.313＋1G＞A, c.400T＞C, and APOB c.10579C＞T) were detected. Moreover, we also found that patients with LDLR variants of CNVs and splicing and nonsense had increased low-density lipoprotein cholesterol levels when compared with those who carried missense variants.

CONCLUSIONS

The spectrum of FH-causing mutations in the Chinese population is refined and expanded. Analyses of FH causal genes have been a great help in clinical diagnosis and have deep implications in disease treatment. These data can serve as a considerable dataset for next-generation sequencing analysis of the Chinese population with FH and contribute to the genetic diagnosis and counseling of FH patients.

A case of ezetimibe-effective hypercholesterolemia with a novel heterozygous variant in ABCG5

Sitosterolemia is caused by homozygous or compound heterozygous gene mutations in either ATP-binding cassette subfamily G member 5 (ABCG5) or 8 (ABCG8). Since ABCG5 and ABCG8 play pivotal roles in the excretion of neutral sterols into feces and bile, patients with sitosterolemia present elevated levels of serum plant sterols and in some cases also hypercholesterolemia. A 48-year-old woman was referred to our hospital for hypercholesterolemia. She had been misdiagnosed with familial hypercholesterolemia at the age of 20 and her serum low-density lipoprotein cholesterol (LDL-C) levels had remained about 200-300 mg/dL at the former clinic. Although the treatment of hydroxymethylglutaryl-CoA (HMG-CoA) reductase inhibitors was ineffective, her serum LDL-C levels were normalized by ezetimibe, a cholesterol transporter inhibitor. We noticed that her serum sitosterol and campesterol levels were relatively high. Targeted analysis sequencing identified a novel heterozygous ABCG5 variant (c.203A>T; p.Ile68Asn) in the patient, whereas no mutations were found in low-density lipoprotein receptor (LDLR), proprotein convertase subtilisin/kexin type 9 (PCSK9), or Niemann-Pick C1-like intracellular cholesterol transporter 1 (NPC1L1). While sitosterolemia is a rare disease, a recent study has reported that the incidence of loss-of-function mutation in the ABCG5 or ABCG8 gene is higher than we thought at 1 in 220 individuals. The present case suggests that serum plant sterol levels should be examined and ezetimibe treatment should be considered in patients with hypercholesterolemia who are resistant to HMG-CoA reductase inhibitors.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

Heterozygous ABCG5 Gene Deficiency and Risk of Coronary Artery Disease

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 the ABCG5 or ABCG8 genes and have substantially elevated plasma sitosterol and LDL (low-density lipoprotein) cholesterol (LDL-C) levels. The impact of partial genetic deficiency of ABCG5 or ABCG8-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 in ABCG5 or ABCG8, and evaluated the associations of these ABCG5 or ABCG8 LoF variants with plasma phytosterols and lipid levels. We next assessed for LoF variants in ABCG5 or ABCG8 in CAD cases (n=29 321) versus controls (n=357 326). We tested the association of rare LoF variants in ABCG5 or ABCG8 with blood lipids and risk for CAD. Rare LoF variants were defined as protein-truncating variants with minor allele frequency <0.1% in ABCG5 or ABCG8.

RESULTS

In sitosterolemia families, 7 pedigrees harbored causative LoF variants in ABCG5 and 2 pedigrees in ABCG8. Homozygous LoF variants in either ABCG5 or ABCG8 led to marked elevations in sitosterol and LDL-C. Of those sitosterolemia families, heterozygous carriers of ABCG5 LoF variants exhibited increased sitosterol and LDL-C levels compared with noncarriers. Within large-scale CAD case-control cohorts, prevalence of rare LoF variants in ABCG5 and in ABCG8 was ≈0.1% each. ABCG5 heterozygous 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, ABCG8 heterozygous 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 in ABCG5 had significantly increased sitosterol and LDL-C levels and a 2-fold increase in risk of CAD.

The brave new world of genetic testing in the management of the dyslipidaemias

PURPOSE OF REVIEW

With the exception of familial hypercholesterolaemia, the value of genetic testing for managing dyslipidaemias is not established. We review the genetics of major dyslipidaemias in context of clinical practice.

RECENT FINDINGS

Genetic testing for familial hypercholesterolaemia is valuable to enhance diagnostic precision, cascade testing, risk prediction and the use of new medications. Hypertriglyceridaemia may be caused by rare recessive monogenic, or by polygenic, gene variants; genetic testing may be useful in the former, for which antisense therapy targeting apoC-III has been approved. Familial high-density lipoprotein deficiency is caused by specific genetic mutations, but there is no effective therapy. Familial combined hyperlipidaemia (FCHL) is caused by polygenic variants for which there is no specific gene testing panel. Familial dysbetalipoproteinaemia is less frequent and commonly caused by APOE ε2ε2 homozygosity; as with FCHL, it is responsive to lifestyle modifications and statins or/and fibrates. Elevated lipoprotein(a) is a quantitative genetic trait whose value in risk prediction over-rides genetic testing; treatment relies on RNA therapeutics.

SUMMARY

Genetic testing is not at present commonly available for managing dyslipidaemias. Rapidly advancing technology may presage wider use, but its worth will require demonstration of cost-effectiveness and a healthcare workforce trained in genomic medicine.

Orbital involvement of Sitosterolemia

Sitosterolemia is a rare inherited condition in which plant sterols are stored and deposited in the tissues. Described in 1974 by Battacharyya and Connor, it is characterized by tendon and tuberous xanthomas and a propensity to premature coronary atherosclerosis. We present the first reported case of the disease being manifest in the periorbital region. A 44-year-old man presented with a six-month history of swelling below the left eyebrow overlying the orbital rim, but without displacement of the globe. Magnetic resonance imaging identified a soft tissue mass within the orbit, with subsequent biopsy confirming a xanthogranulomatous process consistent with the diagnosis of sitosterolemia. Management of sitosterolemia aims to reduce plasma plant sterol concentrations which subsequently lowers serum cholesterol reducing the xanthomas and atherosclerotic cardiovascular diseases. This report highlights a rare, under-recognised condition (and indeed the first reporting periocular disease), and the potential dangers if misdiagnosed as hypercholesterolemia.

High prevalence of increased sitosterol levels in hypercholesterolemic children suggest underestimation of sitosterolemia incidence

Background

Sitosterolemia is an inherited lipid disorder which presents with elevated serum sitosterol and can result in an increased risk of premature cardiovascular disease. However, sitosterol cannot be accurately measured by routine diagnostic assays, meaning that sitosterolemia diagnosis can often be difficult, especially with many clinical features overlapping with familial hypercholesterolemia. With such complications resulting in increasing reports of misdiagnosis, the prevalence of sitosterolemia is predicted to be much higher than previously reported.

Methods

Gas chromatography-mass spectrometry was utilized to measure sitosterol levels of normocholesterolemic and hypercholesterolemic children. Subsequently, an epidemiologically determined cutoff level of sitosterol was calculated and applied to estimate the prevalence of children with increased sitosterol and identify potential sitosterolemia patients. Massively parallel sequencing was used to confirm the diagnosis in suspected patients.

Results

Samples from 109 normocholesterolemic and 220 hypercholesterolemic were tested for phytosterols. Sitosterol and campesterol levels were significantly increased in hypercholesterolemic children (mean 22.0±45.9 μmol/L for sitosterol and 26.0±32.8 μmol/L for campesterol) compared to normocholesterolemic children (mean 12.1±4.9 μmol/L for sistosterol and 14.8±6.7 μmol/L for campesterol). Via application of a cutoff of 35.9 μmol/L, the prevalence rates for increased and overtly increased sitosterol in hypercholesterolemic children were 6.4% and 1.4% respectively. Furthermore, 3 suspected sitosterolemia patients were identified, with 2 patients receiving molecular confirmation for sitosterolemia diagnosis.

Conclusions

Our findings reaffirm that the prevalence of sitosterolemia is probably much higher than previously reported, which also indicates the significant risk of misdiagnosis of sitosterolemia with familial hypercholesterolemia. Special lipid testing including sitosterol, especially in children with uncontrolled hypercholesterolemia, is recommended in children in order to identify potential sitosterolemia patients that would otherwise be neglected.

Personalized medicine for cardiovascular diseases

Personalized medicine is an emerging concept involving managing the health of patients based on their individual characteristics, including particular genotypes. Cardiovascular diseases are heritable traits, and family history information is useful for risk prediction. As such, determining genetic information (germline genetic mutations) may also be applied to risk prediction. Furthermore, accumulating evidence suggests that genetic background can provide guidance for selecting effective treatments and preventive strategies in individuals with particular genotypes. These concepts may be applicable both to rare Mendelian diseases and to common complex traits. In this review, we define the concept and provide examples of personalized medicine based on human genetics for cardiovascular diseases, including coronary artery disease, arrhythmia, and cardiomyopathies. We also provide a particular focus on Mendelian randomization studies, especially those examining loss-of function genetic variations, for identifying high-risk individuals, as well as signaling pathways that may be useful targets for improving healthy living without cardiovascular events.

The value of physical signs in identifying patients with familial hypercholesterolemia in the era of genetic testing

Familial hypercholesterolemia (FH) is a common, inherited disorder of cholesterol metabolism characterized by very high plasma concentrations of low-density lipoprotein cholesterol. It is crucial to diagnose and treat this disorder early since if left untreated it increases the risk for coronary artery disease (CAD) at least by 10-fold. Although genetic testing for FH, when available and affordable, should ideally be offered to most individuals with clinical phenotype suggestive of FH, it is underutilized in most countries. Therefore, FH diagnosis in the majority of cases is made by combining cholesterol levels and clinical characteristics of the patient leaving the need for genetic testing usually in equivocal cases. The presence of some cutaneous and ocular signs can raise the suspicion or even lead to the diagnosis of FH among usually "healthy" individuals. These physical signs comprise cutaneous lesions such as tendon xanthomas or the less specific xanthelasmata and ocular signs, such as corneal arcus in individuals under the age of 45 years. The presence of these signs should prompt the physician to request lipid tests and use clinical scores to diagnose FH. If the diagnosis of FH is likely, aggressive lipid-lowering therapy should be initiated to reduce the risk of CAD and a cascade screening of family members should also be requested.

It’s time to personalize and optimize lipid-lowering therapy

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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.

Features of Sitosterolemia in Children

Sitosterolemia is a rare lipid metabolism disease with heterogeneous manifestations. Atherosclerosis can occur in children, and therefore, early detection, diagnosis, and treatment of this disease are important. We studied 18 pediatric patients with sitosterolemia who showed a significant increase in plasma lipid levels and analyzed their clinical, biochemical, and genetic characteristics. We recorded the initial serum lipid results and clinical manifestations of the patients. Lipid and plant sterol levels were measured after homozygous or compound heterozygous mutations of ABCG5 or ABCG8 were identified by genetic testing. Plasma plant sterol levels were analyzed by gas chromatography. Fourteen cases of sitosterolemia were examined by ultrasound and echocardiography. The initial total cholesterol and low-density lipoprotein levels of the children were significantly increased, but then markedly decreased after diet control or drug treatment, and even reached normal levels. Carotid atherosclerosis and aortic valve regurgitation were present in three of 14 patients. Serum lipid levels of children with sitosterolemia and xanthomas were notably higher than those without xanthomas. There were no significant differences in clinical manifestations between patients with different genotypes. In conclusion, sitosterolemia should be considered in children with hyperlipidemia who do not present with xanthomas, especially with a significant increase in total cholesterol and low-density lipoprotein levels. There does not appear to be a correlation between clinical phenotype and genotype.

Plant Glycosides and Glycosidases: A Treasure-Trove for Therapeutics

Plants contain numerous glycoconjugates that are metabolized by specific glucosyltransferases and hydrolyzed by specific glycosidases, some also catalyzing synthetic transglycosylation reactions. The documented value of plant-derived glycoconjugates to beneficially modulate metabolism is first addressed. Next, focus is given to glycosidases, the central theme of the review. The therapeutic value of plant glycosidases is discussed as well as the present production in plant platforms of therapeutic human glycosidases used in enzyme replacement therapies. The increasing knowledge on glycosidases, including structure and catalytic mechanism, is described. The novel insights have allowed the design of functionalized highly specific suicide inhibitors of glycosidases. These so-called activity-based probes allow unprecedented visualization of glycosidases cross-species. Here, special attention is paid on the use of such probes in plant science that promote the discovery of novel enzymes and the identification of potential therapeutic inhibitors and chaperones.

A catalog of the pathogenic mutations of LDL receptor gene in Japanese familial hypercholesterolemia

BACKGROUND

Little data exist on the pathogenic mutations of LDL receptor in Japanese familial hypercholesterolemia (FH).

OBJECTIVE

We aimed to catalog the pathogenic mutations of LDL receptor gene in the 2 major Japanese FH-care centers (Kanazawa University and National Cerebral and Cardiovascular Center Research Institute), where genetic testing of FH has been performed centrally on requests from institutes all over Japan during more than past 2 decades.

METHODS

796 FH subjects from 472 families who had nonsynonymous mutations in LDL receptor gene were included in this study. Genetic mutations were analyzed for mutations by Sanger sequencing as well as by multiplex ligation probe dependent amplification technique for large rearrangements. Pathogenic mutations were defined either as 1) protein truncated variants, 2) registered as pathogenic in ClinVar, or Human Gene Mutation Database (HGMD), or meet the criteria of American College of Medical Genetics and Genomics guideline, or 3) CADD score > 10.

RESULTS

We found 138 different mutations. Among them, 132 mutations were considered as pathogenic, including 19 large rearrangement mutations. However, 6 missense mutations were classified as variants of unknown significance. A single mutation accounted for as much as 41% of the FH subjects recruited from Kanazawa University mainly due to founder gene effect, whereas many singleton mutations were found from National Cerebral and Cardiovascular Center Research Institute located in Osaka.

CONCLUSIONS

We provided the largest catalog of pathogenic mutations of LDL receptor gene in Japanese FH. This could aid to determine the pathogenicity of the LDL receptor genetic mutations not only in Japanese but also in other ethnicities.

Beneficial effect of ezetimibe-atorvastatin combination therapy in patients with a mutation in ABCG5 or ABCG8 gene

Background

Use of ezetimibe on top of statin therapy has been shown to be effective to reduce LDL cholesterol level in hypercholesterolemic patients. However, little is known regarding the individual variety of the effectiveness of ezetimibe. We hypothesized that hypercholesterolemic patients with a mutation in ABCG5 or ABCG8 gene exhibit better response to ezetimibe than those without, based on the fact that ezetimibe is hyper-effective for in patients with sitosterolemia caused by ABCG5 or ABCG8 genetic mutations.

Methods

Electronical medical record were reviewed in a total of 321 hypercholesterolemic patients (baseline LDL cholesterol = 192 ± 46 mg/dl) prescribed ezetimibe 10 mg daily on top of atorvastatin 10 mg daily who had undergone genetic analysis of ABCG5 or ABCG8 gene in our institute since 2006 to 2017. Pathogenicity of the variants were determined using standard variant filtering schema, including minor allele frequency, in silico annotation tools. Patients were divided into 2 groups based on the presence of ABCG5 or ABCG8 mutation. We compared the percent reduction of LDL cholesterol as well as the achieved LDL cholesterol levels between these 2 groups.

Results

We found 26 (8%) individuals who exhibit deleterious mutations in ABCG5 or ABCG8 gene. Baseline characteristics under the atorvastatin 10 mg therapy were comparable in age, gender, and LDL cholesterol level between 2 groups. Under these conditions, percent reduction of LDL cholesterol in mutation positive group was significantly larger than that of mutation negative group (28 ± 16% vs. 39 ± 21%, p < 0.05). As a result, the achieved LDL cholesterol level in mutation positive group was significantly lower than that of mutation negative group (87 ± 29 mg/dl vs. 72 ± 26% mg/dl, p < 0.05).

Conclusion

These results suggest that ezetimibe-atorvastatin combination therapy might be more beneficial in hypercholesterolemic patients with a mutation in ABCG5 or ABCG8 gene.

Rare Diseases Related with Lipoprotein Metabolism

Rare diseases are gathering increasing attention in last few years, not only for its effects on innovation scientific research, but also for its propounding influence on common diseases. One of the most famous milestones made by Michael Brown and Joseph Goldstein in metabolism field is the discovery of the defective gene in familial hypercholesterolemia, a rare human genetic disease manifested with extreme high level of serum cholesterol (Goldstein JL, Brown MS, Proc Natl Acad Sci USA 70:2804-2808, 1973; Brown MS, Dana SE, Goldstein JL, J Biol Chem 249:789-796, 1974). Follow-up work including decoding the gene function, mapping-related pathways, and screening therapeutic targets are all based on the primary finding (Goldstein JL, Brown MS Arterioscler Thromb Vasc Biol 29:431-438, 2009). A series of succession win the two brilliant scientists the 1985 Nobel Prize, and bring about statins widely used for lipid management and decreasing cardiovascular disease risks. Translating the clinical extreme phenotypes into laboratory bench work has turned out to be the first important step in the paradigm conducting translational and precise medical research. Here we review the main categories of rare disorders related with lipoprotein metabolism, aiming to strengthen the notion that human rare inheritable genetic diseases would be the window to know ourselves better, to treat someone more efficiently, and to lead a healthy life longer. Few rare diseases related with lipoprotein metabolism were clustered into six sections based on changes in lipid profile, namely, hyper- or hypocholesterolemia, hypo- or hyperalphalipoproteinemia, abetalipoproteinemia, hypobetalipoproteinemia, and sphingolipid metabolism diseases. Each section consists of a brief introduction, followed by a summary of well-known disease-causing genes in one table, and supplemented with one or two diseases as example for detailed description. Here we aimed to raise more attention on rare lipoprotein metabolism diseases, calling for more work from basic research and clinical trials.

Reference Intervals of Serum Non-Cholesterol Sterols by Gender in Healthy Japanese Individuals

AIMS

The present study was conducted to establish a practical method for measuring non-cholesterol sterols and reference intervals of serum levels.

METHODS

Healthy subjects (109 men and 151 women), four patients with sitosterolemia, and 10 heterozygous mutation carriers of ABCG5/ABCG8 genes were investigated. Then, three non-cholesterol sterols (sitosterol, campesterol, and lathosterol) of fasting serum samples were measured via a practical and highly sensitive gas chromatography (GC) method with 0.2 µg/mL as the lower limit of quantification. The coefficient of variation (CV) values for within-run reproducibility were 3.06%, 1.89%, and 1.77% for lathosterol, campesterol, and sitosterol, respectively. The CV values for between-run reproducibility were 2.81%, 2.06%, and 2.10% for lathosterol, campesterol, and sitosterol, respectively.

RESULTS

The serum levels of sitosterol and campesterol were significantly higher in women than in men, whereas the serum levels of lathosterol were significantly higher in men than in women. Because of these gender difference, the determination of reference intervals of the three sterol values was performed by considering gender. The reference intervals of sitosterol, campesterol, and lathosterol were 0.99-3.88, 2.14-7.43, and 0.77-3.60 µg/mL in men and 1.03-4.45, 2.19-8.34, and 0.64-2.78 µg/mL in women, respectively. The serum levels of sitosterol and campesterol were higher in patients with sitosterolemia (94.3±47.3 and 66.3±36.6 µg/mL, respectively) than in healthy subjects.

CONCLUSION

These results demonstrate a practical and highly sensitive GC method to measure non-cholesterol sterol levels and gender-segregated reference intervals of sitosterol, campesterol, and lathosterol in Japanese healthy subjects.

Rare and Deleterious Mutations in ABCG5/ABCG8 Genes Contribute to Mimicking and Worsening of Familial Hypercholesterolemia Phenotype

BACKGROUND

A substantial proportion of patients clinically diagnosed as having familial hypercholesterolemia (FH) do not manifest causative mutation(s) in the FH genes such asLDLR,APOB, andPCSK9. We aimed to evaluate the effect of rare and deleterious mutation(s) inABCG5/ABCG8on hyper-low-density lipoprotein (LDL) cholesterolemia in individuals who meet the clinical criteria for FH.

METHODS AND RESULTS

We compared the LDL cholesterol (LDL-C) values among 487 subjects with FH; the subjects were grouped according to the presence of mutation(s) in FH andABCG5/ABCG8genes. We identified 276 individuals with a deleterious mutation in 1 FH gene (57%, monogenic FH), but found no causative mutations in 156 individuals (32%, mutation-negative). A total of 37 individuals had deleterious mutations inABCG5orABCG8, but not in FH genes (8%,ABCG5/ABCG8mutation carriers). Among these, 3 individuals had sitosterolemia (0.6%) with double mutations. We also identified 18 individuals with deleterious mutations in an FH gene andABCG5orABCG8(4%,ABCG5/ABCG8-oligogenic FH). Subjects without mutations had significantly higher polygenic scores than those in any other groups. LDL-C levels in oligogenic FH subjects were significantly higher than in the monogenic FH subjects. Moreover, sitosterol/lathosterol levels were significantly affected by those mutations.

CONCLUSIONS

The results suggested that rare and deleterious mutations inABCG5/ABCG8contribute substantially to mimicking and exacerbation of the FH phenotype.

Sitosterolemia-10 years observation in two sisters

Familial hypercholesterolemia due to heterozygous low-density lipoprotein-receptor mutations is a common inborn errors of metabolism. Secondary hypercholesterolemia due to a defect in phytosterol metabolism is far less common and may escape diagnosis during the work-up of patients with dyslipidemias. Here we report on two sisters with the rare, autosomal recessive condition, sitosterolemia. This disease is caused by mutations in a defective adenosine triphosphate-binding cassette sterol excretion transporter, leading to highly elevated plant sterol concentrations in tissues and to a wide range of symptoms. After a delayed diagnosis, treatment with a diet low in plant lipids plus ezetimibe to block the absorption of sterols corrected most of the clinical and biochemical signs of the disease. We followed the two patients for over 10 years and report their initial presentation and long-term response to treatment.