Contribution of mutations in low density lipoprotein receptor (LDLR) and lipoprotein lipase (LPL) genes to familial combined hyperlipidemia (FCHL): a reappraisal by using a resequencing approach.

BACKGROUND: Defective low-density lipoprotein receptor (LDLR) and lipoprotein lipase (LPL) alleles have been implicated in familial combined hyperlipidemia (FCHL). However, their contribution might have been influenced by diagnostic criteria. This study was aimed to reassess the frequency of rare and common variants in LDLR and LPL in FCHL individuals classified with stringent criteria. METHODS: LDLR and LPL were resequenced in 208 FHCL and 171 controls. Variants were classified as loss- (LOF) or gain-of-function (GOF) based upon in silico prediction, familial segregation and available functional data. RESULTS: Eight LOF variants were detected in LDLR, 6 of which were missense and 2 were predicted to disrupt normal splicing; all were present at heterozygous state. They were found in 10 FCHL but not in controls, thus indicating that 4.8% of FCHL individuals should be reclassified as FH. LDL-C (positive) and BMI (negative) were the strongest predictors of LDLR mutations with LDL-C 181 mg/dl being the best threshold for diagnosing the presence of dysfunctional LDLR alleles. The cumulative prevalence of definite LPL defective alleles (1 rare and 2 common heterozygous missense variants) was comparable between FCHL and controls (10.1% vs. 10.5%). Conversely, the LPL GOF variant p.Ser474* showed a lower frequency in FCHL than in controls (13.5% vs. 24.0%, p = 0.008). Overall, LOF LPL variants did not show a TG-modulating effect. CONCLUSIONS: Our findings indicate that, in well characterized FCHL individuals, variants in LDLR and LPL provide a small contribution to this dyslipidemia, thus limiting the need for such genetic testing.

Circulating PCSK9 is a strong determinant of plasma triacylglycerols and total cholesterol in homozygous carriers of apolipoprotein ε2.

Homozygous carriers of the apolipoprotein ε2 allele are at risk of type III hyperlipidaemia, but do not necessarily develop this lipid disorder. In the present study, we have investigated the role of circulating PCSK9 (pro-protein convertase subtilisin kexin type 9), an important regulator of LDL (low-density lipoprotein) receptor expression, in the development of this hyperlipidaemic phenotype. In an observational study, plasma PCSK9 was measured in homozygous carriers of apolipoprotein ε2 (ε2/ε2; n=12), normal controls (n=72) and hypertriglyceridaemic patients with FCHL (familial combined hyperlipidaemia; n=38), who served as a hyperlipidaemic reference group. Cholesterol, triacylglycerols (triglycerides) and apolipoprotein B content in VLDL (very-low-density lipoprotein) and LDL particles was determined by ultracentrifugation in ε2/ε2 and FCHL patients. Median circulating PCSK9 levels did not differ between ε2/ε2 carriers compared with controls and hypertriglyceridaemic FCHL patients (84.5 compared with 82.0 and 84.9 ng/ml; P=0.2 and 0.6 respectively). Circulating PCSK9 was associated with total cholesterol and triacylglycerols levels in ε2/ε2 carriers (P<0.05). These associations were stronger in ε2/ε2 carriers when compared with controls (P values for interaction=0.01 and 0.02 respectively). A direct comparison with FCHL patients demonstrated a similar discrepancy for the association with plasma triacylglycerols and also VLDL-apolipoprotein B, cholesterol and triacylglycerols (P value for interaction=0.01, 0.01, 0.03 and 0.03 respectively). Plasma PCSK9 is associated with type III hyperlipidaemia. Its strong relationship with plasma triacylglycerols and total cholesterol distinguishes ε2/ε2 carriers from controls and another type of dyslipidaemia, which provides valuable information regarding the pathogenesis of this complex dyslipidaemia. Furthermore, these results suggest that patients with type III hyperlipidaemia may benefit from PCSK9-antagonizing therapy.

Association of stearoyl-CoA desaturase 1 activity with familial combined hyperlipidemia.

OBJECTIVE: Stearoyl-CoA desaturase 1 (SCD1) is the rate-limiting enzyme involved in the synthesis of monounsaturated fatty acids, and in mice SCD1 activity is associated with plasma triglyceride levels. We used the fatty acid desaturation index (the plasma ratio of 18:1/18:0) as a marker of SCD1 activity to investigate the relationship of SCD1 to familial combined hyperlipidemia (FCHL). METHODS AND RESULTS: The fatty acid desaturation index was measured in 400 individuals from 18 extended FCHL pedigrees. FCHL-affected individuals exhibited increased SCD1 activity when compared to unrelated controls (P < 0.0001). The fatty acid desaturation index was found to be highly heritable (h(2) = 0.48, P = 2.2 x 10(-11)) in this study sample. QTL analysis in 346 sibling pairs from 18 FCHL families revealed suggestive linkage of the desaturation index to chromosomes 3p26.1 to 3p13 (z = 2.7, P = 0.003), containing the peroxisome proliferator-activated receptor gamma (PPARgamma) gene, and 20p11.21 to 20q13.32 (z = 1.7, P = 0.04), containing the hepatocyte nuclear factor 4, alpha (HNF4alpha) gene. A specific haplotype of HNF4alpha was found to be associated with the desaturation index in these FCHL families (P = 0.002). CONCLUSIONS: Our results demonstrate that the fatty acid desaturation index is a highly heritable trait that is associated with the dyslipidemia observed in FCHL.

Vascular remodeling and prothrombotic markers in subjects affected by familial combined hyperlipidemia and/or metabolic syndrome in primary prevention for cardiovascular disease.

Recent evidences suggest that modulation of vascular structure by matrix metalloproteinases (MMPs) could be a main determinant of acute cardiovascular events in high-risk subjects. The authors consecutively selected 46 subjects affected by familial combined hyperlipidemia (FCH), 44 by metabolic syndrome (MS), 44 by FCH and MS, and 40 healthy subjects. All these subjects were firstly diagnosed and not treated with lipid-lowering, antihypertensive, or antidiabetic drugs. A 12-h fasting blood sample was obtained from each patient, and plasma levels of MMP-2 and MMP-9 were measured together with their tissue inhibitors and a full set of laboratory cardiovascular disease markers. MMP-2 plasma levels were not significantly different among the considered groups. MMP-9, tissue inhibitor of MMP (TIMP)-1, and TIMP-2 are significantly higher in FCH (p < .001) and MS (p < .001) patients than in healthy controls, and they are also higher in MS patients than in FCH ones (p < .001). TIMP-1 (p < .001) and TIMP-2 (p < .001), but not MMP-9, are also significantly higher in subjects with MS associated to FCH than in patients with MS alone. No specific correlation among MMPs, TIMPs, and the other studied parameters has been observed in the whole sample and in the four above-defined subgroups. MMP-9, TIMP-1, and TIMP-2 plasma levels could be significant determinant and/or diagnostic markers of MS but not of FCH. However, the superposition of MS on FCH further increases the plasma level of these parameters. The prognostic value of this observation has to be evaluated.

Five-year follow-up of waist circumference, insulin and ALT levels in familial combined hyperlipidaemia.

INTRODUCTION: Familial combined hyperlipidemia (FCHL), an entity with many features of the metabolic syndrome, is characterized by changes in cholesterol and triglyceride phenotype over time. This study was conducted to investigate the relation of alanineaminotransferase (ALT) levels, used as a surrogate for the amount of hepatic fat, with the switch in triglyceride phenotype and the increased susceptibility to develop hypertriglyceridemia in FCHL. METHODS: Body mass index, waist circumference, plasma triglycerides, insulin and ALT levels were measured in 145 FCHL family members and 54 spouses at baseline and after a five-year follow-up. RESULTS: A switch from normotriglyceridemia to hypertriglyceridemia or vice versa, as observed in 22 of 145 FCHL family members, was associated with changes in plasma ALT levels (p=0.001), but not with insulin levels or waist circumference. In five-year follow-up, an intra-individual relation was observed between waist circumference and both plasma triglycerides, insulin and ALT levels. For each waist circumference FCHLpatients, but not their normolipidemic relatives, exhibited higher triglyceride and insulin levels than spouses (p<0.001). Remarkably, both FCHL patients and the normolipidemic relatives showed higher ALT levels for each waist circumference as compared to spouses(p<0.001 for FCHL patients, p=0.035 for normolipidemic relatives). CONCLUSION: The present study shows that the longitudinal relation abdominal obesity-ALT is more specific for all FCHL family members, i.e. patients and their normolipidemic relatives, than the relation abdominal obesity-triglycerides. Additionally,the association of ALT with the switch in triglyceride phenotype suggests a central role of the liver in the pathogenesis of FCHL.

Genes implicados en la hiperlipemia familiar combinada / Genes involved in the familial combined hyperlipidemia

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Determinants of low HDL levels in familial combined hyperlipidemia.

In familial combined hyperlipidemia (FCHL), affected family members frequently have reduced levels of HDL cholesterol, in addition to elevated levels of total cholesterol and/or triglycerides (TGs). In the present study, we focused on those determinants that are important regulators of HDL cholesterol levels in FCHL, and measured postheparin plasma activities of hepatic lipase (HL), lipoprotein lipase, cholesterol ester transfer protein, and phospholipid transfer protein (PLTP) in 228 subjects from 49 FCHL families. In affected family members (n = 88), the levels of HDL cholesterol, HDL2 cholesterol, HDL3 cholesterol, and apolipoprotein A-I were lower than in unaffected family members (n = 88) or spouses (n = 52). The main change was the reduction of HDL2 cholesterol by 25.4% in affected family members (P < 0.001 vs. unaffected family members; P = 0.003 vs. spouses). Affected family members had higher HL activity than unaffected family members (P = 0.001) or spouses (P = 0.013). PLTP activity was higher in affected than unaffected family members (P = 0.025). In univariate correlation analysis, a strong negative correlation was observed between HL activity and HDL2 cholesterol (r = -0.339, P < 0.001). Multivariate regression analysis demonstrated that gender, HL activity, TG, and body mass index have independent contributions to HDL2 cholesterol levels. We suggest that in FCHL, TG enrichment of HDL particles and enhanced HL activity lead to the reduction of HDL cholesterol and HDL2 cholesterol.

The hormone sensitive lipase gene in familial combined hyperlipidemia and insulin resistance.

BACKGROUND: Insulin resistance in the most common familial dyslipidemia, familial combined hyperlipidemia (FCHL), could be due to variations in the hormone sensitive lipase (HSL) gene. MATERIALS AND METHODS: The coding region of the HSL gene was screened with the single strand conformation polymorphism analysis in probands of 27 FCHL families with 228 members. In addition, the C-60G promoter substitution of the HSL gene was determined by the restriction fragment length polymorphism analysis in these subjects. RESULTS: No variants in the coding region of the HSL gene were found and the allele frequencies of the C-60G promoter substitution and the silent variant (G3138A) in the 3' untranslated region did not differ between 110 control subjects and 27 probands with FCHL. However, in control women the C-60G substitution was associated with high body mass index [30.6 +/- 0.9 kg m(-2) (mean +/- SD) in subjects with the C/G genotype and 24.8 +/- 4.6 in subjects with the C/C genotype, P = 0.012], and in control men with high rates of insulin-stimulated whole body glucose uptake (70.1 +/- 14.7 vs. 56.7 +/- 14.2 micromol kg(-1) min(-1), P = 0.014). In 228 FCHL family members this substitution was associated with high low-density lipoprotein cholesterol levels in men (4.51 +/- 1.12 vs. 5.17 +/- 1.28 mmol L(-1), P = 0.049), but not in women. CONCLUSIONS: The HSL gene is not a major gene for FCHL. However, the - 60G allele of this gene may affect body weight, insulin sensitivity and serum cholesterol levels.

Changes in paraoxonase and apolipoprotein A-I, B, C-III and E in subjects with combined familiar hyperlipoproteinemia treated with ciprofibrate.

The aim of our study was to determine whether, in patients with familiar combined hyperlipoproteinemia (FCH), ciprofibrate produces changes in paraoxonase, which acts as an antioxidant. A further aim was to estimate changes in serum levels of apolipoproteins, especially in apolipoprotein (apo) A-I and apoC-III. One of the mechanisms of action of fibrates is the activation apo A-I biosynthesis and the inhibition of apoC-III production. It is performed in the liver through peroxisome proliferator activated receptor (PPAR)-alpha activity. We found that ciprofibrate administration enhanced production of apoA-I and paraoxonase transport capacity. Decreases in paraoxonase during ciprofibrate treatment were not statistically significant but increases in serum levels of apoA-I were statistically significant. Levels of apoC-III were decreased, which suggests that ciprofibrate belongs in the group of fibrates that influences lipoprotein metabolism through PPAR-alpha activity.

G-250A substitution in promoter of hepatic lipase gene is associated with dyslipidemia and insulin resistance in healthy control subjects and in members of families with familial combined hyperlipidemia.

Low activity of hepatic lipase (HL) has been associated with high levels of triglycerides and high density lipoproteins, but the association of the HL promoter variants with insulin sensitivity has not been investigated. Therefore, in this study, the relationship of the G-250A promoter variant of the HL gene to the rates of insulin-stimulated glucose uptake measured by the hyperinsulinemic euglycemic clamp was investigated in 110 control subjects (82 men and 28 women, aged 50.7+/-7.6 [mean+/-SD] years, body mass index 26. 1+/-3.6 kg/m(2)) and in 105 first-degree relatives (65 men and 40 women, aged 47.8+/-16.0 years, body mass index 26.9+/-5.3 kg/m(2)) of 34 families with familial combined hyperlipidemia (FCHL). The A-250 allele of the HL promoter was associated with low rates of insulin-stimulated whole-body nonoxidative glucose disposal in control subjects (41.1+/-12.7 micromol. kg(-1). min(-1) in subjects with the G-250G genotype, 36.9+/-13.1 micromol. kg(-1). min(-1) in subjects with the G-250A genotype, and 29.9+/-13.5 micromol. kg(-1). min(-1) in subjects with the A-250A genotype; P=0.012 adjusted for age and sex) and with low rates of insulin-stimulated whole-body glucose oxidation in FCHL family members (16.7+/-4.2 versus 15.0+/-4. 4 versus 14.1+/-4.4 micromol. kg(-1). min(-1), P=0.024). In addition, the A-250 allele was associated with high levels of fasting insulin (P=0.047), very low density lipoprotein cholesterol (P=0.007), and total (P=0.009) and very low density lipoprotein (P=0.005) triglycerides in control subjects and with high levels of low density lipoprotein triglycerides (P=0.001) in FCHL family members (n=340). We conclude that the G-250A promoter variant of the HL gene is associated with dyslipidemia and insulin resistance. Mechanisms via which this polymorphism could affect insulin sensitivity remain to be elucidated.

Contribution of the hepatic lipase gene to the atherogenic lipoprotein phenotype in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCH) is a common genetic lipid disorder with a frequency of 1-2% in the population. In addition to the hypercholesterolemia and/or hypertriglyceridemia that affected individuals exhibit, small, dense LDL particles and decreased HDL-cholesterol levels are traits frequently associated with FCH. Recently, we reported that families with FCH and families enriched for coronary artery disease (CAD) share genetic determinants for the atherogenic lipoprotein phenotype (ALP), a profile presenting with small, dense LDL particles, decreased HDL-cholesterol levels, and increased triglyceride levels. Other studies in normolipidemic populations have shown that the hepatic lipase (HL) gene is linked to HDL-cholesterol levels and that a polymorphism within the HL promoter (-514C-->T) is associated with increased HDL-cholesterol levels as well as larger, more buoyant LDL particles. In the present study, we tested whether the HL gene locus also contributes to ALP in a series of Dutch FCH families using nonparametric sibpair linkage analysis and association analysis. Evidence for linkage of LDL particle size (P < 0.019), HDL-cholesterol (P < 0.003), and triglyceride levels (P < 0.026) to the HL gene locus was observed. A genome scan in a subset of these families exhibited evidence for linkage of PPD (LOD = 2.2) and HDL-cholesterol levels (LOD = 1.2) to the HL gene locus as well. The -514C-->T promoter polymorphism was significantly associated (P < 0.0001) with higher HDL-cholesterol levels in the unrelated males of this population, but not in unrelated females. No association was observed between the polymorphism and LDL particle size or triglyceride levels. Our results provide support that ALP is a multigenic trait and suggest that the relationship between small, dense LDL particles, HDL-cholesterol, and triglyceride levels in FCH families is due, in part, to common genetic factors.

Mutations of the human hepatic lipase gene in patients with combined hypertriglyceridemia/hyperalphalipoproteinemia and in patients with familial combined hyperlipidemia.

Hepatic lipase is an enzyme which hydrolyzes triglycerides from plasma lipoproteins and thus takes part in the metabolism of intermediate density lipoproteins and high-density lipoproteins. The search described here concentrated on mutations of the HL gene in 129 patients with combined hypertriglyceridemia/hyperalphalipoproteinemia and in 184 members of 19 families with familial combined hyperlipidemia. Controls were 100 subjects with favorable lipid values (age 46-51 years). Mutation screening and analysis were performed by temperature-gradient gel electrophoresis, allele-specific restriction genotyping, and sequencing. Six different missense mutations and four different silent mutations were found in the HL gene. The alleles Phe-267 and Gln-343 were detected only once in the patient group with hypertriglyceridemia and hyperalphalipoproteinemia and were not detected in the control group. The allele Met-383 was rare in both patients and controls. We found 9.3% of the patients and only 3.0% of controls to be carrying the Val-73-Met missense mutation. The allele Phe-334 was found in 5.43% of patients and in 2.0% of controls. The difference between the frequencies of these alleles was significant between male patients and male controls (Met-73 P=0.044; Phe-334 P=0.047). Also, the summarized odds ratio of 3.28 (95% confidence interval 1.23-8.73) demonstrates that mutation carriers are significantly more prevalent in the patients. Fifteen carriers of the Met-73 allele were found in six families of the familial combined hyperlipidemia group. Furthermore, six carriers of the Phe-334 allele were found in three families of the same group. In comparison to the controls the summarized odds ratio of 2.45 (95% confidence interval 0.89-6.71) barely missed the level of significance. The linkage between genotype and phenotype was incomplete. These results show an association of the missense mutations Val-73-Met and Leu-334-Phe as susceptibility alleles for combined forms of hyperlipidemia.

Linkage of a candidate gene locus to familial combined hyperlipidemia: lecithin:cholesterol acyltransferase on 16q.

Familial combined hyperlipidemia (FCHL) is a common lipid disorder characterized by elevated levels of plasma cholesterol and triglycerides that is present in 10% to 20% of patients with premature coronary artery disease. To study the pathophysiological basis and genetics of FCHL, we previously reported recruitment of 18 large families. We now report linkage studies of 14 candidate genes selected for their potential involvement in the aspects of lipid and lipoprotein metabolism that are altered in FCHL. We used highly polymorphic markers linked to the candidate genes, and these markers were analyzed using several complementary, nonparametric statistical allele-sharing linkage methodologies. This current sample has been extended over the one in which we identified an association with the apolipoprotein (apo) AI-CIII-AIV gene cluster. We observed evidence for linkage of this region and FCHL (P<0.001), providing additional support for its involvement in FCHL. We also identified a new locus showing significant evidence of linkage to the disorder: the lecithin:cholesterol acyltransferase (LCAT) locus (P<0.0006) on chromosome 16. In addition, analysis of the manganese superoxide dismutase locus on chromosome 6 revealed a suggestive linkage result in this sample (P<0.006). Quantitative traits related to FCHL also provided some evidence of linkage to these regions. No evidence of linkage to the lipoprotein lipase gene, the microsomal triglyceride transfer protein gene, or several other genes involved in lipid metabolism was observed. The data suggest that the lecithin:cholesterol acyltransferase and apolipoprotein AI-CIII-AIV loci may act as modifying genes contributing to the expression of FCHL.

Novel genes for familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) is a complex genetic disorder of unknown etiology. Recently, 'modifier' genes of the FCHL phenotype, such as the apolipoprotein AI-CIII-AIV gene cluster and LPL, have been identified in several populations. A 'major' gene for FCHL has been identified in a Finnish isolate which maps to a region syntenic to murine chromosome 3 where a locus for combined hyperlipidemia has been identified. We review these and other recent studies which indicate that FCHL is genetically heterogeneous.

Evidence against alterations in Lecithin:cholesterol acyltransferase (LCAT) activity in familial combined hyperlipidemia.

Elevated concentrations of plasma cholesterol and triglycerides are characteristic of familial combined hyperlipidemia (FCHL) which may also present with reduced high density lipoprotein (HDL) cholesterol concentrations. Lecithin:cholesterol acyltransferase (LCAT) plays a key role in reverse cholesterol transport by converting unesterified cholesterol to cholesterol ester in the process of maturation of HDL in the presence of its activator, apolipoprotein (apo) A-I. We hypothesised that alterations in LCAT activity or plasma concentrations or gene sequence of apo A-I could influence HDL metabolism in these patients. We studied cholesterol concentrations of high density lipoprotein subfractions and LCAT activity in 25 FCHL subjects and 48 controls. Total HDL (p=0.018) and HDL2 (p=0.008) were significantly decreased in the FCHL group compared with controls. After analyses with adjusted data only HDL2 remained significantly decreased in the FCHL group (p=0.050). The LDLc/HDLc and A-I/HDLc ratios were significantly elevated in the FCHL group (p <0.0001), the latter suggesting the existence of compositional differences in the HDL particles of the FCHL individuals. LCAT activity assessed in the FCHL (19.94+/-3.95 nmol/ml per h) and control (20.13+/-6.86 nmol/ml per h) groups showed no statistically significant differences. A significant positive correlation of LCAT activity with total HDL (r=0.42), HDL3 cholesterol (r=0.46) and apolipoprotein A-I (r=0.47) was observed in affected subjects but not in controls. An association between a Ga(-75)-A variation in the promoter region of the apo A-I gene and elevated concentrations of apo A-I (p=0.009) and apo C-III (p=0.041) was observed. This association was strongly influenced by the status of the subject providing further evidence for a regulatory role of this genetic region in the expression of FCHL. Our data suggests that LCAT activity is normal in FCHL and, therefore, does not account for the abnormalities observed in these patients essentially with regard to the HDL2 subfraction.

Adipose tissue lipoprotein lipase and hormone-sensitive lipase. Contrasting findings in familial combined hyperlipidemia and insulin resistance syndrome.

The metabolism of free fatty acids (FFA) is altered in two common atherosclerosis-promoting disorders: familial combined hyperlipidemia (FCHL) and insulin resistance syndrome (IRS). It has been suggested that these two conditions may have a common etiology. The enzymes lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) are rate-limiting steps for the turnover of fatty acids in adipose tissue, because they hydrolyze extracellular triglycerides in lipoproteins (LPL) and intracellular triglycerides in adipocytes (HSL). The present study was undertaken to simultaneously determine the activities of LPL and HSL in subcutaneous adipose tissue from male patients with FCHL and IRS. LPL and HSL activity was investigated in 10 nonobese FCHL patients and compared with 10 matched healthy nonobese subjects, and in 8 essentially normolipidemic IRS patients (who did not have overt diabetes mellitus) and compared with 9 nonobese matched control subjects. LPL activity was 43% lower in patients with IRS (P < .0005), as compared with control subjects, but HSL activity was not significantly different in the two groups, On the other hand, HSL activity was decreased by 45% in FCHL patients (P < .01), as compared with control subjects, but LPL activity was not significantly different in FCHL patients and the control group. In conclusion, triglyceride metabolism in adipose tissue is altered in both FCHL and IRS. However, the abnormalities observed involve impaired function of LPL in IRS and impaired function of HSL in FCHL, suggesting separate etiologies for the altered lipolysis in these conditions, at least in male subjects.

Absence of cholesteryl ester transfer protein-mediated cholesteryl ester mass transfer from high-density lipoprotein to low-density lipoprotein particles is a major feature of combined hyperlipidaemia.

Elevated plasma cholesteryl ester transfer protein (CETP) mass is characteristic of combined hyperlipidaemia (CHL), an atherogenic dyslipidaemia characterized by increased levels of both very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) and subnormal levels of high-density lipoprotein (HDL). CETP remodels plasma lipoproteins by promoting the heteroexchange of neutral lipids. To determine the mechanism of the CETP-mediated redistribution of cholesteryl ester (CE) between plasma lipoprotein particles in CHL, we measured CE mass transfer and exchange from HDL to apoB-containing lipoproteins under physiological conditions in the plasmas of 14 CHL patients and compared the data with those in a group of normolipidaemic subjects (NLS; n = 9). The rate of CE mass transfer from HDL to VLDL was significantly increased in CHL patients (24.1 +/- 3.8 micrograms CE transferred h-1 mL-1 plasma) when compared with NLS (14.4 +/- 2.6 micrograms CE transferred h-1 mL-1 plasma, P = 0.0001). By contrast with control subjects, no net CE mass transfer from HDL to LDL was detected in CHL patients; transfer of radiolabelled CE to LDL was, however, observed, suggesting the occurrence of CE exchange between HDL and LDL in the absence of net CE mass transfer. The LDL fraction from CHL patients displayed a significant reduction (15%; P < 0.003) in its ability to accept cholesteryl ester from HDL when compared with normolipidaemic LDL. Moreover, a reduction of 10% (P < 0.02) was found in the capacity of hyperlipidaemic HDL to donate cholesteryl esters to apoB-containing lipoproteins as compared with control HDL; the reduced levels (-32%) of HDL2b particles in CHL plasmas may account for this effect. We conclude that the low affinity of hyperlipidaemic LDL particles for CETP, taken together with the elevated plasma concentrations of a qualitatively active CE acceptor, VLDL, and the low HDL levels in CHL patients, result in the absence of net CE mass transfer from HDL to LDL in Combined hyperlipidaemia.

The lipoprotein lipase (Asn291-->Ser) mutation is associated with elevated lipid levels in families with familial combined hyperlipidaemia.

Familial combined hyperlipidaemia (FCHL) is one of the major genetic causes of coronary heart disease (CHD) and is characterised by elevated levels of plasma cholesterol and/or triglycerides in individuals within a single family. Decreased lipoprotein lipase (LPL) activity has been found in some cases of FCHL. A recent study revealed a common mutation in the LPL gene, LPL(Asn291-->Ser), with a frequency of 9.3% in Dutch FCHL patients (Reymer et al,. Circulation, 90 (1994) I-998). This mutation was found in 3 out of 17 FCHL families. Extensive family studies were subsequently performed to determine the effect of this mutation on the phenotypic expression of FCHL. Using a pedigree-based maximum likelihood estimate, we demonstrated that the LPL(Asn291-->Ser) mutation significantly affects the levels of plasma and very low density lipoprotein (VLDL) triglycerides (2.03 +/- 0.21 vs. 1.14 +/- 0.13 and 1.21 +/- 0.16 vs. 0.62 +/- 0.09 mmol/l, carriers and non-carriers, respectively) and VLDL- and high density lipoprotein (HDL) cholesterol (0.83 +/- 0.10 vs. 0.38 +/- 0.06 and 1.02 +/- 0.08 vs. 1.29 +/- 0.05 mmol l, carriers and non-carriers, respectively), but not those of plasma and low density lipoprotein (LDL) cholesterol. These findings indicate that the LPL(Asn291-->Ser) mutation is associated with elevated lipid levels, indicating it may be one of the genetic factors predisposing to FCHL in the families studied.