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 "ß-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.

Insulin resistance involvement in prevalence of familial dysbetalipoproteinemia in ε2ε2 subjects by Bayesian network modeling.

OBJECTIVE: Familial dysbetalipoproteinemia (FD) or Type III hyperlipoproteinemia is closely associated with the ε2ε2 genotype of the common APOE polymorphism although not all ε2 homozygotes develop FD indicating that additional factors play a role including insulin resistance (IR). The current study was undertaken to explore relationships and influences among factors, especially IR, that might elucidate FD progression pathways. METHODS: Bayesian network (BN) modeling, a probabilistic graphical exploratory data analysis tool that portrays relationships and influences among variables as simple diagrams, was applied to 52 e2e2 subjects. An algorithm based on apolipoprotein and lipid values identified 24 subjects having FD. BN modeling parameters included plasma apoE, HDL cholesterol (HDL-C), apolipoprotein A-I (apoA-I), apolipoprotein A-II (apoA-II), apoA-I/HDL-C ratio, apoA-II/HDL-C ratio, insulin, and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR). RESULTS: Modeling resulted in twenty network graphs. Each graph revealed apoE and the apoA-II/HDL-C ratio as sole determinants of FD prevalence. BN results did not demonstrate a direct role for insulin and HOMA-IR. However, multiple graphs in the set did reveal indirect influence of IR on FD prevalence as conveyed through the apoA-II/HDL-C ratio; while all remaining graphs in the set demonstrated the apoA-II/HDL-C ratio as directly influencing insulin levels and HOMA-IR. For apoE, the other determinant of FD prevalence, results revealed no relationship with IR parameters. CONCLUSIONS: In so far as insulin levels and HOMA-IR are associated with IR in e2e2 subjects, IR may act indirectly in FD progression via the apoA-II/HDL-C ratio; and/or the apoA-II/HDL-C ratio acts directly to promote IR.

Roles of high apolipoprotein E blood levels and HDL in development of familial dysbetalipoproteinemia in ε2ε2 subjects.

OBJECTIVE: Familial dysbetalipoproteinemia (FD) or Type III hyperlipoproteinemia is a mixed hyperlipidemia closely associated with the ε2ε2 genotype of the common APOE polymorphism although not all homozygotes progress to FD. Unlike the polymorphism, few studies explore effects of apolipoprotein E (apoE) blood levels on FD development. Likewise, despite the known apoE2 lipoprotein binding preference for high-density lipoprotein (HDL); little work exists exploring HDL in FD. Accordingly, this study was undertaken to investigate potential roles in FD development for apoE and HDL. Additionally, insulin and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) were investigated in view of reports linking insulin resistance to FD. METHODS: APOE genotyping and levels of apoE, apolipoprotein A-I (apoA-I), apolipoprotein A-II (apoA-II), insulin, HOMA-IR, lipids, and NMR lipoprotein analysis were determined in a cohort of healthy individuals (N=7169). A lipid-based algorithm identified FD in 24 of 52 e2e2 subjects. Logistic regression modeling assessed associations of FD development with measured variables. RESULTS: Univariate models revealed associations with FD significant and positive for apoE, apoA-II/apoA-I, apoA-I/HDL-C, apoA-II/HDL-C, and HOMA-IR. For HDL-C, association was significant but inverse. Results of multivariable models containing apoE with single parameters added revealed statistical significance only for the apoA-II/HDL-C ratio (OR 10.52, 95%CI 1.17-94.79, p=0.036) concurrent with significance for apoE (OR 2.21, 95%CI 1.06-4.65, p=0.035). Interaction was not demonstrated (p=0.36). NMR results revealed for FD versus nonFD subjects generally higher levels of VLDL and small HDL and for IDL few differences. CONCLUSION: High apoE and high apoA-II/HDL-C independently associate with FD development in ε2ε2 individuals.

Autosomal dominant familial dysbetalipoproteinemia: A pathophysiological framework and practical approach to diagnosis and therapy.

Familial dysbetalipoproteinemia (FD) is a genetic disorder of lipoprotein metabolism associated with an increased risk for premature cardiovascular disease. In about 10% of the cases, FD is caused by autosomal dominant mutations in the apolipoprotein E gene (APOE). This review article provides a pathophysiological framework for autosomal dominant FD (ADFD) and discusses diagnostic challenges and therapeutic options. The clinical presentation and diagnostic work-up of ADFD are illustrated by two cases: a male with premature coronary artery disease and a p.K164Q mutation in APOE and a female with mixed hyperlipidemia and a p.R154H mutation in APOE. ADFD is characterized by a fasting and postprandial mixed hyperlipidemia due to increased remnants. Remnants are hepatically cleared by the low-density lipoprotein receptor and the heparan sulfate proteoglycan receptor (HSPG-R). Development of FD is associated with secondary factors like insulin resistance that lead to HSPG-R degradation through sulfatase 2 activation. Diagnostic challenges in ADFD are related to the clinical presentation; lipid phenotype; dominant inheritance pattern; genotyping; and possible misdiagnosis as familial hypercholesterolemia. FD patients respond well to lifestyle changes and to combination therapy with statins and fibrates. To conclude, diagnosing ADFD is important to adequately treat patients and their family members. In patients presenting with mixed hyperlipidemia, (autosomal dominant) FD should be considered as part of the diagnostic work up.

Influence of APOE-2 genotype on the relation between adiposity and plasma lipid levels in patients with vascular disease.

BACKGROUND: Apolipoprotein E (APOE) genotypes are associated with different plasma lipid levels. People with the APO ɛ2 genotype can develop a disorder called dysbetalipoproteinemia (DBL). A possible predisposing factor for DBL is adiposity. We evaluated whether and to what extent the APOE genotype modifies the relation between adiposity and lipids in patients with manifest arterial disease and we looked at possible determinants of DBL in ɛ2 homo- and heterozygote patients. METHODS: This prospective cohort study was performed in 5450 patients with manifest arterial disease from the Secondary Manifestations of ARTerial disease (SMART) study. The APOE genotype was measured in all patients and revealed 58 ɛ2 homozygotes, 663 ɛ2 heterozygotes, 3181 ɛ3 homozygotes and 1548 ɛ4 carriers. The main dependent variable was non-high-density lipoprotein cholesterol (non-HDL-c). The relation between adiposity (including body mass index (BMI), waist circumference (waist), visceral adipose tissue (VAT) and metabolic syndrome (MetS)) and lipids was evaluated with linear regression analyses. Determinants of DBL were evaluated using logistic regression. RESULTS: There was significant effect modification by the APOE genotype on the relation between non-HDL-c and BMI, waist, VAT and MetS. There was an association between BMI and non-HDL-c in ɛ2 homozygotes (ß 0.173, 95% confidence interval (CI) 0.031-0.314, P=0.018) and ɛ4 carriers (ß 0.033, 95% CI 0.020-0.046, P<0.001). In all genotypes, there was an effect of waist, VAT and MetS on non-HDL-c, but these effects were most distinct in ɛ2 homozygotes (waist ß 0.063, 95% CI 0.015-0.110, P=0.011; VAT ß 0.580, 95% CI 0.270-0.889, P=0.001; MetS ß 1.760, 95% CI 0.668-2.852, P=0.002). Determinants of DBL in ɛ2 homo- and heterozygotes were VAT and MetS. CONCLUSION: The APOE genotype modifies the relation between adiposity and plasma lipid levels in patients with vascular disease. The relation between adiposity and lipids is present in all patients, but it is most distinct in ɛ2 homozygote patients. Abdominal fat and MetS are determinants of DBL.

Effects of the absence of apolipoprotein e on lipoproteins, neurocognitive function, and retinal function.

IMPORTANCE: The identification of a patient with a rare form of severe dysbetalipoproteinemia allowed the study of the consequences of total absence of apolipoprotein E (apoE). OBJECTIVES: To discover the molecular basis of this rare disorder and to determine the effects of complete absence of apoE on neurocognitive and visual function and on lipoprotein metabolism. DESIGN, SETTING, AND PARTICIPANTS: Whole-exome sequencing was performed on the patient's DNA. He underwent detailed neurological and visual function testing and lipoprotein analysis. Lipoprotein analysis was also performed in the Cardiovascular Research Institute, University of California, San Francisco, on blood samples from the proband's mother, wife, 2 daughters, and normolipidemic control participants. MAIN OUTCOME MEASURES: Whole-exome sequencing, lipoprotein analysis, and neurocognitive function. RESULTS: The patient was homozygous for an ablative APOE frameshift mutation (c.291del, p.E97fs). No other mutations likely to contribute to the phenotype were discovered, with the possible exception of two, in ABCC2 (p.I670T) and LIPC (p.G137R). Despite complete absence of apoE, he had normal vision, exhibited normal cognitive, neurological, and retinal function, had normal findings on brain magnetic resonance imaging, and had normal cerebrospinal fluid levels of ß-amyloid and tau proteins. He had no significant symptoms of cardiovascular disease except a suggestion of myocardial ischemia on treadmill testing and mild atherosclerosis noted on carotid ultrasonography. He had exceptionally high cholesterol content (760 mg/dL; to convert to millimoles per liter, multiply by 0.0259) and a high cholesterol to triglycerides ratio (1.52) in very low-density lipoproteins with elevated levels of small-diameter high-density lipoproteins, including high levels of prebeta-1 high-density lipoprotein. Intermediate-density lipoproteins, low-density lipoproteins, and very low-density lipoproteins contained elevated apoA-I and apoA-IV levels. The patient's apoC-III and apoC-IV levels were decreased in very low-density lipoproteins. Electron microscopy revealed large lamellar particles having electron-opaque cores attached to electron-lucent zones in intermediate-density and low-density lipoproteins. Low-density lipoprotein particle diameters were distributed bimodally. CONCLUSIONS AND RELEVANCE: Despite a profound effect on lipoprotein metabolism, detailed neurocognitive and retinal studies failed to demonstrate any defects. This suggests that functions of apoE in the brain and eye are not essential or that redundant mechanisms exist whereby its role can be fulfilled. Targeted knockdown of apoE in the central nervous system might be a therapeutic modality in neurodegenerative disorders.

Dietary enrichment of apolipoprotein E-deficient mice with extra virgin olive oil in combination with seal oil inhibits atherogenesis.

BACKGROUND: In this study we investigated the antiatherogenic effect of dietary enrichment of a combination of extra virgin olive oil (EVO) and seal oil on apolipoprotein E-deficient (apoE-/-). METHODS: Six-week-old female and male apoE-/- mice were for 12 weeks fed a lipid rich diet containing 19.5% fat and 1.25% cholesterol without any supplement, with 1% (wt/wt) mixture of extra virgin olive and seal oil (EVO/n-3), or 1% corn oil, respectively. RESULTS: Supplementation with the combination of EVO/n-3 significantly reduced atherosclerotic lesion formation in the aortic arch, thoracoabdominal, and total aorta of female apoE-/-mice. The effect was less pronounced in male mice and significant reduction was only observed in the thoracoabdominal region of the aorta. There were no differences or changes in dietary intake or body weight gain. However, compared to the other groups, plasma levels of triglycerides were reduced in both female and male mice fed the EVO/n-3 mixture. Male mice on both treatments showed reduced plasma cholesterol compared to the control mice after 12 weeks on diet. CONCLUSION: Dietary supplementation of a marine/olive oil combination inhibits atherosclerotic lesion formation in the female apoE-/- mice by antithrombotic, antihypertriglyceridemic, and antioxidant effects.

[Diagnostic image. A woman with orange hand lines]. / Een vrouw met oranje handlijnen.

Incidental cholesterol measurement in a 44-year-old woman revealed 12 mmol/l. She also had orange hand lines and elbow papules, caused by familial dysbetalipoproteinaemia.

Familial dysbetalipoproteinemia: a potentially fatal disorder.

Familial dysbetalipoproteinemia is an inherited disorder in which both cholesterol and triglycerides are elevated in the plasma of the blood, which pre-disposes people to coronary artery disease and peripheral vascular disease. We report two young boys with multiple cutaneous xanthomas and grossly abnormal serum cholesterol and triglycerides. Two of the family members had died of cardiovascular accidents in young age and rest of the family members had deranged lipid profile. Patients were managed with lipid lowering drugs and fat restriction diet. All family members were counseled and advised regular exercise and follow-up.

[Metabolic syndrome and the pancreas. Status of blood circulation in the pancreas in metabolic syndrome in patients with different types of hyperlipoproteinemia ]. / Metabolicheskii sundrom i podzheludochnaia zheleza sostoianien krovoobrashcheniia v podzheludochnoi zheleze pri metabolicheskom sindrome u patsientov s razlichnym tipami giperipoproteinemii.

A study of blood circulation in the pancreas of 42 patients with the metabolic syndrome by the method of intracavitary rheography revealed a drop in the intensity of terminal blood circulation and presence of venous congestion with the activation of venous-arterial shunting. Hemodynamic disorders directly depended on the adiposity degree and patients' age, being evident as signs of a more obvious disorder of terminal blood circulation in patients with HLP of the II and III type.

Dysbetalipoproteinaemia--clinical and pathophysiological features.

OBJECTIVES: Dysbetalipoproteinaemia (type III hyperlipidaemia, broad-beta disease) is a highly atherogenic genetic disorder of lipoprotein metabolism. It presents with a severe mixed hyperlipidaemia in which the ratio of total cholesterol to triglycerides is typically 2:1. There is a high incidence of atherosclerotic complications and severe hypertriglyceridaemia may cause pancreatitis. Highly effective therapy is available and affected families also benefit from genetic counselling. We present a review of our experience with dysbetalipoproteinaemia at the lipid clinic of Groote Schuur Hospital to enhance awareness of this serious condition, for which the index of suspicion should be raised. DESIGN: Retrospective review of case records, 1969-2001. SETTING: Lipid clinic of Groote Schuur Hospital, Cape Town. SUBJECTS: Patients with dysbetalipoproteinaemia diagnosed by the presence of cholesterol-enriched very-low-density lipoproteins (VLDL) and/or dyslipidaemia associated with homozygosity for apolipoprotein E2 or carriers of the apoE2 (Arg145-->Cys) mutation. RESULTS: One hundred and five patients were identified, 55 of whom were male and 50 female. The age at presentation was 48.8 +/- 11.1 years (mean, standard deviation). Total cholesterol was 12.0 +/- 5.5 mmol/l and plasma triglycerides 8.3 +/- 9.8 mmol/l. The ratio (by mass) of cholesterol to triglycerides within VLDL was 0.52 +/- 0.17, while VLDL cholesterol to plasma triglycerides was 0.33 +/- 0.09. Fifty patients were epsilon 2 homozygotes while 22 carried the apoE2 (Arg145-->Cys) mutation. Palmar crease xanthomas occurred in 20% of patients, cutaneous xanthomas in 18%, and tendon xanthomas in 13%. Coronary artery disease was found in 47% of patients and peripheral vascular disease in 20%. Fibrates were the most commonly used hypolipidaemic agents (48%), while 31% of patients received combination therapy with a fibrate and statin. Statin monotherapy was used in 11% of patients and a few patients were treated with niacin or required no drug therapy. The treated cholesterol was 5.7 +/- 2.4 mmol/l, with plasma triglycerides of 2.7 +/- 1.9 mmol/l. CONCLUSIONS: Dysbetalipoproteinaemia is a highly atherogenic disorder and is extremely responsive to therapy. A significant proportion of dysbetalipoproteinaemia locally is caused by the apoE2 (Arg145-->Cys) mutation and is therefore dominantly inherited. This mutation is particularly prevalent in the black community where dysbetalipoproteinaemia may be undiagnosed in many patients. Patients with severe mixed hyperlipidaemia or clinical stigmata of dyslipidaemia should be assessed at a lipid clinic for a specific diagnosis and initiation of therapy.

Lipoprotein lipase compensates for the defective function of apo E variants in vitro by interacting with proteoglycans and lipoprotein receptors.

Lipoprotein lipase (LPL) and apolipoprotein E (apo E) independently enhance binding and uptake of lipoproteins to cells. A coordinate effect of LPL and apo E has been previously described in human hepatozytes where simultaneous addition of both proteins resulted in an additive increase of chylomicron binding and uptake. The role of lipoprotein receptors and proteoglycans in this coordinate effect was now analysed using various cell types and heparinase treatment. To investigate a pathophysiological relevance, the effect of LPL and normal apo E-3 was compared to LPL and four apo E variants, associated with type III hyperlipoproteinemia (HLP). Apo E-3 and LPL increased the binding and uptake of chylomicrons and beta-very low density lipoproteins (VLDL) in an additive way in all cell types analysed, except proteoglycan deficient Chinese hamster ovary (CHO)-cells. Heparinase treatment almost completely abolished the effect of apo E and LPL. Addition of LPL to the apo E variants resulted in significant compensation of their defective function in mediating beta-VLDL binding to low density lipoprotein (LDL)-receptor defective fibroblasts. These findings indicate that the coordinate effect of apo E and LPL is mediated by proteoglycans and lipoprotein receptors, independent of the LDL receptor. LPL may compensate for the defective function of apo E variants by enhancing lipoprotein binding to these receptors. Defects in this mechanism may explain how mutations in the LPL molecule contribute to the manifestation of type III HLP in addition to the presence of a defective apo E.

Dominant expression of type III hyperlipoproteinemia. Pathophysiological insights derived from the structural and kinetic characteristics of ApoE-1 (Lys146-->Glu).

Type III hyperlipoproteinemia is characterized by delayed chylomicron and VLDL remnant catabolism and is associated with homozygosity for the apoE-2 allele. We have identified a kindred in which heterozygosity for an apoE mutant, apoE-1 (Lys146-->Glu), is dominantly associated with the expression of type III hyperlipoproteinemia. DNA sequence analysis of the mutant apoE gene revealed a single-point mutation that resulted in the substitution of glutamic acid (GAG) for lysine (AAG) at residue 146 in the proposed receptor-binding domain of apoE. The pathophysiological effect of this mutation was investigated in vivo by kinetic studies in the patient and six normal subjects, and in vitro by binding studies of apoE-1 (Lys146-->Glu) to LDL receptors on human fibroblasts and to heparin. The kinetic studies revealed that apoE-1 (Lys146-->Glu) was catabolized significantly slower than apoE-3 in normals (P < 0.005). In the proband, the plasma residence times of both apoEs were substantially longer and the production rate of total apoE was about two times higher than in the control subjects. ApoE-1 (Lys146-->Glu) was defective in interacting with LDL receptors, and its ability to displace LDL in an in vitro assay was reduced to 7.7% compared with apoE-3. The affinity of apoE-1 (Lys146-->Glu) to heparin was also markedly reduced compared with both apoE-2 (Arg158-->Cys) and apoE-3. These abnormal in vitro binding characteristics and the altered in vivo metabolism of apoE-1 (Lys146-->Glu) are proposed to result in the functional dominance of this mutation in the affected kindred.

[Physiopathology of primary hyperlipidemias]. / Physiopathologie des hyperlipidémies primitives.

The authors review the present status of our knowledge of the physiopathology of primary hyperlipidaemia. The mechanisms of familial hypercholesterolaemia (reduction in the number of LDL receptors on the surface of hepatic and extrahepatic cells) and of type III hyperlipidaemia (an apo E abnormality associated with another metabolic disorder) are relatively well known. However, the physiopathology of the other hyperlipidaemias remains obscure: polygenic hypercholesterolaemia probably due to a disorder of hepatic LDL receptors; combined familial hyperlipidaemia probably due to abnormally high hepatic apo B synthesis; hyperlipidaemia related to defective chylomicron catabolism in which the lipase system plays a central role and hypertriglyceridaemia caused by an association of genetic and environmental factors.

Dyslipoproteinemia and xanthomatosis.

The cutaneous markers associated with dyslipoproteinemia are reviewed in the context of the current view of lipid and lipoprotein metabolism. The utility of determining the plasma levels of lipoproteins and certain apoproteins in children or adults with xanthomas or xanthelasma is discussed. We hope that early identification and appropriate treatment of such patients will reduce the morbidity and mortality from the two major complications of dyslipoproteinemia--atherosclerotic cardiovascular disease and pancreatitis.

[Primary hyperlipoproteinemias. Clinical, biological and physiopathological aspects]. / Les hyperlipoprotéinémies primaires. Aspects cliniques, biologiques et physiopathologiques.

Primary hyperlipoproteinemias are of great interest as for the physician, as for the searcher, because of their atherogenic properties; on the other hand, a new type of hyperlipoprotenemia, namely hyperalphalipoproteinemia, seems to be a protective factor against clinical complications of atherosclerosis. The clinical, biological and pathophysiologic aspects of these diseases are studied both from author's experience and from the literature data.

Pancreatic alpha and beta cell function in familial dysbetalipoproteinemia.

Resistance to both insulin and glucagon have been considered as possible causes of primary hypertriglyceridemia. In the present research, we have compared insulin and glucagon secretion in five hyperlipidemic patients with familial dysbetalipoproteinemia with five normolipidemic control subjects matched for age, sex and adiposioty. Plasma insulin and glucagon concentrations mesaured during standard oral glucose tolerance and arginine infusion tests were similar in the two groups. Blood glucose fell transiently in the controls, but not in the patients, during the Himsworth test (100 g glucose orally plus 0.05 U insulin per kg body weight intravenously). There were no significant differences in plasma FFA concentrations and responses during all tests between the groups. The percentage reduction in plasma triglyceride concentration during infusion of arginine was similar in the two groups. These results suggest that the patients with familial dysbetalipoproteinemia were slightly less insulin sensitive than the controls. However, primary insensitivity to glucagon or insulin does not appear to be fundamental to the pathogenesis of hyperlipidemia in familial dysbetalipoproteinemia.