Screening for dysbetalipoproteinemia by plasma cholesterol and apolipoprotein B concentrations

Interaction Between Primary Hyperlipidemias and Type 2 Diabetes: Therapeutic Implications

There is a gap of knowledge about the clinical and pathophysiological implications resulting from the interaction between primary hyperlipidemias and type 2 diabetes (T2D). Most of the existing evidence comes from sub-analyses of cohorts; scant information derives from randomized clinical trials. The expected clinical implications of T2D in patients with primary hyperlipidemias is an escalation of their already high cardiovascular risk. There is a need to accurately identify patients with this dual burden and to adequately prescribe lipid-lowering therapies, with the current advancements in newer therapeutic options. This review provides an update on the interactions of primary hyperlipidemias, such as familial combined hyperlipidemia, familial hypercholesterolemia, multifactorial chylomicronemia, lipoprotein (a), and type 2 diabetes.

Evaluation of biochemical algorithms to screen dysbetalipoproteinemia in ε2ε2 and rare APOE variants carriers

OBJECTIVES

Dysbetalipoproteinemia (DBL) is a combined dyslipidemia associated with an increased risk of atherosclerotic cardiovascular diseases mostly occurring in ε2ε2 subjects and infrequently in subjects with rare APOE variants. Several algorithms have been proposed to screen DBL. In this work, we compared the diagnostic performances of nine algorithms including a new one.

METHODS

Patients were divided into 3 groups according to their APOE genotype: ε2ε2 ("ε2ε2", n=49), carriers of rare variants ("APOEmut", n=20) and non-carriers of ε2ε2 nor APOE rare variant ("controls", n=115). The algorithms compared were those from Fredrickson, Sniderman, Boot, Paquette, De Graaf, Sampson, eSampson, Bea and ours, the "Hospices Civils de Lyon (HCL) algorithm". Our gold standard was the presence of a ε2ε2 genotype or of a rare variant associated with triglycerides (TG) >1.7 mmol/L. A replication in the UK Biobank and a robustness analysis were performed by considering only subjects with both TG and low-density lipoprotein-cholesterol (LDLc) >90th percentile.

RESULTS

Total cholesterol (TC)/ApoB and NHDLC/ApoB are the best ratios to suspect DBL. In ε2ε2, according to their likelihood ratios (LR), the most clinically efficient algorithms were the HCL, Sniderman and De Graaf's. In APOEmut, Sniderman's algorithm exhibited the lowest negative LR (0.07) whereas the HCL's exhibited the highest positive LR (29). In both cohorts, the HCL algorithm had the best LR.

CONCLUSIONS

We proposed a powerful algorithm based on ApoB concentration and the routine lipid profile, which performs remarkably well in detecting ε2ε2 or APOE variant-related DBL. Additional studies are needed to further evaluate algorithms performances in DBL carriers of infrequent APOE variants.

Dyslipidaemia in women with polycystic ovary syndrome referred to a teaching hospital in Cape Town, South Africa

The polycystic ovary syndrome (PCOS) imparts health risks including dyslipidaemia, diabetes and cardiovascular disease that are amenable to lifestyle adjustment and/or medication. We describe dyslipidaemia in women referred to a gynaecological endocrine clinic. Clinical data and endocrine and lipoprotein investigations comprising fasting triglyceride (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDLC) and calculated low density lipoprotein cholesterol (LDLC) were studied along with electrophoresis patterns of apolipoprotein B-containing lipoproteins. The 1721 participants comprised black, mixed ancestry, white and Indian individuals (9.8%, 83.2%, 5.8% and 1.2%, respectively). The mean ± standard deviation of the age, body mass index (BMI) and waist/hip ratio were 26.0 ± 5.9 years, 32.3 ± 8.3 kg/m2 and waist/hip ratio 0.88 ± 0.11, respectively. Overweight status (BMI 26-30 kg/m2) and obesity (BMI >30 kg/m2) involved 272 (15.8%) and 1010 (58.7%) individuals, respectively. Morbid obesity (BMI >40 kg/m2) was present in 309 (17.9%) individuals. The TG, TC, HDLC and LDLC concentrations were 1.22 ± 0.86, 4.77 ± 1.02, 1.3 ± 0.36, 2.94 ± 0.94 mmol/L, respectively. LDL hypercholesterolaemia occurred in 753 (43.7%) and exceeded 5 mmol/L in 39 (2.3%) women. Low HDLC (<0.9 mmol/L) affected 122 (7%), hypertriglyceridaemia (>1.7 mmol/L) affected 265 (15.4%) and exceeded 2.5 mmol/L in 91 (5.3%) women. Mixed hyperlipidaemia (TG >1.7, TC >5.0 mmol/L) occurred in 176 (10.2%). Electrophoresis revealed small LDL particles in 79 (4.6%) and dysbetalipoproteinaemia in 13 (0.76%) of the cohort. Small LDL associated with obesity, blood pressure, TG and glucose concentration and higher androgenic state. Many women with PCOS had unfavourable lipoprotein results: mostly moderate changes in TG, HDLC and LDLC. Small LDL is not rare, may aid risk assessment and is best determined directly. Incidental monogenic disorders of lipoprotein metabolism included dysbetalipoproteinaemia, familial hypercholesterolaemia and severe hypertriglyceridaemia. Dyslipidaemia in PCOS requires more careful diagnosis, individualised management and research.

Composition and distribution of lipoproteins after evolocumab in familial dysbetalipoproteinemia: A randomized controlled trial

BACKGROUND

Proprotein convertase subtilisin kexin type 9 (PCSK9) monoclonal antibodies (mAbs) reduce fasting and post fat load cholesterol in non-HDL and intermediate density lipoprotein (IDL) in familial dysbetalipoproteinemia (FD). However, the effect of PCSK9 mAbs on the distribution and composition of atherogenic lipoproteins in patients with FD is unknown.

OBJECTIVE

To evaluate the effect of the PCSK9 mAb evolocumab added to standard lipid-lowering therapy in patients with FD on fasting and post fat load lipoprotein distribution and composition.

METHODS

Randomized placebo-controlled double-blind crossover trial comparing evolocumab (140 mg subcutaneous every 2 weeks) with placebo during two 12-week treatment periods. Patients received an oral fat load at the start and end of each treatment period. Apolipoproteins (apo) were measured with ultracentrifugation, gradient gel electrophoresis, retinyl palmitate and SDS-PAGE.

RESULTS

PCSK9 mAbs significantly reduced particle number of all atherogenic lipoproteins, with a stronger effect on smaller lipoproteins than on larger lipoproteins (e.g. IDL-apoB 49%, 95%confidence interval (CI) 41-59 and very low-density lipoprotein (VLDL)-apoB 33%, 95%CI 16-50). Furthermore, PCSK9 mAbs lowered cholesterol more than triglyceride (TG) in VLDL, IDL and low-density lipoprotein (LDL) (e.g. VLDL-C 48%, 95%CI 29-63%; and VLDL-TG 20%, 95%CI 6.3-41%). PCSK9 mAbs did not affect the post fat load response of chylomicrons.

CONCLUSION

PCSK9 mAbs added to standard lipid-lowering therapy in FD patients significantly reduced lipoprotein particle number, in particular the smaller and more cholesterol-rich lipoproteins (i.e. IDL and LDL). PCSK9 mAbs did not affect chylomicron metabolism. It seems likely that the observed effects are achieved by increased hepatic lipoprotein clearance, but the specific working mechanism of PCSK9 mAbs in FD patients remains to be elucidated.

Severe Hypertriglyceridaemia and Chylomicronaemia Syndrome-Causes, Clinical Presentation, and Therapeutic Options

We have reviewed the genetic basis of chylomicronaemia, the difference between monogenic and polygenic hypertriglyceridaemia, its effects on pancreatic, cardiovascular, and microvascular complications, and current and potential future pharmacotherapies. Severe hypertriglyceridaemia (TG > 10 mmol/L or 1000 mg/dL) is rare with a prevalence of <1%. It has a complex genetic basis. In some individuals, the inheritance of a single rare variant with a large effect size leads to severe hypertriglyceridaemia and fasting chylomicronaemia of monogenic origin, termed as familial chylomicronaemia syndrome (FCS). Alternatively, the accumulation of multiple low-effect variants causes polygenic hypertriglyceridaemia, which increases the tendency to develop fasting chylomicronaemia in presence of acquired factors, termed as multifactorial chylomicronaemia syndrome (MCS). FCS is an autosomal recessive disease characterized by a pathogenic variant of the lipoprotein lipase (LPL) gene or one of its regulators. The risk of pancreatic complications and associated morbidity and mortality are higher in FCS than in MCS. FCS has a more favourable cardiometabolic profile and a low prevalence of atherosclerotic cardiovascular disease (ASCVD) compared to MCS. The cornerstone of the management of severe hypertriglyceridaemia is a very-low-fat diet. FCS does not respond to traditional lipid-lowering therapies. Several novel pharmacotherapeutic agents are in various phases of development. Data on the correlation between genotype and phenotype in FCS are scarce. Further research to investigate the impact of individual gene variants on the natural history of the disease, and its link with ASCVD, microvascular disease, and acute or recurrent pancreatitis, is warranted. Volanesorsen reduces triglyceride concentration and frequency of pancreatitis effectively in patients with FCS and MCS. Several other therapeutic agents are in development. Understanding the natural history of FCS and MCS is necessary to rationalise healthcare resources and decide when to deploy these high-cost low-volume therapeutic agents.

Effect of evolocumab on fasting and post fat load lipids and lipoproteins in familial dysbetalipoproteinemia

BACKGROUND

Familial dysbetalipoproteinemia (FD) is the second most common monogenic lipid disorder (prevalence 1 in 850-3500), characterized by postprandial remnant accumulation and associated with increased cardiovascular disease (CVD) risk. Many FD patients do not achieve non-HDL-C treatment goals, indicating the need for additional lipid-lowering treatment options.

OBJECTIVES

To evaluate the effect of the PCSK9 monoclonal antibody evolocumab added to standard lipid-lowering therapy on fasting and post fat load lipids and lipoproteins in patients with FD.

METHODS

A randomized placebo-controlled double-blind crossover trial comparing evolocumab (140 mg subcutaneous every 2 weeks) with placebo during two 12-week treatment periods. At the start and end of each treatment period patients received an oral fat load. The primary endpoint was the 8-hour post fat load non-HDL-C area under the curve (AUC). Secondary endpoints included fasting and post fat load lipids and lipoproteins.

RESULTS

In total, 28 patients completed the study. Mean age was 62±9 years and 93% had an Ɛ2Ɛ2 genotype. Evolocumab reduced the 8-hour post fat load non-HDL-C AUC with 49% (95%CI 42-55) and apolipoprotein B (apoB) AUC with 47% (95%CI 41-53). Other fasting and absolute post fat load lipids and lipoproteins including triglycerides and remnant-cholesterol were also significantly reduced by evolocumab. However, evolocumab did not have significant effects on the rise above fasting levels that occurred after consumption of the oral fat load.

CONCLUSIONS

Evolocumab added to standard lipid-lowering therapy significantly reduced fasting and absolute post fat load concentrations of non-HDL-C, apoB and other atherogenic lipids and lipoproteins in FD patients. The clinically significant decrease in lipids and lipoproteins can be expected to translate into a reduction in CVD risk in these high-risk patients.

Establishing the relationship between Familial Dysbetalipoproteinemia and genetic variants in the APOE gene

Familial Dysbetalipoproteinemia (FD) is the second most common monogenic dyslipidemia and is associated with a very high cardiovascular risk due to cholesterol‐enriched remnant lipoproteins. FD is usually caused by a recessively inherited variant in the APOE gene (ε2ε2), but variants with dominant inheritance have also been described. The typical dysbetalipoproteinemia phenotype has a delayed onset and requires a metabolic hit. Therefore, the diagnosis of FD should be made by demonstrating both the genotype and dysbetalipoproteinemia phenotype. Next Generation Sequencing is becoming more widely available and can reveal variants in the APOE gene for which the relation with FD is unknown or uncertain. In this article, two approaches are presented to ascertain the relationship of a new variant in the APOE gene with FD. The comprehensive approach consists of determining the pathogenicity of the variant and its causal relationship with FD by confirming a dysbetalipoproteinemia phenotype, and performing in vitro functional tests and, optionally, in vivo postprandial clearance studies. When this is not feasible, a second, pragmatic approach within reach of clinical practice can be followed for individual patients to make decisions on treatment, follow‐up, and family counseling.

Palmar striated xanthomas in clinical practice

Introduction

The aim of this study was to assess the occurrence of palmar striated xanthomas (PSX) in a wide spectrum of lipid disorders ranging from very severe hypercholesterolemia (homozygous familial hypercholesterolemia) to very severe hypertriglyceridemia (chylomicronemia).

Methods

This study involved 3,382 dyslipidemic Caucasian adult patients (1,856 men and 1,526 women) seen at the Chicoutimi Hospital Lipid Clinic (Quebec, Canada), covering a wide range of lipid disorders, from severe hypertriglyceridemia to severe hypercholesterolemia. Categorical variables were compared using the Pearson χ2 statistic, whereas univariate analysis of variance (ANOVA) or nonparametric Kruskal-Wallis were used for continuous variables.

Results

A total of 5.1% (173/3382) of the studied patients presented PSX, a majority of them (67.1%) being women. PSX were observed in 18.8% of patients with dysbetalipoproteinemia and also among 14.1% of hypertriglyceridemic patients with partial lipoprotein lipase deficiency, 3.7% of patients with chylomicronemia and in all of those with homozygous familial hypercholesterolemia. Overall, 10.7% of patients with PSX did not meet dysbetalipoproteinemia diagnosis criteria.

Conclusion

According to our study, the PSX prevalence estimate among patients without dysbetalipoproteinemia would be around 10% and they could be observed in a wide spectrum of lipid disorders associated with recurrent or sustained remnant lipoprotein accumulation.

Dysbetalipoproteinemia: Differentiating Multifactorial Remnant Cholesterol Disease From Genetic ApoE Deficiency

CONTEXT

Dysbetalipoproteinemia (DBL) is characterized by the accumulation of remnant lipoprotein particles and associated with an increased risk of cardiovascular and peripheral vascular disease (PVD). DBL is thought to be mainly caused by the presence of an E2/E2 genotype of the apolipoprotein E (APOE) gene, in addition to environmental factors. However, there exists considerable phenotypic variability among DBL patients.

OBJECTIVE

The objectives were to verify the proportion of DBL subjects, diagnosed using the gold standard Fredrickson criteria, who did not carry E2/E2 and to compare the clinical characteristics of DBL patients with and without E2/E2.

METHODS

A total of 12 432 patients with lipoprotein ultracentrifugation as well as APOE genotype or apoE phenotype data were included in this retrospective study.

RESULTS

Among the 12 432 patients, 4% (n = 524) were positive for Fredrickson criteria (F+), and only 38% (n = 197) of the F+ individuals were E2/E2. The F+ E2/E2 group had significantly higher remnant cholesterol concentration (3.44 vs 1.89 mmol/L) and had higher frequency of DBL-related xanthomas (24% vs 2%) and floating beta (95% vs 11%) than the F+ non-E2/E2 group (P < 0.0001). The F+ E2/E2 group had an independent higher risk of PVD (OR 11.12 [95% CI 1.87-66.05]; P = 0.008) events compared with the F+ non-E2/E2 group.

CONCLUSION

In the largest cohort of DBL worldwide, we demonstrated that the presence of E2/E2 was associated with a more severe DBL phenotype. We suggest that 2 DBL phenotypes should be distinguished: the multifactorial remnant cholesterol disease and the genetic apoE deficiency disease.

The clinical and laboratory investigation of dysbetalipoproteinemia

Familial dysbetalipoproteinemia (type III hyperlipoproteinemia) is a potentially underdiagnosed inherited dyslipidemia associated with greatly increased risk of coronary and peripheral vascular disease. The mixed hyperlipidemia observed in this disorder usually responds well to appropriate medical therapy and lifestyle modification. Although there are characteristic clinical features such as palmar and tuberous xanthomata, associated with dysbetalipoproteinemia, they are not always present, and their absence cannot be used to exclude the disorder. The routine lipid profile cannot distinguish dysbetalipoproteinemia from other causes of mixed hyperlipidemia and so additional investigations are required for confident diagnosis or exclusion. A range of investigations that have been proposed as potential diagnostic tests are discussed in this review, but the definitive biochemical test for dysbetalipoproteinemia is widely considered to be beta quantification. Beta quantification can determine the presence of "β-VLDL" in the supernatant following ultracentrifugation and whether the VLDL cholesterol to triglyceride ratio is elevated. Both features are considered hallmarks of the disease. However, beta quantification and other specialist tests are not widely available and are not high-throughput tests that can practically be applied to all patients with mixed hyperlipidemia. Using apolipoprotein B (as a ratio either to total or non-HDL cholesterol or as part of a multi-step algorithm) as an initial test to select patients for further investigation is a promising approach. Several studies have demonstrated a high degree of diagnostic sensitivity and specificity using these approaches and apolipoprotein B is a relatively low-cost test that is widely available on high-throughput platforms. Genetic testing is also important in the diagnosis, but it should be noted that most individuals with an E₂/₂ genotype do not suffer from remnant hyperlipidemia and around 10% of familial dysbetalipoproteinemia cases are caused by rarer, autosomal dominant mutations in APOE that will only be detected if the gene is fully sequenced. Wider implementation of diagnostic pathways utilizing apo B could lead to more rational use of specialist investigations and more consistent detection of patients with dysbetalipoproteinemia. Without the application of a consistent evidence-based approach to identifying dysbetalipoproteinemia, many cases are likely to remain undiagnosed.

Modern prevalence of dysbetalipoproteinemia (Fredrickson-Levy-Lees type III hyperlipoproteinemia)

INTRODUCTION

Dysbetalipoproteinaemia (HLP3) is a disorder characterized by excess cholesterol-enriched, triglyceride-rich lipoprotein remnants in genetically predisposed individuals that powerfully promote premature cardiovascular disease if untreated. The current prevalence of HLP3 is largely unknown.

MATERIAL AND METHODS

We performed cross-sectional analysis of 128,485 U.S. adults from the Very Large Database of Lipids (VLDbL), using four algorithms to diagnose HLP3 employing three Vertical Auto Profile ultracentrifugation (UC) criteria and a previously described apolipoprotein B (apoB) method. We evaluated 4,926 participants from the 2011-2014 National Health and Nutrition Examination Survey (NHANES) with the apoB method. We examined demographic and lipid characteristics stratified by presence of HLP3 and evaluated lipid characteristics in those with HLP3 phenotype discordance and concordance as determined by apoB and originally defined UC criteria 1.

RESULTS

In U.S. adults in VLDbL and NHANES, a 1.7-2.0% prevalence is observed for HLP3 with the novel apoB method as compared to 0.2-0.8% prevalence in VLDbL via UC criteria 1-3. Participants who were both apoB and UC criteria HLP3 positive had higher remnant particles as well as more elevated triglyceride/apoB and total cholesterol/apoB ratios (all p < 0.001) than those who were apoB method positive and UC criteria 1 negative.

CONCLUSIONS

HLP3 may be more prevalent than historically and clinically appreciated. The apoB method increases HLP3 identification via inclusion of milder phenotypes. Further work should evaluate the clinical implications of HLP3 diagnosis at various lipid algorithm cut-points to evaluate the ideal standard in the modern era.

Inherited metabolic disorders and dyslipidaemia

Monogenic dyslipidaemia is a diverse group of multisystem disorders. Patients may present to various specialities from early childhood to late in adult life, and it usually takes longer before the diagnosis is established. Increased awareness of these disorders among clinicians is imperative for early diagnosis. This best practice review provides an overview of primary dyslipidaemias, highlighting their clinical presentation, relevant biochemical and molecular tests. It also addresses the emerging role of genetics in the early diagnosis and prevention of these disorders.

Non-HDL cholesterol should not generally replace LDL cholesterol in the management of hyperlipidaemia

PURPOSE OF REVIEW

Non-HDL cholesterol was originally conceived as a therapeutic target for statin treatment in hypertriglyceridaemia when apolipoprotein B100 assays were not widely available. Recently non-HDL cholesterol has been recommended to replace LDL cholesterol in the clinical management of dyslipidaemia routinely in general medical practice. This is misguided.

RECENT FINDINGS

Non-HDL cholesterol is heterogeneous, constituting a mixture of triglyceride-rich VLDL, intermediate density lipoprotein and LDL in which small dense LDL is poorly represented and to which VLDL cholesterol contributes increasingly as triglyceride levels rise. This makes it unsuitable as a goal of lipid-lowering treatment or as an arbiter of who should receive such treatment. Results of trials designed to lower LDL cholesterol are not easily translated to non-HDL cholesterol. Fasting is no longer thought essential for screening the general population for raised LDL cholesterol. ApoB100 measurement also does not require fasting even in rarer more extreme lipoprotein disorders encountered in the Lipid Clinic, provides greater precision and specificity and overcomes the problems posed by LDL and non-HDL cholesterol. It is more easily interpreted both in diagnosis and as a therapeutic goal and it includes SD-LDL.

SUMMARY

If we are to discourage use of LDL cholesterol, it should be in favour of apoB100 not non-HDL cholesterol.

Evaluation of the Non-HDL Cholesterol to Apolipoprotein B Ratio as a Screening Test for Dysbetalipoproteinemia

BACKGROUND

Familial dysbetalipoproteinemia is associated with the accumulation of remnant lipoproteins and premature cardiovascular disease. Identification of dysbetalipoproteinemia is important because family members may be affected. Diagnostic testing involves demonstration of β-lipoprotein in the VLDL fraction or characterization of apo E³. These investigations are complex and relatively expensive. The ratios of apo B to total cholesterol and triglycerides have been proposed as screening tests. However, the ratio of non-HDL cholesterol to apo B (NHDLC/apoB) could offer improved performance as the confounding effect of variations in HDL cholesterol is removed.

METHODS

We evaluated NHDLC/apoB as a screening test for dysbetalipoproteinemia, using β-quantification analysis as a reference standard. Data from 1637 patients referred over a 16-year period for β quantification were reviewed retrospectively. In 63 patients, diagnostic criteria for dysbetalipoproteinemia (VLDL cholesterol/triglyceride ratio ≥0.69 and presence of β-VLDL) were fulfilled, and 1574 patients had dysbetalipoproteinemia excluded.

RESULTS

Mean NHDLC/apoB in patients with dysbetalipoproteinemia was 7.3 mmol/g (SD, 1.5 mmol/g) and with dysbetalipoproteinemia excluded was 4.0 mmol/g (SD, 0.5 mmol/g). The optimum cutoff of >4.91 mmol/g achieved a diagnostic sensitivity of 96.8% (95% CI, 89.0-99.6) and specificity of 95.0% (95% CI, 93.8-96.0). NHDLC/apoB offered improved performance compared to total cholesterol/apoB [diagnostic sensitivity 92.1% (95% CI, 82.4-97.4) and specificity 94.5% (95% CI, 93.2-95.6) with a cutoff of >6.55 mmol/g]. NHDL/apoB reference ranges were not sex-dependent, although there was a significant difference between men and women for total cholesterol/apoB.

CONCLUSIONS

NHDLC/apoB offers a simple first-line test for dysbetalipoproteinemia in selecting patients with mixed hyperlipidemia for more complex investigations.

Familial dysbetalipoproteinemia: an underdiagnosed lipid disorder

PURPOSE OF REVIEW

To review pathophysiological, epidemiological and clinical aspects of familial dysbetalipoproteinemia; a model disease for remnant metabolism and remnant-associated cardiovascular risk.

RECENT FINDINGS

Familial dysbetalipoproteinemia is characterized by remnant accumulation caused by impaired remnant clearance, and premature cardiovascular disease. Most familial dysbetalipoproteinemia patients are homozygous for apolipoprotein ε2, which is associated with decreased binding of apolipoprotein E to the LDL receptor. Although familial dysbetalipoproteinemia is an autosomal recessive disease in most cases, 10% is caused by autosomal dominant mutations. Of people with an ε2ε2 genotype 15% develops familial dysbetalipoproteinemia, which is associated with secondary risk factors, such as obesity and insulin resistance, that inhibit remnant clearance by degradation of the heparan sulfate proteoglycan receptor. The prevalence of familial dysbetalipoproteinemia ranges from 0.12 to 0.40% depending on the definition used. Clinical characteristics of familial dysbetalipoproteinemia are xanthomas and mixed hyperlipidemia (high total cholesterol and triglycerides); the primary lipid treatment goal in familial dysbetalipoproteinemia is non-HDL-cholesterol; and treatment consists of dietary therapy and treatment with statin and fibrate combination.

SUMMARY

Familial dysbetalipoproteinemia is a relatively common, though often not diagnosed, lipid disorder characterized by mixed hyperlipidemia, remnant accumulation and premature cardiovascular disease, which should be treated with dietary therapy and statin and fibrate combination.

Hyperlipoproteinemia type 3: the forgotten phenotype

Hyperlipoproteinemia type 3 (HLP3) is caused by impaired removal of triglyceride-rich lipoproteins (TGRL) leading to accumulation of TGRL remnants with abnormal composition. High levels of these remnants, called β-VLDL, promote lipid deposition in tuberous xanthomas, atherosclerosis, premature coronary artery disease, and early myocardial infarction. Recent genetic and molecular studies suggest more genes than previously appreciated may contribute to the expression of HLP3, both through impaired hepatic TGRL processing or removal and increased TGRL production. HLP3 is often highly amenable to appropriate treatment. Nevertheless, most HLP3 probably goes undiagnosed, in part because of lack of awareness of the relatively high prevalence (about 0.2% in women and 0.4-0.5% in men older than 20 years) and largely because of infrequent use of definitive diagnostic methods.

Dysbetalipoproteinemia: Two cases report and a diagnostic algorithm

Dysbetalipoproteinemia is a rare familial dyslipidemia characterized by approximately equally elevated serum cholesterol and triglyceride levels due to accumulated remnant lipoproteins in apolipoprotein E2/E2 homozygotes. It is associated with an increased risk for premature cardiovascular disease. Thus, making a diagnosis of dysbetalipoproteinemia aids in assessing cardiovascular risk correctly and allows for genetic counseling. However, the diagnostic work-up can be challenging. Diagnosis of dysbetalipoproteinemia should be considered in patients mixed dyslipidemia when the apolipoprotein B concentration is relatively low in relation to the total cholesterol concentration or when there is significant disparity between the calculated low density lipoprotein (LDL) and directly measured LDL cholesterol concentrations. Other indices are also informative in the diagnostic process. We present herein two phenotypically different cases (a 44-year-old man with severe hypertriglyceridemia and a 49-year-old woman with mixed dyslipidemia) of genotypically proven familial dysbetalipoproteinemia and a diagnostic algorithm of the disease.

Dysbetalipoproteinaemia: a mixed hyperlipidaemia of remnant lipoproteins due to mutations in apolipoprotein E

Atherosclerosis is strongly associated with dyslipoproteinaemia, and especially with increasing concentrations of low-density lipoprotein and decreasing concentrations of high-density lipoproteins. Its association with increasing concentrations of plasma triglyceride is less clear but, within the mixed hyperlipidaemias, dysbetalipoproteinaemia (Fredrickson type III hyperlipidaemia) has been identified as a very atherogenic entity associated with both premature ischaemic heart disease and peripheral arterial disease. Dysbetalipoproteinaemia is characterized by the accumulation of remnants of chylomicrons and of very low-density lipoproteins. The onset occurs after childhood and usually requires an additional metabolic stressor. In women, onset is typically delayed until menopause. Clinical manifestations may vary from no physical signs to severe cutaneous and tendinous xanthomata, atherosclerosis of coronary and peripheral arteries, and pancreatitis when severe hypertriglyceridaemia is present. Rarely, mutations in apolipoprotein E are associated with lipoprotein glomerulopathy, a condition characterized by progressive proteinuria and renal failure with varying degrees of plasma remnant accumulation. Interestingly, predisposing genetic causes paradoxically result in lower than average cholesterol concentration for most affected persons, but severe dyslipidaemia develops in a minority of patients. The disorder stems from dysfunctional apolipoprotein E in which mutations result in impaired binding to low-density lipoprotein (LDL) receptors and/or heparin sulphate proteoglycans. Apolipoprotein E deficiency may cause a similar phenotype. Making a diagnosis of dysbetalipoproteinaemia aids in assessing cardiovascular risk correctly and allows for genetic counseling. However, the diagnostic work-up may present some challenges. Diagnosis of dysbetalipoproteinaemia should be considered in mixed hyperlipidaemias for which the apolipoprotein B concentration is relatively low in relation to the total cholesterol concentration or when there is significant disparity between the calculated LDL and directly measured LDL cholesterol concentrations. Genetic tests are informative in predicting the risk of developing the disease phenotype and are diagnostic only in the context of hyperlipidaemia. Specialised lipoprotein studies in reference laboratory centres can also assist in diagnosis. Fibrates and statins, or even combination treatment, may be required to control the dyslipidaemia.

Resequencing the APOE gene reveals that rare mutations are not significant contributory factors in the development of type III hyperlipidemia

BACKGROUND

APOE (apolipoprotein E gene) 2/2 genotype and an apolipoprotein B/total cholesterol (ApoB/TC) ratio <0.15 are diagnostic for type III hyperlipidemia. We hypothesized that patients with APOE genotype 2/3 or 2/4 and an ApoB/TC ratio <0.15 may have a mutation in their epsilon 3 or 4 allele, resulting in a type III hyperlipidemia phenotype.

OBJECTIVE

We tested this hypothesis.

METHODS

The DNA sequence of all 4 exons and exon/intron boundaries of the APOE (plus 600 bp upstream of exon 1) of 47 patients with APOE 2/3 and 18 patients with APOE 2/4 genotype and an ApoB/TC ratio <0.15 was determined. As controls the APOE sequence of 53 APOE genotype 2/3 and 20 APOE genotype 2/4 probands with ApoB/TC ratio >0.15 was determined. The sequence analysis was extended to include 47 patients with APOE genotype 3/3, 14 with APOE genotype 3/4, and 3 with APOE genotype 4/4 and an ApoB/TC ratio <0.15. Finally, we determined the sequence of the APOE gene in 145 patients with an ApoB/TC ratio >0.15 and who had triglycerides above the 90th percentile for age and sex.

RESULTS

No deleterious variants in the APOE gene were observed in patients with APOE genotype other than 2/2 and an ApoB/TC ratio <0.15. Only a single probably deleterious variant, K72E, was observed in patients with triglycerides above the 90th percentile.

CONCLUSIONS

Patients with an ApoB/TC ratio <0.15 do not have an increased likelihood of mutation in the APOE gene, and rare variants in the APOE gene are not important in the development of hypertriglyceridemia.

Clinical utility of inflammatory markers and advanced lipoprotein testing: advice from an expert panel of lipid specialists

The National Cholesterol Education Program Adult Treatment Panel guidelines have established low-density lipoprotein cholesterol (LDL-C) treatment goals, and secondary non-high-density lipoprotein (HDL)-C treatment goals for persons with hypertriglyceridemia. The use of lipid-lowering therapies, particularly statins, to achieve these goals has reduced cardiovascular disease (CVD) morbidity and mortality; however, significant residual risk for events remains. This, combined with the rising prevalence of obesity, which has shifted the risk profile of the population toward patients in whom LDL-C is less predictive of CVD events (metabolic syndrome, low HDL-C, elevated triglycerides), has increased interest in the clinical use of inflammatory and lipid biomarker assessments. Furthermore, the cost effectiveness of pharmacological intervention for both the initiation of therapy and the intensification of therapy has been enhanced by the availability of a variety of generic statins. This report describes the consensus view of an expert panel convened by the National Lipid Association to evaluate the use of selected biomarkers [C-reactive protein, lipoprotein-associated phospholipase A(2), apolipoprotein B, LDL particle concentration, lipoprotein(a), and LDL and HDL subfractions] to improve risk assessment, or to adjust therapy. These panel recommendations are intended to provide practical advice to clinicians who wrestle with the challenges of identifying the patients who are most likely to benefit from therapy, or intensification of therapy, to provide the optimum protection from CV risk.

Resequencing the apolipoprotein A5 (APOA5) gene in patients with various forms of hypertriglyceridemia

OBJECTIVE

Genomewide association studies (GWAS), conventional association studies and the characterization of families with ApoA5 deficiency have shown that variation in the apolipoprotein A5 (APOA5) gene is associated with plasma triglyceride levels. The aim of this study was to determine the frequency of rare variants in the APOA5 gene in patients with various forms of hypertriglyceridemia.

METHODS

The DNA sequence of the exons plus exon/intron boundaries of the APOA5 gene of 291 patients with triglycerides above the 95th percentile for age and sex (98 of whom had triglycerides above 875 mg/dl), 111 patients with APOE2/2 genotype of whom 100 had Type III Hyperlipidemia and 108 probands with triglycerides below the 25th percentile for age and sex was determined.

RESULTS

Twenty four variants were detected of which eight have been previously reported. There were nine patients with triglycerides above 875 mg/dl and nine patients with moderately elevated triglycerides who were carriers of at least one deleterious mutation in the APOA5 gene. Of the patients with Type III HLP, three (3%) were carriers of rare variants and there was a single rare variant detected in the group of probands with triglycerides below the 25th percentile for age and sex.

CONCLUSION

Rare mutations in the APOA5 gene are more frequent in patients with elevated triglycerides than in those with Type III HLP.

Rare variants in the lipoprotein lipase (LPL) gene are common in hypertriglyceridemia but rare in Type III hyperlipidemia

OBJECTIVE

Genomewide association studies (GWAS) have shown that variation in the lipoprotein lipase gene (LPL) is associated with plasma triglyceride levels but that common variants account for only 1.25% of the variance. The aim of this study was to determine the frequency of rare variants in the LPL gene in patients with various forms of hypertriglyceridemia.

METHODS

The DNA sequence of the exons plus exon/intron boundaries of the LPL gene of 313 patients with triglycerides above the 95th percentile for age and sex (107 of whom had triglycerides above 875 mg/dl) and 121 patients with Type III hyperlipidemia was determined.

RESULTS

Twenty rare variants were detected of which seven have been previously reported. All of the rare variants were present as heterozygotes. Sixteen were missense mutations, two were short deletion mutants and there were single nonsense and insertion mutations. Fifteen of the missense mutations resulted in an amino acid change. There were 13 patients (12.1%) with triglycerides above 875 mg/dl and 10 patients (4.9%) with moderately elevated triglycerides, who were carriers of at least one rare, non-synonymous mutation in the LPL gene. Of the patients with Type III HLP, two were carriers of rare variants.

CONCLUSION

Rare mutations in the LPL gene are frequent in patients with elevated triglycerides.

Diagnosis and treatment of apolipoprotein B dyslipoproteinemias

Conventionally, atherogenic dyslipidemias have been defined by elevated levels of triglyceride and/or LDL cholesterol. However, cholesterol and triglycerides are not metabolically and physically independent entities. Rather, they are constituents of the atherogenic apolipoprotein B (apoB) particles, which differ in their origin and their metabolic function. Moreover, the risk of vascular disease is not related to the plasma concentration of cholesterol or triglyceride per se, but to the number, composition and size of the apoB particles, within which the cholesterol and triglycerides are contained. After all, the entire apoB particle--rather than individual cholesterol or triglyceride molecules--enters and is trapped within the arterial wall, and this particle initiates and sustains the process that results in atherosclerosis. Accordingly, we suggest a change of name and focus from dyslipidemias to dyslipoproteinemias. Virtually all the atherogenic apoB dyslipoproteinemias can be specifically identified on the basis of plasma levels of cholesterol, triglyceride and apoB. Not only does this enable an accurate diagnosis in the individual, but the major familial dyslipoproteinemias can be identified as well. Here, we review the diagnostic algorithm for apoB dyslipoproteinemias and provide, for the first time, a treatment plan on the basis of a reduction of atherogenic lipoprotein particles rather than plasma lipids.

Pregnancy-induced hyperlipoproteinemia: review of the literature

It is well known that with the effect of hormonal changes during pregnancy, plasma lipid levels increase. Expected elevations for triglyceride and cholesterol levels during a normal gestational period usually do not exceed 332 mg/dL and 337 mg/dL, respectively (corresponding 95th percentile values). However, elevations over the 95th percentile values can be observed during pregnancy, and patients with levels over these expected adaptation levels can be divided into 2 groups: (1) supraphysiologic hyperlipoproteinemia during pregnancy and (2) extreme hyperlipoproteinemia limited to gestational period (triglyceride level >1000 mg/dL). Regarding the first group, some of these patients may develop hyperlipoproteinemia in their future life. What percentage of these women will translate into hyperlipoproteinemia later in life and how efficiently these women can be screened during pregnancy is an enigma. The underlying disorders in the second group of patients at least include dysbetalipoproteinemia, partial lipoprotein lipase deficiency, and apoprotein E3/3 genotype. Pregnancy had been reported to induce severe hyperlipoproteinemia that is limited to gestational period in these disorders. Dysbetalipoproteinemia, partial lipoprotein lipase deficiency, and apoprotein E3/3 genotype probably bring risks and implications to the future life of the carrying individuals although the true extent of the risks is yet to be defined. When disorders unique to gestational period such as gestational diabetes are considered, pregnancy may be accepted as an opportunity to identify women under risk of cardiovascular morbidity and mortality.

The D9N, N291S and S447X variants in the lipoprotein lipase (LPL) gene are not associated with Type III hyperlipidemia

BACKGROUND

Type III hyperlipidemia (Type III HLP) is associated with homozygosity for the epsilon2 allele of the APOE gene. However only about 10% of epsilon2 homozygotes develop Type III HLP and it is assumed that additional genetic and/or environmental factors are required for its development. Common variants in the LPL gene have been proposed as likely genetic co-factors.

METHODS

The frequency of the LPL SNPs D9N, N291S and S447X in 100 patients with hyperlipidemia and APOE2/2 genotype has been determined and compared to that in healthy blood donors and patients with hyperlipidemia.

RESULTS

There were no statistically significant difference in the frequencies of the variants between APOE2/2 patients and controls.

CONCLUSION

It is unlikely that the D9N, N291S or S447X variants in the LPL gene play an important role in the development of Type III HLP.