The Inherited Hypercholesterolemias

Opportunistic Detection of Phytosterolemia During Genetic Testing for FH: Case Series and Contextual Review

BACKGROUND

Homozygous phytosterolemia is a rare autosomal recessive disorder that leads to severely elevated plasma levels of plant phytosterols, causing an increased risk of coronary artery disease (CAD) and mimicking the clinical presentation of familial hypercholesterolemia (FH). Integration of the genetic variants for homozygous phytosterolemia into the genetic panel for FH in clinical practice likely increases the detection of milder genetic forms of phytosterolemia, the implications of which in clinical practice, including cascade testing, remain unclear.

RESULTS

We report 3 families with pathogenic loss-of-function variants in ABCG5 and/or ABCG8, in which probands were identified incidentally when genetically testing them for FH. The proband of the first family was a 35-year-old man with a homozygous ABCG5 loss-of-function variant (c.1336C > T, p.Arg446*) causing severe phytosterolemia and premature CAD on cardiac imaging; his younger brother was heterozygous for the same variant with mildly elevated phytosterol levels. The second family included 2 sisters (aged 31 and 29 years) with digenic variants in ABCG5 (c.1336C > T, p.Arg446*) and ABCG8 (c.1269G > T, p.Glu423Asp with uncertain significance) with moderately elevated plasma phytosterol levels and premature CAD on cardiac imaging. The third family is a 68-year-old man and his 44-year-old daughter who were both heterozygous for a pathogenic ABCG5 variant (c.1166G > A, p.Arg389His) that had mild phytosterolemia and CAD on cardiac imaging. Treatment with ezetimibe alone or in combination with colesevelam reduced elevated plasma sitosterol and campesterol concentrations by 30% to 80%.

CONCLUSION

Phytosterolemia is specific genetic disorder that can mimic FH, cause premature atherosclerosis, and require specific pharmacotherapy. Cascade testing for pathogenic ABCG5/G8 variants can lead to earlier detection and treatment of affected family members.

Phytosterols and phytostanols in context: From physiology and pathophysiology to food supplementation and clinical practice

Phytosterols and phytostanols are two classes of sterol derivatives naturally synthesised in plants, but not in humans. Structurally, phytosterols and phytostanols have a sterane ring in common, but phytostanols do not have a double bond between carbons 5 and 6. The therapeutic potential of phytosterols and phytostanols supplementation in cholesterol reduction is the main reason for its wide usage in an expansive food matrix, including milk, yoghurt, margarine, mayonnaise, chocolate, tartare, chips, esterification with omega-3, and recently, as a successful nutraceutical among athletes is its fortification with whey protein. The heterogeneous effect of phytosterols and phytostanols in cholesterol lowering appears to be related to whether the individuals' inherent physiologic tendencies to "hyper-synthesise" cholesterol in the liver or "hyperabsorb" cholesterol via the small intestine. Individuals who are 'hypersynthesizers" of cholesterol tend to have a good reduction in plasma low-density lipoprotein cholesterol (LDLc) in response to statin therapy. Conversely, "hyper-absorbers" of cholesterol show a greater LDLc lowering in response to phytosterols or phytostanols. The ratios of cholestanol to cholesterol and lathosterol to cholesterol are good biomarkers of intestinal absorption of cholesterol and hepatic cholesterol synthesis. Animal data and human observational data suggest that phytosterols and phytostanols may have anti-atherosclerotic activities, e.g. reduction of the formation of nitric oxide, antagonism to the formation of LDL aggregates and plaque formation. The absence of cardiovascular outcome trials using phytosterol or phytostanol supplementation, makes it difficult to confirm a wider use in clinical practice, especially with the rapidly expanding list of effective and safe lipid-lowering medications.

Exploring Disparities in Atherosclerosis Comorbidity with Aortic Aneurysm

Aortic aneurysm (AA) and atherosclerosis (AS) of various vascular beds are asymptomatic for a long time and are relatively common pathological conditions that lead to life-threatening and disabling complications. In this review, we discuss the current understanding of the high variation in direct and inverse comorbidity of AA and AS as presented in scientific publications. Estimates of AA and AS comorbidity depend on several factors, such as the location of AA (ascending or descending thoracic aorta or abdominal aorta), familial or sporadic cases of AA, syndromic forms of AA, and/or aortic valve pathology (bicuspid aortic valve [BAV]). To identify the causes of the comorbidity of AA and AS, it is important to consider and characterise many factors in detail. These factors include clinical characteristics of the patients included in a study (age, sex) and risk factors (mainly the presence of monogenic forms and BAV, hypertension, hypercholesterolaemia, diabetes mellitus, and cigarette smoking). Additionally, it is essential to consider characteristics of the disease course and the nature of multimorbidity and to take into account pathologies not only of the cardiovascular system but also of other organ systems, with special attention to metabolic and endocrine disorders.

Improving cholesterol management in high-risk primary prevention patients: An evidence-based case series

The National Lipid Association (NLA) is currently conducting a study to improve the uptake of evidence-based guidelines into clinical practice through the deployment of case-based online learning modules to participating health systems nationwide. The Translating Evidence-based Approaches into optimal Care of High-risk atherosclerotic cardiovascular disease patients (TEACH-ASCVD) will evaluate the impact of electronic learning modules on clinician practices related to ASCVD management. In the design phase of TEACH-ASCVD, expert lipidologists created a series of 7 cases informed by recent guidelines intended to provide common clinical scenarios that evaluate participant knowledge of evidence-based practices for high-risk ASCVD and familial hypercholesterolemia. In this manuscript, we present 4 primary prevention-focused cases in high-risk patients and discuss pertinent clinical teaching points. These cases are intended for individuals with clinical lipidology training. We encourage lipidologists to disseminate this manuscript and utilize these cases as a teaching tool for nonlipid specialists to hone their knowledge of common clinical ASCVD risk management scenarios.

The impact of overweight on lipid phenotype in different forms of dyslipidemia: a retrospective cohort study

PURPOSE

Dyslipidemia plays a pivotal role in increasing cardiovascular risk. In clinical practice the misleading association between altered lipid profile and obesity is common, therefore genetically inherited dyslipidemias may not completely be addressed among patients with overweight. Thus, we aim to investigate the influence of overweight and obesity on the lipid phenotype in a cohort of patients with different forms of dyslipidemia.

METHODS

A retrospective analysis was conducted on patients with dyslipidemia from 2015 to 2022. Patients were stratified in familial hypercholesterolemia (FH), familial combined hyperlipidemia (FCHL), non-familial hyperlipidemia or polygenic hypercholesterolemia (PH). Clinical characteristics and lipid profile were evaluated.

RESULTS

Of the total of 798 patients, 361 were affected by non-familial hyperlipidemia (45.2%), while FCHL, FH and PH was described in 19.9%, 14.0% and 20.9% of patients, respectively. Overweight prevalence was higher in FCHL and non-familial hyperlipidemia patients than FH and PH patients. Subjects with overweight and obesity were independently associated with lower levels of high-density lipoprotein cholesterol (HDL-C) compared to patients with normal weight (52.4 and 46.0 vs 58.1, respectively; p < 0.0001); levels of triglycerides (TG) and non-HDL-C were higher in patients with overweight and obesity than patients with normal weight (257.3 and 290.9 vs 194.8, and 221.5 and 219.6 vs 210.1, p < 0.0001 and p = 0.01, respectively), while no differences were observed between patients with overweight and obesity.

CONCLUSION

While dyslipidemias can be influenced by various factors, an important determinant may lie in genetics, frequently acting as an underlying cause of altered lipid profiles, even in cases of overweight conditions.

Lipoprotein(a) distribution in hospitalised Asian patients with ischaemic heart disease

BACKGROUND

Elevated lipoprotein(a) [Lp(a)] is a common hyperlipidaemic condition with strong genetic predisposition and is independently associated with ischaemic heart disease (IHD). A Mendelian randomisation study has suggested that elevated Lp(a) is likely to confer similar causal risks as heterozygous familial hypercholesterolemia for premature IHD. We aimed to characterise the clinical profiles of admitted patients with IHD with at least one Lp(a) measurement. We also investigated whether elevated Lp(a) concentration was associated with premature onset of IHD.

METHODS

This is a descriptive, non-interventional, retrospective study with data from a single tertiary hospital IHD Lp(a) cohort in Singapore, which consecutively recruited 521 patients with IHD admitted to the hospital.

RESULTS

A total of 82.2% were men, 46.6% had newly diagnosed IHD and 10% had premature IHD. The median Lp(a) levels was 35.2 nmol/L. 70.8% of patients had normal Lp(a) concentrations (<70 nmol/L), 13.4% of people with Lp(a) ⩾ 70 to <120 nmol/L and 15.7% of patients with Lp(a) ⩾ 120 nmol/L. Lp(a) distribution was positively skewed to the right for all ethnicities. Patients of Indian ethnicity and of female gender had higher levels of Lp(a) compared with other ethnicities and gender, respectively. Multivariable regression analysis identified Lp(a) ⩾ 155 mmol/L to be associated with development of premature IHD (OR = 2.90, 95% CI: 1.26-6.67, p = 0.012).

CONCLUSION

There exist differences in Lp(a) distribution across ethnicities and gender. The subgroup analysis suggests that Lp(a) ⩾ 155 mmol/L was associated with premature onset of IHD.

Cholesterol Screening in Children: Is a Universal Approach Working?

PURPOSE OF REVIEW

Ample evidence supports that an individual's lifetime risk of atherosclerotic cardiovascular disease correlates to long-term, cumulative exposure to circulating cholesterol levels, beginning in childhood. Selective screening strategies based on family history fail to identify many children with hypercholesterolemia. Universal cholesterol screening in childhood is a worthwhile goal. However, cholesterol screening rates through childhood remain low.

RECENT FINDINGS

Mounting evidence clarifies the barriers to cholesterol screening in children. Specific strategies to foster universal screening in childhood have been proposed.

SUMMARY

We present an overview of the present state of childhood cholesterol screening, summarizing historical and contemporary guidelines and collating evidence of low adherence to current guidelines. We contend that novel approaches to universal cholesterol screening in childhood are warranted, and we present potential opportunities for improvement. We call for new and universal pediatric cholesterol screening guidelines.

Xenosterolemia in clinical practice: what is in a name?

PURPOSE OF REVIEW

The aim of this study was to assess the potential value of the measurement of plasma xenosterols (or phytosterols) concentrations in clinical practice.

RECENT FINDINGS

Recent genetic studies suggest that individuals with elevated plasma phytosterol concentrations due to monogenic and polygenic variants are at an increased risk of coronary artery disease. This supports early observations that elevated plasma phytosterol concentrations are per se atherogenic.

SUMMARY

Measurement of plasma phytosterols can identify individuals with xenosterolemia (or phytosterolemia). This may be clinically useful in four ways: Establishing a diagnosis and informing management of patients with homozygous phytosterolemia; Providing a comprehensive differential diagnosis for familial hypercholesterolemia; Providing an index of cholesterol absorption that may inform personalized pharmacotherapy; and Informing more precise assessment of risk of cardiovascular disease.

Low-carbohydrate diets in type 1 diabetes: balancing benefits and risks

PURPOSE OF REVIEW

Interest in the use of calorie restriction with low-carbohydrate diets for patients with type 1 diabetes appears to be increasing despite physicians' discomfort about its longer term outcomes. A divergence in opinion regarding the balance of benefits and safety may lead to patient disengagement from conventional medical supervision. This review describes the current evidence regarding the benefits and risks of these diets and suggests a way forward to addressing this potential misalignment between the aims of patients and their physicians.

RECENT FINDINGS

Benefits on glycaemia are observed in many studies, with improved HbA1c, time within target range and reduced glycaemic variability. A characteristic lipid profile with high LDL cholesterol is observed in many patients, but association with future cardiovascular events is undefined. A negative impact on growth has been identified in the paediatric population, and impact on mental health and disordered eating is of theoretical concern, without measurement in clinical studies.

SUMMARY

Patients will continue to trial and, with immediate glycaemic benefits, potentially remain on lower carbohydrate diets irrespective of concern by treating physicians about potential longer term risks. A supportive multidisciplinary approach with greater nutritional supervision and more research is required, to allow these patients to achieve their desired glycaemic outcomes without compromising longer term safety.

The clinical utility of polygenic risk scores for combined hyperlipidemia

PURPOSE OF REVIEW

Combined hyperlipidemia is the most common lipid disorder and is strongly polygenic. Given its prevalence and associated risk for atherosclerotic cardiovascular disease, this review describes the potential for utilizing polygenic risk scores for risk prediction and management of combined hyperlipidemia.

RECENT FINDINGS

Different diagnostic criteria have led to inconsistent prevalence estimates and missed diagnoses. Given that individuals with combined hyperlipidemia have risk estimates for incident coronary artery disease similar to individuals with familial hypercholesterolemia, early identification and therapeutic management of those affected is crucial. With diagnostic criteria including traits such apolipoprotein B, low-density lipoprotein cholesterol, and triglyceride, polygenic risk scores for these traits strongly associate with combined hyperlipidemia and could be used in combination for clinical risk prediction models and developing specific treatment plans for patients.

SUMMARY

Polygenic risk scores are effective tools in risk prediction of combined hyperlipidemia, can provide insight into disease pathophysiology, and may be useful in managing and guiding treatment plans for patients. However, efforts to ensure equitable polygenic risk score performance across different genetic ancestry groups is necessary before clinical implementation in order to prevent the exacerbation of racial disparities in the clinic.

The Management of Hypercholesterolemia in Patients with Neuromuscular Disorder

PURPOSE OF REVIEW

We describe and discuss the safety of statins and non-statin drugs in neuromuscular disorders (NMDs). We also propose a pragmatic model of care for the management of such cases.

RECENT FINDINGS

Patients with both NMD and hypercholesterolemia may be particularly disadvantaged owing to the toxic effects of cholesterol-lowering therapy and the inability to take medication. Specifically, the management of hypercholesterolemia in patients with NMD is complicated by the increased risk of statin-related myotoxicity and concerns that statins may aggravate or possibly induce the onset of a specific NMD. The most severe form of statin-related myotoxicity is immune-mediated necrotizing myopathy. Management of hypercholesterolemia in patients with NMDs include treating modifiable factors, consideration of toxicity risk of statin, use of non-statin lipid lowering agents, noting possible drug interactions, and careful monitoring.