A functional polymorphism in the promoter region of the microsomal triglyceride transfer protein (MTP -493G/T) influences lipoprotein phenotype in familial hypercholesterolemia

Effects of Dicyclohexyl Phthalate Exposure on PXR Activation and Lipid Homeostasis in Mice

BACKGROUND

Exposure to plastic-associated endocrine disrupting chemicals (EDCs) has been associated with an increased risk of cardiovascular disease (CVD) in humans. However, the underlying mechanisms for this association are unclear. Many EDCs have been shown to function as ligands of the nuclear receptor pregnane X receptor (PXR), which functions as xenobiotic sensor but also has pro-atherogenic effects in vivo.

OBJECTIVE

We sought to investigate the contribution of PXR to the adverse effects dicyclohexyl phthalate (DCHP), a widely used phthalate plasticizer, on lipid homeostasis and CVD risk factors.

METHODS

Cell-based assays, primary organoid cultures, and PXR conditional knockout and PXR-humanized mouse models were used to investigate the impact of DCHP exposure on PXR activation and lipid homeostasis in vitro and in vivo. Targeted lipidomics were performed to measure circulating ceramides, novel predictors for CVD.

RESULTS

DCHP was identified as a potent PXR-selective agonist that led to higher plasma cholesterol levels in wild-type mice. DCHP was then demonstrated to activate intestinal PXR to elicit hyperlipidemia by using tissue-specific PXR-deficient mice. Interestingly, DCHP exposure also led to higher circulating ceramides in a PXR-dependent manner. DCHP-mediated PXR activation stimulated the expression of intestinal genes mediating lipogenesis and ceramide synthesis. Given that PXR exhibits considerable species-specific differences in receptor pharmacology, PXR-humanized mice were also used to replicate these findings.

DISCUSSION

Although the adverse health effects of several well-known phthalates have attracted considerable attention, little is known about the potential impact of DCHP on human health. Our studies demonstrate that DCHP activated PXR to induce hypercholesterolemia and ceramide production in mice. These results indicate a potentially important role of PXR in contributing to the deleterious effects of plastic-associated EDCs on cardiovascular health in humans. Testing PXR activation should be considered for risk assessment of phthalates and other EDCs. https://doi.org/10.1289/EHP9262.

Pharmacogenomics Variability of Lipid-Lowering Therapies in Familial Hypercholesterolemia

The exponential expansion of genomic data coupled with the lack of appropriate clinical categorization of the variants is posing a major challenge to conventional medications for many common and rare diseases. To narrow this gap and achieve the goals of personalized medicine, a collaborative effort should be made to characterize the genomic variants functionally and clinically with a massive global genomic sequencing of "healthy" subjects from several ethnicities. Familial-based clustered diseases with homogenous genetic backgrounds are amongst the most beneficial tools to help address this challenge. This review will discuss the diagnosis, management, and clinical monitoring of familial hypercholesterolemia patients from a wide angle to cover both the genetic mutations underlying the phenotype, and the pharmacogenomic traits unveiled by the conventional and novel therapeutic approaches. Achieving a drug-related interactive genomic map will potentially benefit populations at risk across the globe who suffer from dyslipidemia.

Efficacy of Polyphenols in the Management of Dyslipidemia: A Focus on Clinical Studies

Polyphenols (PLPs), phytochemicals found in a wide range of plant-based foods, have gained extensive attention in view of their antioxidant, anti-inflammatory, immunomodulatory and several additional beneficial activities. The health-promoting effects noted in animal models of various non-communicable diseases explain the growing interest in these molecules. In particular, in vitro and animal studies reported an attenuation of lipid disorders in response to PLPs. However, despite promising preclinical investigations, the effectiveness of PLPs in human dyslipidemia (DLP) is less clear and necessitates revision of available literature. Therefore, the present review analyzes the role of PLPs in managing clinical DLP, notably by dissecting their potential in ameliorating lipid/lipoprotein metabolism and alleviating hyperlipidemia, both postprandially and in long-term interventions. To this end, PubMed was used for article search. The search terms included polyphenols, lipids, triglycerides, cholesterol, LDL-cholesterol and /or HDL-cholesterol. The critical examination of the trials published to date illustrates certain benefits on blood lipids along with co-morbidities in participant’s health status. However, inconsistent results document significant research gaps, potentially owing to study heterogeneity and lack of rigor in establishing PLP bioavailability during supplementation. This underlines the need for further efforts in order to elucidate and support a potential role of PLPs in fighting DLP.

Triglyceride metabolism and angiopoietin-like proteins in lipoprotein lipase regulation

Hypertriglyceridemia is a risk factor for a series of diseases, such as cardiovascular disease (CVD), diabetes and nonalcoholic fatty liver disease (NAFLD). Angiopoietin-like proteins (ANGPTLs) family, especially ANGPTL3, ANGPTL4 and ANGPTL8, which regulate lipoprotein lipase (LPL) activity, play pivotal roles in triglyceride (TG) metabolism and related diseases/complications. There are many transcriptional and post-transcriptional factors that participate in physiological and pathological regulation of ANGPTLs to affect triglyceride metabolism. This review is intended to focus on the similarity and difference in the expression, structural features, regulation profile of the three ANGPTLs and inhibitory models for LPL. Description of the regulatory factors of ANGPTLs and the properties in regulating the lipid metabolism involved in the underlying mechanisms in pathological effects on diseases will provide potential therapeutic approaches for the treatment of dyslipidemia related diseases.

The atypical antipsychotic quetiapine induces hyperlipidemia by activating intestinal PXR signaling

Quetiapine, one of the most prescribed atypical antipsychotics, has been associated with hyperlipidemia and an increased risk for cardiovascular disease in patients, but the underlying mechanisms remain unknown. Here, we identified quetiapine as a potent and selective agonist for pregnane X receptor (PXR), a key nuclear receptor that regulates xenobiotic metabolism in the liver and intestine. Recent studies have indicated that PXR also plays an important role in lipid homeostasis. We generated potentially novel tissue-specific PXR-KO mice and demonstrated that quetiapine induced hyperlipidemia by activating intestinal PXR signaling. Quetiapine-mediated PXR activation stimulated the intestinal expression of cholesterol transporter Niemann-Pick C1-Like 1 (NPC1L1) and microsomal triglyceride transfer protein (MTP), leading to increased intestinal lipid absorption. While NPC1L1 is a known PXR target gene, we identified a DR-1-type PXR-response element in the MTP promoter and established MTP as a potentially novel transcriptional target of PXR. Quetiapine's effects on PXR-mediated gene expression and cholesterol uptake were also confirmed in cultured murine enteroids and human intestinal cells. Our findings suggest a potential role of PXR in mediating adverse effects of quetiapine in humans and provide mechanistic insights for certain atypical antipsychotic-associated dyslipidemia.

Association of L-FABP T94A and MTP I128T polymorphisms with hyperlipidemia in Chinese subjects

The purpose of this study was to evaluate the relation between the L-FABP T94A and MTP I128T polymorphisms and hyperlipidemia in Chinese subjects. We recruited 390 volunteers: 201 hyperlipidemic and 189 healthy volunteers. The L-FABP T94A and MTP I128T polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Anthropometry, lipid profile, and liver function of the subjects were determined. We observed that male carriers of the L-FABP A94 allele had significantly higher body weight (P = 0.012), higher body mass index (BMI) (P = 0.014), and higher plasma triacylglycerol levels (TAG) (P = 0.033) and lower ratios of high-density lipoprotein cholesterol (HDL-C) to total cholesterol (TC) (P = 0.008) than T94 homozygotes. The MTP T128 allele was associated with significantly lower serum TC (P < 0.001) and low-density lipoprotein cholesterol (LDL-C) (P < 0.001) levels in males. There was a direct correlation between the MTP T128 allele and a decreased risk of hyperlipidemia after adjusting for body mass index (OR = 0.327, 95 % CI: 0.178-0.600, P < 0.001). In conclusion, both the MTP I128T and the L-FABP T94A polymorphisms can affect serum lipid levels in the Chinese population. The MTP T128 allele offers protection against hyperlipidemia in the Chinese population.

Association of polymorphisms of genes involved in lipid metabolism with blood pressure and lipid values in mexican hypertensive individuals

Hypertension and dyslipidemia exhibit an important clinical relationship because an increase in blood lipids yields an increase in blood pressure (BP). We analyzed the associations of seven polymorphisms of genes involved in lipid metabolism (APOA5 rs3135506, APOB rs1042031, FABP2 rs1799883, LDLR rs5925, LIPC rs1800588, LPL rs328, and MTTP rs1800591) with blood pressure and lipid values in Mexican hypertensive (HT) patients. A total of 160 HT patients and 160 normotensive individuals were included. Genotyping was performed through PCR-RFLP, PCR-AIRS, and sequencing. The results showed significant associations in the HT group and HT subgroups classified as normolipemic and hyperlipemic. The alleles FABP2 p.55T, LIPC −514T, and MTTP −493T were associated with elevated systolic BP. Five alleles were associated with lipids. LPL p.474X and FABP2 p.55T were associated with decreased total cholesterol and LDL-C, respectively; APOA5 p.19W with increased HDL-C; APOA5 p.19W and FABP2 p.55T with increased triglycerides; and APOB p.4181K and LDLR c.1959T with decreased triglycerides. The APOB p.E4181K polymorphism increases the risk for HT (OR = 1.85, 95% CI: 1.17–2.93; P = 0.001) under the dominant model. These findings indicate that polymorphisms of lipid metabolism genes modify systolic BP and lipid levels and may be important in the development of essential hypertension and dyslipidemia in Mexican HT patients.

MTTP polymorphisms and susceptibility to non-alcoholic fatty liver disease in a Han Chinese population

BACKGROUND

The microsomal triglyceride transfer protein (MTP) is required for the assembly and secretion of apolipoprotein B (ApoB)-containing lipoproteins from the liver and intestine. Previous studies showed that functional polymorphisms in the MTTP gene correspond to lower LDL levels and protect against other traits of the metabolic syndrome.

AIMS

Here, we aimed to investigate whether MTTP single nucleotide polymorphisms (SNPs) and their predicted haplotypes of linkage disequilibrium blocks contribute to non-alcoholic fatty liver disease (NAFLD) susceptibility in a Han Chinese population.

METHODS

Seven tag SNPs in the MTTP gene were selected and genotyped in a frequency-matched case-control study in a population from Fuzhou City, China. We enrolled 580 patients with NAFLD and 580 healthy controls.

RESULTS

In the multivariate logistic regression analysis, the rs1800804 (-164 T/C) was associated with an increased risk of NAFLD, while the rs1057613 A/G and rs3805335 C/T SNPs were associated with a decreased risk of NAFLD. The cumulative effect of the rs1800804 (-164 T/C), rs1057613 and rs3805335 was estimated, and a significant increased trend in the risk of NAFLD with increasing genetic risk score was observed (adjusted P(trend) = 0.014). Furthermore, the results of haplotype analysis suggested that the haplotype GC in block 1 containing the -164 C allele was associated with an increased risk of NAFLD, while haplotype TGTTC in block 2 was associated with a decreased risk of NAFLD.

CONCLUSIONS

Our data show that MTTP genetic polymorphisms influence the susceptibility to developing NAFLD independently or jointly in the Han Chinese population.

Microsomal triglyceride transfer protein -164 T > C gene polymorphism and risk of cardiovascular disease: results from the EPIC-Potsdam case-cohort study

Background

The microsomal triglyceride transfer protein (MTTP) is encoded by the MTTP gene that is regulated by cholesterol in humans. Previous studies investigating the effect of MTTP on ischemic heart disease have produced inconsistent results. Therefore, we have tested the hypothesis that the rare allele of the -164T > C polymorphism in MTTP alters the risk of cardiovascular disease (CVD), depending on the cholesterol levels.

Methods

The -164T > C polymorphism was genotyped in a case-cohort study (193 incident myocardial infarction (MI) and 131 incident ischemic stroke (IS) cases and 1 978 non-cases) nested within the European Prospective Investigation into Cancer and Nutrition (EPIC)–Potsdam study, comprising 27 548 middle-aged subjects. The Heinz Nixdorf Recall study (30 CVD cases and 1 188 controls) was used to replicate our findings.

Results

Genotype frequencies were not different between CVD and CVD free subjects (P = 0.79). We observed an interaction between the -164T > C polymorphism and total cholesterol levels in relation to future CVD. Corresponding stratified analyses showed a significant increased risk of CVD (HR_additve = 1.38, 95% CI: 1.07 to 1.78) for individuals with cholesterol levels <200 mg/dL in the EPIC-Potsdam study. HR_additive was 1.06, 95% CI: 0.33 to 3.40 for individuals in the Heinz Nixdorf Recall study. A borderline significant decrease in CVD risk was observed in subjects with cholesterol levels ≥200 mg/dL (HR_additve = 0.77, 95% CI: 0.58 to 1.03) in the EPIC-Potsdam study. A similar trend was observed in the independent cohort (HR_additve = 0.60, 95% CI: 0.29 to 1.25).

Conclusions

Our study suggests an interaction between MTTP -164T > C functional polymorphism with total cholesterol levels. Thereby risk allele carriers with low cholesterol levels may be predisposed to an increased risk of developing CVD, which seems to be abolished among risk allele carriers with high cholesterol levels.

Cholesterol absorption status and fasting plasma cholesterol are modulated by the microsomal triacylglycerol transfer protein -493 G/T polymorphism and the usual diet in women

An important inter-individual variability in cholesterol absorption has been reported. It could result from polymorphisms in genes coding for proteins involved in the absorption process and in interaction with dietary intakes. To assess whether the extent of cholesterol absorption or synthesis is modified in adult women according to the -493 G/T polymorphism in the microsomal triglyceride transfer protein gene (MTP) and/or the habitual diet. Cholestanol and sitosterol, as well as desmosterol and lathosterol, surrogate markers of cholesterol absorption or synthesis, respectively, were analyzed in the fasting plasma of 69 middle-aged women under a Western-type diet (WD) and after 3 months on a low-saturated fat, low-cholesterol/Mediterranean-type diet (LFLCD). Genotypes for MTP -493G/T polymorphism were determined. Under an usual WD, subjects homozygous for the MTP -493 T allele exhibited higher (P < 0.05) fasting serum concentrations of cholestanol (199.0 ± 30.0 vs. 133 ± 7.4 × 10(2 )mmol/mol cholesterol) and lathosterol (188.7 ± 21.8 vs. 147.6 ± 9.1 × 10(2) mmol/mol cholesterol), as well as total cholesterol (7.32 ± 0.22 vs. 6.63 ± 0.12 mmol/l) compared to G carrier subjects. After 3 months on a LFLCD, level of absorption markers decreased in TT subjects with no change in synthesis ones, leading to values comparable to those measured in G carriers. The lowering of plasma total and LDL cholesterol due to dietary change was 2.4- and 2.3-fold greater in TT women than in G carriers. The polymorphism -493G/T in MTP modulates the level of cholesterol absorption but not synthesis in women under a WD, an effect abolished under a prudent LFLCD.

Linkage disequilibrium between four MTTP gene polymorphisms in a Mexican population

BACKGROUND

The microsomal triglyceride transfer protein plays an important role in the folding, assembling and secretion of lipoproteins that contain apoprotein B. Different polymorphisms in the MTTP gene have been associated with risk factors for coronary heart disease and diabetes, the first and fourth most common causes of death in Mexico, respectively.

AIM

The objective of this study was to assess allele, genotype and haplotype frequencies of six MTTP polymorphisms in an unselected Mexican population.

SUBJECTS AND METHODS

Six polymorphisms were analysed by DNA sequencing of polymerase chain reaction products in 155 Mexican individuals and Hardy-Weinberg equilibrium, genetic variability, linkage disequilibrium and neutrality test were evaluated.

RESULTS

The rare alleles of the six polymorphisms analysed had frequencies greater than 1% and their genotype distributions were in accordance with Hardy-Weinberg equilibrium. All three promoter and I/T 128 polymorphisms were in linkage disequilibrium. Twelve different haplotypes were observed; GATGGT (70.44%) and TTCGGC (13.91%) were the most common. Diversity patterns in this Mexican population deviate significantly from expectations of the standard neutral model for infinite allele.

CONCLUSION

The -493 G/T, -400 A/T, -164 T/C and I/T 128 polymorphisms can be useful for association studies in this population.

MTTP variants and body mass index, waist circumference and serum cholesterol level: Association analyses in 7582 participants of the KORA study cohort

The microsomal triglyceride transfer protein (MTTP) is a key regulator in the assembly and secretion of chylomicrons and very low density lipoprotein (VLDL) in the intestine and in liver. Associations between MTTP variants and traits of the metabolic syndrome are carried out in relatively small cohorts and are not consistent. We analysed MTTP polymorphisms in 7582 participants of the KORA study cohort. Seven htSNPs covering a 52kb region of the MTTP locus and two cSNPs (I128T, H297Q) were selected. A MTTP haplotype containing the minor allele of H297Q showed a significant decrease of -0.636 (95% CI: -1.226, -0.046; p=0.035) BMI units in females but not in males. In comparison to homozygous H-carriers for the major allele of the MTTP H297Q polymorphism, homozygous Q297Q carriers showed a significant decrease in BMI of -0.425B MI units (95% CI: -0.74, -0.12; p=0.007), in waist circumference of -0.990 cm (95% CI: 1.74, -0.24; p=0.01) and in total cholesterol of -0.039 mmol/l (95% CI: -0.07, 0; p=0.03). Heterozygous Q-carriers displayed a reduction in BMI of -0.183 BMI unit (95% CI: -0.33, -0.04; p=0.012), in waist circumference of -0.45 cm (95% CI: 0.8, -0.1; p=0.01) and in total cholesterol of -0.103 mmol/l (95% CI: -0.18, -0.03; p=0.01). Gender stratified statistics revealed a significant reduction of -0.657 BMI units (95% CI: -1.14, -0.18; p=0.007), -1.437 cm waist circumference (95% CI: -2.55, -0.32; p=0.01) and -0.052 mmol/l total cholesterol (95% CI: -0.1, -0.01; p=0.03) for females homozygous for the Q297Q polymorphism. Females carrying the Q-allele showed a decrease of -0.259 BMI unit (95% CI: -0.48, -0.04; p=0.023), -0.662 cm waist circumference (95% CI: -1.18, -0.14; p=0.01) and -0.111 mmol/l total cholesterol (95% CI: -0.21, -0.01; p=0.03). Our association analysis in a large population based study cohort provides evidence that the minor allele of the MTTP H297Q polymorphism is associated with lower BMI, waist circumference and total cholesterol in females but not in males.

Polymorphisms of microsomal triglyceride transfer protein in different hepatitis B virus-infected patients

AIM: To identify the two polymorphisms of microsomal triglyceride transfer protein (MTP) gene in the Chinese population and to explore their correlation with both hepatitis B virus (HBV) self-limited infection and persistent infection.

METHODS: A total of 316 subjects with self-limited HBV infection and 316 patients with persistent HBV infection (195 subjects without familial history), matched with age and sex, from the Chinese Han population were enrolled in this study. Polymorphisms of MTP at the promoter region -493 and at H297Q were determined by the allele specific polymerase chain reaction (PCR).

RESULTS: The ratio of males to females was 2.13:1 for each group and the average age in the self-limited and chronic infection groups was 38.36 and 38.28 years, respectively. None of the allelic distributions deviated significantly from that predicted by the Hardy-Weinberg equilibrium. There was a linkage disequilibrium between H297Q and -493G/T (D’ = 0.77). As the χ² test was used, the genotype distribution of MTP-493G/T demonstrated a significant difference between the self-limited infection group and the entire chronic group or the chronic patients with no family history (χ² = 8.543, P = 0.015 and χ² = 7.199, P = 0.019). The allele distribution at the MTP-493 position also demonstrated a significant difference between the study groups without family history (χ² = 6.212, P = 0.013). The T allele emerged as a possible protective factor which may influence the outcomes of HBV infection (OR: 0.59; 95% CI: 0.389-0.897).

CONCLUSION: The polymorphism of the MTP gene, T allele at -493, may be involved in determining the HBV infection outcomes, of which the mechanism needs to be further investigated.

Human fasting plasma concentrations of vitamin E and carotenoids, and their association with genetic variants in apo C-III, cholesteryl ester transfer protein, hepatic lipase, intestinal fatty acid binding protein and microsomal triacylglycerol transfer protein

Plasma concentrations of vitamin E and carotenoids are governed by several factors, including genetic factors. Single nucleotide polymorphisms (SNP) in some genes involved in lipid metabolism have recently been associated with fasting plasma concentrations of these fat-soluble micronutrients. To further investigate the role of genetic factors that modulate the plasma concentrations of these micronutrients, we assessed whether SNP in five candidate genes (apo C-III,CETP,hepatic lipase,I-FABPandMTP) were associated with the plasma concentrations of these micronutrients. Fasting plasma vitamin E and carotenoid concentrations were measured in 129 French Caucasian subjects (forty-eight males and eighty-one females). Candidate SNP were genotyped by PCR amplification followed by restriction fragment length polymorphisms. Plasma γ-tocopherol, α-carotene and β-carotene concentrations were significantly different (P < 0·05) in subjects who carried different SNP variants in hepatic lipase. Plasma α-tocopherol concentrations were significantly different in subjects who had different SNP variants in apo C-III and cholesteryl ester transfer protein (CETP). Plasma lycopene concentrations were significantly different (P < 0·05) in women who had different SNP variants in intestinal fatty acid binding protein (I-FABP). Finally, there was no effect of SNP variants in microsomal TAG transfer protein upon the plasma concentrations of these micronutrients. Most of the observed differences remained significant after the plasma micronutrients were adjusted for plasma TAG and cholesterol. These results suggest that apo C-III, CETP and hepatic lipase play a role in determining the plasma concentrations of tocopherols while hepatic lipase and I-FABP may modulate plasma concentrations of carotenoids.

Factors influencing the formation of small dense low-density lipoprotein particles in dependence on the presence of the metabolic syndrome and on the degree of glucose intolerance

BACKGROUND

Small dense low-density lipoprotein (LDL) particles are known to be especially atherogenic. Several mechanisms are involved in this atherogenicity.

AIMS

We wanted to look for the presence of small dense LDL particles depending on gender, metabolic syndrome (MS) and different degrees of glucose intolerance. Moreover, we looked for anthropometric factors and factors of lipid and carbohydrate metabolism that are associated with changes in the LDL size.

RESULTS

We studied 752 persons (330 males, 422 females; age 40 +/- 17 years). LDL particle size was estimated with polyacrylamide gel electrophoresis. Males had smaller LDL particles than females. Probands with the MS had smaller LDL particles than those without this syndrome. With rising plasma triglyceride (TG) levels more small dense LDL particles were seen. The highest proportion of these small dense LDL particles was observed in the subgroup of type 2 diabetic patients. In the whole material, the mean LDL diameter was correlated negatively with plasma TG and very low-density lipoprotein components (TG, cholesterol and proteins) and positively with high-density lipoprotein cholesterol. In a linear stepwise regression analysis different significant factors influencing the LDL size were found in the whole population, in normoglycaemic probands, in persons with impaired glucose tolerance, in type 2 diabetic patients and in type 2 diabetic patients injecting insulin.

CONCLUSIONS

Our data point to different mechanisms of the formation of small dense LDL particles in dependence on the degree of glucose intolerance. Moreover, the target values for plasma TG should be set lower.

Microsomal triglyceride transfer protein 493-T variant is associated with resistin levels and C-reactive protein

BACKGROUND

The microsomal triglyceride transfer protein (MTP) is a heterodimeric lipid transfer protein that consists of a large unique 97-kDA subunit and protein disulfide isomerase. MTP is involved in the assembly of apoB-containing lipoprotein and enables the secretion of VLDLs by the liver and chylomicrons by the intestine. The MTP gene is highly polymorphic. The less common T variant has been associated with the reduction of plasma LDL-cholesterol levels and with an increased risk in coronary heart disease. We hypothesized that MTP polymorphism could be associated to LDL-cholesterol levels and proinflammatory cytokines, such as resistin.

METHODS AND RESULTS

The -493G/T MTP gene polymorphism was investigated in 290 subjects. Subjects carrying the TT genotype had lower level of LDL-cholesterol and higher serum resistin levels than individual carrying one or two copies of the -493G allele. After adjustments for age, BMI, waist circumference, alcohol intake and exercise levels, a significant direct association was evident between hs-CRP and resistin levels and the presence of the TT genotype in a multiple regression model.

CONCLUSION

This study supports the notion that the rare MTP-493T/T genotype is associated both with higher levels of inflammatory parameters and with low levels of LDL-cholesterol. Prospective data are needed to investigate if the association between CVD and the MTP-493T/T genotype might be due to the increased sub-clinical proinflammatory state associated with this mutation.

Polymorphism in microsomal triglyceride transfer protein: a link between liver disease and atherogenic postprandial lipid profile in NASH?

Nonalcoholic fatty liver disease (NAFLD) is emerging as an independent cardiovascular risk factor, but mechanism(s) linking fatty liver to atherosclerosis are unknown. Microsomal triglyceride transfer protein (MTP) -493 G/T polymorphism modulates circulating lipid and lipoprotein levels in different subsets and has been linked to NAFLD. The impact of MTP -493 G/T polymorphism, adipokines, and diet on postprandial lipoprotein profile and liver disease was assessed in nonalcoholic steatohepatitis (NASH). Plasma lipids, triglyceride-rich lipoprotein subfractions, high-density lipoprotein-C (HDL-C), and oxidized low-density lipoprotein (LDL) after an oral fat load were cross-sectionally correlated to MTP -493 G/T polymorphism, dietary habits, adipokines, and liver histology in 29 nonobese nondiabetic patients with NASH and 27 healthy controls. The severity of liver histology, the magnitude of triglycerides (Tg), free fatty acid (FFA), and LDL-conjugated diene responses, and the fall in HDL-C and apoA1 were significantly higher in NASH G/G (66% of patients) than in the other genotypes, despite similar adipokine profile and degree of insulin resistance. Postprandial large intestinal very-low-density lipoprotein (VLDL) subfraction A increases independently predicted Tg (beta=0.48; P=.008), FFA (beta=0.47; P=0.010), HDL-C (beta=0.42; P=0.009), and LDL-conjugated diene (beta=0.52; P=0.002) responses. VLDL A apoB48 response was independently associated with liver steatosis (OR: 2.4; CI 1.7-9.6; P=0.031). Postprandial LDL-conjugated diene response predicted severe necroinflammation (OR: 3.3; CI 1.4-9.7; P=0.016) and fibrosis (OR: 2.8; CI 1.0-8,5; P=0.030); postprandial apoA1 fall predicts severe fibrosis (OR: 2.1; CI: 1.5-6.1; P=0.015).

CONCLUSION

MTP -493 G/T polymorphism may impact NASH by modulating postprandial lipemia and lipoprotein metabolism; homozygous GG carriers have a more atherogenic postprandial lipid profile than the other genotypes, independently of adipokines and insulin resistance.

Absence of Relationship Between MTTP Haplotypes and Longevity

BACKGROUND

Polymorphisms for the microsomal triglyceride transfer protein (MTTP) gene have been associated with longevity and with lower risk for cardiovascular mortality. However, the association of MTTP with longevity has been contested in a large German collection of nonagenarians and centenarians.

METHODS

We made a detailed characterization of MTTP haplotype carrier status in a cohort of 1398 old men and women (mean age 78 years) and a population-based cohort (n = 777) of younger controls (mean age 40 years) in Oxford, England.

RESULTS

There were no significant differences in haplotypes for MTTP gene between the younger and older age groups.

CONCLUSION

This study, which adopted a more detailed genetic analysis of the MTTP gene in a large case-control study of older people provides reliable evidence against any significant association of the MTTP gene with longevity.

Functional analysis of promoter variants in the microsomal triglyceride transfer protein (MTTP) gene

The microsomal triglyceride transfer protein (MTTP) is required for the assembly and secretion of apolipoprotein B (apoB)-containing lipoproteins from the intestine and liver. According to this function, polymorphic sites in the MTTP gene showed associations to low-density lipoprotein (LDL) cholesterol and related traits of the metabolic syndrome. Here we studied the functional impact of common MTTP promoter polymorphisms rs1800804:T>C (-164T>C), rs1800803:A>T (-400A>T), and rs1800591:G>T (-493G>T) using gene-reporter assays in intestinal Caco-2 and liver Huh-7 cells. Significant results were obtained in Huh-7 cells. The common MTTP promoter haplotype -164T/-400A/-493G showed about two-fold lower activity than the rare haplotype -164C/-400T/-493T. MTTP promoter mutant constructs -164T/-400A/-493T and -164T/-400T/-493T exhibited similar activity than the common haplotype. Activities of mutants -164C/-400A/-493G and -164C/-400A/-493T resembled the rare MTTP promoter haplotype. Electrophoretic mobility shift assays (EMSAs) revealed higher binding capacity of the transcriptional factor Sterol regulatory element binding protein1a (SREBP1a) to the -164T probe in comparison to the -164C probe. In conclusion, our study indicates that the polymorphism -164T>C mediates different activities of common MTTP promoter haplotypes via SREBP1a. This suggested that the already described SREBP-dependent modulation of MTTP expression by diet is more effective in -164T than in -164C carriers.

Chromosome 4q25, microsomal transfer protein gene, and human longevity: novel data and a meta-analysis of association studies

Recently, chromosome 4q25 was linked to exceptional human longevity, and a haplotype of the positional candidate microsomal transfer protein (MTP) gene was associated to the phenotype in U.S. Caucasians. We investigated whether linkage to 4q25 could be detected in 164 nonagenarian sibships of the Leiden Longevity Study. Additionally, we compared the MTP -493G/T and Q95H allele and haplotype frequencies in the Leiden Longevity Study (379 nonagenarians, 525 of their offspring, and 251 partners of their offspring) and in the Leiden 85-Plus Study (655 octogenarians and 244 young controls). The latter study population was followed for at least 7 years, providing the opportunity to perform also prospective analyses using the longitudinal data. We found neither evidence for linkage at 4q25 nor association of the MTP locus with longevity in nonagenarian individuals. Meta-analyses of all previous studies implied that the association in U.S. Caucasians may have its source in admixture of the U.S. control population rather than in the genetic effect of the locus on exceptional longevity.

A common functional exon polymorphism in the microsomal triglyceride transfer protein gene is associated with type 2 diabetes, impaired glucose metabolism and insulin levels

The microsomal triglyceride transfer protein (MTP) is required for the assembly and secretion of apolipoprotein B-containing lipoproteins. Emerging evidence has indicated that the functional MTP exon polymorphism I128T is associated with dyslipidemia and other traits of the insulin-resistance syndrome, and the T128 variant seems to confer a reduced stability of MTP, resulting in reduced binding of LDL particles. The aim of the study was to elucidate the association of this MTP polymorphism with parameters of postprandial metabolism. A total of 716 male subjects from a postprandially characterized cohort (MICK) and a nested case-control study (EPIC) of 190 incident type 2 diabetes cases and 380 sex- or age-matched controls were genotyped for the I128T exon polymorphism. In comparison to homozygote subjects of the wild allele, carriers of the less common allele of the MTP T128 genotype showed significantly lower postprandial insulin levels (P=0.017), lower diastolic blood pressure (P=0.049) and had a lower prevalence of impaired glucose metabolism and diabetes type 2 (P=0.03) in the MICK. Consistent with this, we found a lower incidence of type 2 diabetes in male subjects of the nested case-control study in the T128 genotype (P=0.007). These results suggest that the rare allele of the MTP I128T polymorphism may be protective against impaired glucose tolerance, type 2 diabetes and other parameters of the metabolic syndrome.

Microsomal triglyceride transfer protein -493T variant reduces IDL plus LDL apoB production and the plasma concentration of large LDL particles

The microsomal triglyceride transfer protein (MTP) is essential for the synthesis and secretion of apolipoprotein B (apoB)-containing lipoproteins. We investigated the role the MTP -493G/T gene polymorphism in determining the apoB-100 secretion pattern and LDL heterogeneity in healthy human subjects. Groups of carriers of the T and the G variants (n = 6 each) were recruited from a cohort of healthy 50-yr-old men. Kinetic studies were performed by endogenous [(2)H(3)]leucine labeling of apoB and subsequent quantification of the stable isotope incorporation. apoB production rates, metabolic conversions, and eliminations were calculated by multicompartmental modeling (SAAM-II). LDL subfraction distribution was analyzed in the entire cohort (n = 377). Carriers of the MTP -493T allele had lower plasma LDL apoB and lower concentration of large LDL particles [LDL-I: 136 +/- 57 (TT) vs. 175 +/- 55 (GG) mg/l, P < 0.01]. Kinetic modeling suggested that MTP -493T homozygotes had a 60% lower direct production rate of intermediate-density lipoprotein (IDL) plus LDL compared with homozygotes for the G allele (P < 0.05). No differences were seen in production rates of large and small VLDL, nor were there any differences in metabolic conversion or elimination rates of apoB between the genotype groups. This study shows that a polymorphism in the MTP gene affects the spectrum of endogenous apoB-containing lipoprotein particles produced in humans. Reduced direct production of LDL plus IDL appears to be related to lower plasma concentrations of large LDL particles.

Influence of microsomal triglyceride transfer protein promoter polymorphism −493 GT on fasting plasma triglyceride values and interaction with treatment response to atorvastatin in subjects with heterozygous familial hypercholesterolaemia

Familial hypercholesterolaemia (FH) is an autosomal dominant disease characterized by elevated levels of low-density lipoprotein-cholesterol (LDL-C). Phenotypic expression is highly variable, being influenced by diet, age, gender, body mass index, apolipoprotein E genotype and type of LDL-receptor gene mutation. Microsomal triglyceride (TG) transfer protein (MTP) is a protein involved in lipid metabolism. Polymorphism MTP -493 GT has been shown to modulate lipid levels in several populations. To analyse the effect of this polymorphism in the lipid phenotype expression of FH and treatment response, we studied a sample of 222 Spanish FH patients, of whom 147 were studied before and after treatment with 20 mg of atorvastatin daily during 6 weeks. The variant was analysed by polymerase chain reaction amplification and single-strand confirmation polymorphism. Treatment reduced LDL-C, total cholesterol and TGs. Baseline fasting TGs and very-low-density lipoprotein cholesterol levels were lower in female T allele carriers (TG: 111+/-51 mg/dl GG, 89+/-35 mg/dl GT, 83+/-26 mg/dl TT, P=0.022; very-low-density lipoprotein cholesterol: 24+/-13 mg/dl GG, 16+/-5 mg/dl GT, 17+/-5 mg/dl TT, P=0.018). Triglyceride response to atorvastatin was modulated by this polymorphism in men (P=0.009), but not in women, although differences between genotypes were maintained after treatment. In conclusion, the MTP -493 GT polymorphism modulates pre- and post-treatment plasma TG values of FH in Spanish subjects in a gender-specific way. Other environmental and genetic factors likely also modulate this response.

Genetic polymorphisms affecting the phenotypic expression of familial hypercholesterolemia

The clinical expression of heterozygous familial hypercholesterolemia (FH) is highly variable even in patients carrying the same LDL receptor (LDL-R) gene mutation. This variability might be due to environmental factors as well as to modifying genes affecting lipoprotein metabolism. We investigated Apo E (2, 3, 4), MTP (-493G/T), Apo B (-516C/T), Apo A-V (-1131T/C), HL (-514C/T and -250G/A), FABP-2 (A54T), LPL (D9N, N291S, S447X) and ABCA1 (R219K) polymorphisms in 221 unrelated FH index cases and 349 FH relatives with defined LDL-R gene mutations. We found a significant and independent effect of the following polymorphisms on: (i) plasma LDL-C (Apo E, MTP and Apo B); (ii) plasma HDL-C (HL, FABP-2 and LPL S447X); (iii) plasma triglycerides (Apo E and Apo A-V). In subjects with coronary artery disease (CAD+), the prevalence of FABP-2 54TT genotype was higher (16.5% versus 5.2%) and that of ABCA1 219RK and KK genotypes lower (33.0% versus 51.5%) than in subjects with no CAD. Independent predictors of increased risk of CAD were male sex, age, arterial hypertension, LDL-C level and FABP-2 54TT genotype, and of decreased risk the 219RK and KK genotypes of ABCA1. These findings show that several common genetic variants influence the lipid phenotype and the CAD risk in FH heterozygotes.

Guidelines for the diagnosis and management of heterozygous familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism characterized by very high plasma concentrations of low density lipoprotein cholesterol (LDLc), tendon xanthomas and increased risk of premature coronary heart disease (CHD). FH is a public health problem throughout the world. There are 10,000,000 people with FH worldwide, mainly heterozygotes, and approximately 85% of males and 50% of females with FH will suffer a coronary event before 65 years old if appropriate preventive efforts are not implemented. Early identification of persons with FH and their relatives, and the early start of treatment are essential issues in the prevention of premature cardiovascular disease (CVD) and death in this population. However, guidelines for the general population formally exclude FH from their diagnostic and treatment recommendations. These guidelines have been elaborated by a group of international experts with the intention to answer the main questions about heterozygous FH (heFH) subjects that physicians worldwide face in the diagnosis and management of these patients.

Soluble epoxide hydrolase variant (Glu287Arg) modifies plasma total cholesterol and triglyceride phenotype in familial hypercholesterolemia: intrafamilial association study in an eight-generation hyperlipidemic kindred

Plasma lipid and lipoprotein in general reflect the complex influences of multiple genetic loci, for instance, even familial hypercholesterolemia (FH), a representative example of monogenic hyperlipidemia, often presents with phenotypic heterogeneity. In the course of investigating familial coronary artery disease in Utah, we studied 160 members of an eight-generation extended family of FH in which 69 members were affected with type IIa hyperlipoproteinemia (HLPIIa; high plasma cholesterol) and ten with type IIb hyperlipoproteinemia (HLPIIb; high plasma cholesterol as well as plasma triglyceride). Soluble epoxide hydrolase ( EPHX2, sEH) plays a role in disposition of epoxides in plasma lipoprotein particles. Intrafamilial correlation analysis of the modifier effect of Glu287Arg substitution in the EPHX2 gene was carried out among 79 LDLR mutation carriers and 81 noncarriers. In the carriers, plasma cholesterol levels were elevated among carriers of the 287Arg allele (mean +/- SD=358 +/- 72 mg/dl) in comparison with 287Glu homozygotes (mean +/- SD=302 +/- 72 mg/dl) (p=0.0087). Similarly, in the LDLR mutation carriers, the plasma triglyceride levels were elevated among carriers of the 287Arg allele (mean +/- SD=260 +/- 100 mg/dl) in comparison with 287Glu homozygotes (mean +/- SD=169 +/- 83 mg/dl) (p=0.020). No such gene-interactive effect was observed among noncarriers of the LDLR mutation. Half of the patients who presented with HLPIIb had inherited a defective LDLR allele as well as an EPHX2-287Arg allele, whereas the majority who presented with HLPIIa had a defective LDLR allele but not an EPHX2-287Arg allele. These results indicate a significant modification of the phenotype of FH with defective LDLR allele by EPHX2-287Arg variation in our studied kindred.

Apolipoprotein H variant modifies plasma triglyceride phenotype in familial hypercholesterolemia: a molecular study in an eight-generation hyperlipidemic family

In the course of investigating familial coronary artery disease in Utah, we studied 196 members of an eight-generation extended family of familial hypercholesterolemia (FH), in which 73 members were affected with type IIa hyperlipoproteinemia (HLPIIa; high plasma cholesterol) and 11 members with type IIb hyperlipoproteinemia (HLPIIb; high plasma cholesterol as well as plasma triglyceride). A splice-site mutation of the LDL receptor (LDLR) gene (IVS14 + G > A) co-segregated with elevated plasma cholesterol among all the members, but not with the elevated plasma triglyceride and VLDL cholesterol levels seen in HLPIIb patients. The apolipoprotein H (apoH) gene plays a role in plasma triglyceride removal and lipoprotein lipase enhancement. Intra-familial correlation analysis of the modifier effect of Val247Leu substitution in the apoH gene was carried out among 84 LDLR-mutation carriers and 112 non-carriers. When plasma triglyceride levels in the LDLR-mutation carriers were compared, the values were lowest among V/V homozygotes (mean +/- SD = 145 +/- 53 mg/dl), highest in L/L homozygotes (277 +/- 177 mg/dl), and intermediate among V/L heterozygotes (191 +/- 102 mg/dl) (p = 0.0015). All eleven patients who presented with HLPIIb had inherited both the defective LDLR allele and an apoH 247Leu allele, whereas all 45 carriers of the defective LDLR allele not carrying the apoH Leu allele presented with HLPIIa but not HLPIIb (p = 0.0001). These results indicate a significant modification of the phenotype of FH with a defective LDLR allele, by apoH Leu variation in our studied family.

Growth hormone receptor variant (L526I) modifies plasma HDL cholesterol phenotype in familial hypercholesterolemia: intra-familial association study in an eight-generation hyperlipidemic kindred

Defect of growth hormone receptor (GHR) is classically known to cause Laron syndrome, characterized by short stature, specific facial appearance, elevated serum growth hormone levels, and decreased insulin-like growth factor I levels. In addition, an increased cardiovascular risk due to elevated plasma total and LDL cholesterol levels marks another feature of the disease. Growth hormone (GH) plays an important role in the regulation of lipoprotein metabolism. GH status was found to be an independent determinant of plasma total cholesterol and triglyceride levels in humans. We studied a total of 207 members of eight-generation extended family of familial hypercholesterolemia (FH) in which affected members presented with various lipoprotein phenotypes. Intra-familial correlation analysis of a modifier effect of a Leu526Ile substitution in GHR gene was carried out among 95 carriers for LDL receptor gene (LDLR) mutation and 112 non-carriers. When plasma high-density lipoprotein cholesterol (HDL-c) levels in the LDLR-mutation carriers were compared, a significant lowering effect of HDL-c was observed with the Leu allele; the values were lowest among Leu/Leu homozygotes (mean +/- SD = 37 +/- 2 mg/dl), highest in Ile/Ile homozygotes (50 +/- 4 mg/dl), and intermediate among Leu/Ile heterozygotes (41 +/- 2 mg/dl) (P = 0.0021). The results indicate a significant modification of the phenotype of FH with the defective LDLR allele, by GHR Leu variation in the kindred studied.

DNA testing for familial hypercholesterolemia: improving disease recognition and patient care

Cardiovascular disease is the leading cause of death worldwide and, like most chronic diseases, it has major genetic and environmental components. Among patients with coronary heart disease onset before the age of 55, about 5% of cases are attributable to heterozygous familial hypercholesterolemia (FH), a disease following autosomal dominant inheritance. About 50% of individuals with FH die before the age of 60 due to myocardial infarction. The frequency of FH is estimated to be 1 : 500. FH is related to mutations in the low-density lipoprotein (LDL)-cholesterol LDL-receptor gene and apolipoprotein B (apoB) gene. The identification of individuals with FH has been based on lipid levels and segregation of lipid levels within the family. However, phenotypes are overlapping and family history is not always informative. Therefore, a DNA-based genetic test for FH appears to offer the best alternative. The DNA test gives a simple yes/no answer. The FH test is a definitive tool for the identification of affected family members. The approach of targeted family genetic screening to find new patients is faster and more reliable compared with a biochemical form of screening. Early identification and efficient treatment of such patients is important and highly cost effective. There is evidence to suggest that the nature of the LDL-receptor (LDLR) mutation influences the degree of cholesterol lowering achieved by HMG-CoA reductase inhibitors (statins). The observed differences in the LDL-cholesterol (LDL-C) responses to these drugs among the various LDLR gene mutations are not yet completely understood. The relationships shown between LDLR mutation types and lipid levels, and the response of lipid levels to HMG-CoA reductase inhibitor treatment, will have to be investigated within the framework of pharmacogenetic studies. The variables, which are important in determining the overall atherosclerosis risk, are the result of combined activity in a dynamic network of numerous genes and environment. Candidate genes for atherosclerosis need to be further tested and validated. Future research should be directed at determining the significance of such targets, which patients with FH are at particularly high risk of premature cardiovascular disease, and which environmental factors are effective in modulating this risk. Genetics-based diagnostics will complement identification of FH while improving cardiovascular risk prediction, prevention of disease and treatment efficacy.

Improvement in blood lipid levels by dietary sn-1,3-diacylglycerol in young women with variants of lipid transporters 54T-FABP2 and -493g-MTP

In a double-blind parallel-group study, serum lipids and visceral fat/total fat ratio in young women (n=49) with variants of lipid transporters, i.e., fatty acid binding protein 2 (FABP2) and microsomal triglyceride transfer protein (MTP), were analyzed by substituting dietary triacylglycerol (TAG) with sn-1,3-diacylglycerol (DAG). All subjects, including some with the hyperlipidemia-prone genotypes Ala54Thr of FABP2 and c-493g of MTP, received DAG or TAG (20 g/day) for 8 weeks. Reductions of serum lipids from weeks 4 to 8 in FABP2-Ala54Thr heterozygotes and MTP -493g homozygotes were significantly different between the DAG and TAG groups (p<0.05, p<0.01). Visceral fat/total fat (%), as determined by computed tomography (CT), was lower in FABP2-Ala54Thr heterozygotes (p<0.05) of the DAG group. The apoCII/CIII ratio was higher in the DAG group than in the TAG group (p<0.01). Other variants of lipid metabolism, including peroxisome proliferator activated receptors (PPARs) alpha and gamma and SREBP cleavage-activating protein (SCAP), were only slightly affected by dietary DAG.

CONCLUSION

improvement of serum lipid profiles and visceral fat/total fat ratio (CT) was potentiated by DAG intake in subjects with hyperlipidemia-prone genotypes (Ala54Thr heterozygotes of FABP2 and -493g homozygotes of MTP).

A common variant in the ABCA1 gene is associated with a lower risk for premature coronary heart disease in familial hypercholesterolaemia

Familial hypercholesterolaemia (FH) is a common autosomal codominant hereditary disease caused by defects in the LDL receptor (LDLR) gene, and one of the most common characteristics of affected subjects is premature coronary heart disease (CHD). In heterozygous FH patients, the clinical expression of FH is highly variable in terms of the severity of hypercholesterolaemia and the age of onset and severity of CHD. Identification of mutations in the ATP binding cassette transporter 1 (ABCA1) gene in patients with Tangier disease, who exhibit reduced HDL cholesterol and apolipoprotein A1 concentrations and premature coronary atherosclerosis, has led us to hypothesise that ABCA1 could play a key role in the onset of premature CHD in FH. In order to know if the presence of the R219K variant in the ABCA1 gene could be a protective factor for premature CHD in FH, we have determined the presence of this genetic variant by amplification by PCR and restriction analysis in a group of 374 FH subjects, with and without premature CHD. The K allele of the R219K variant was significantly more frequent in FH subjects without premature CHD (0.32, 95% CI 0.27 to 0.37) than in FH subjects with premature CHD (0.25, 95% CI 0.21 to 0.29) (p<0.05), suggesting that the genetic variant R219K in ABCA1 could influence the development and progression of atherosclerosis in FH subjects. Moreover, the K allele of the R219K polymorphism seems to modify CHD risk without important modification of plasma HDL-C levels, and it appears to be more protective for smokers than non-smokers.

Small, dense low-density lipoprotein: risk or myth?

Based on the particle diameter of the major subpopulation of low-density lipoprotein (LDL) in plasma, an individual may be classified either as having phenotype A (desirable phenotype; large, buoyant LDL) or phenotype B (high risk; small, dense LDL). This article reviews the clinical significance of LDL particle diameter determination and proposes a strategy for incorporating this information in the new guidelines of the National Cholesterol Education Program's Adult Treatment Panel III.

Garlic inhibits microsomal triglyceride transfer protein gene expression in human liver and intestinal cell lines and in rat intestine

Epidemiologic studies have suggested that fresh garlic has lipid-lowering activity. Because the microsomal triglyceride transfer protein (MTP) plays a pivotal role in the assembly and secretion of apolipoprotein B (apoB)-containing lipoproteins, we evaluated the effect of garlic on the expression of the MTP gene in vitro in cell lines and in vivo in rats. Fresh garlic extract (FGE) reduced MTP mRNA levels in both the human hepatoma HepG2 and intestinal carcinoma Caco-2 cells in dose-dependent fashion; significant reductions were detected with 3 g/L FGE. Maximal 72 and 59% reductions, respectively, were observed with 6 g/L FGE. To evaluate the in vivo effect of garlic on MTP gene expression, rats were given a single oral dose of fresh garlic homogenate (FGH), with hepatic and intestinal MTP mRNA measured 3 h after dosing. Rats fed FGH had significantly (46% of the control) lower intestinal MTP mRNA levels compared with the control rats, whereas hepatic MTP mRNA levels were not affected. These results suggest a new mechanism for the hypolipidemic effect of fresh garlic. Long-term dietary supplementation of fresh garlic may exert a lipid-lowering effect partly through reducing intestinal MTP gene expression, thus suppressing the assembly and secretion of chylomicrons from intestine to the blood circulation.

Phenotypic variability in familial hypercholesterolaemia: an update

Heterozygous familial hypercholesterolaemia is among the most common inherited dominant disorders, and is characterized by severely elevated LDL-cholesterol levels and premature cardiovascular disease. Although the cause of familial hypercholesterolaemia is monogenic, there is a substantial variation in the onset and severity of atherosclerotic disease symptoms. Additional atherogenic risk factors of environmental, metabolic and genetic origin, in conjunction with the LDL receptor defect, are presumed to influence the clinical phenotype in familial hypercholesterolaemia. The present review discusses recent developments in this field.