Mariëtte J.V. Hoffer

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.

Apolipoprotein E1-Hammersmith (Lys146 → Asn;Arg147 → Trp), due to a dinucleotide substitution, is associated with early manifestation of dominant type III hyperlipoproteinaemia

Apolipoprotein E (apoE) is one of the major protein constituents of chylomicron and very low density lipoprotein (VLDL) remnants and plays a central role as a ligand in the receptor-mediated uptake of these particles by the liver. Here we describe a new variant of apoE, apoE1-Hammersmith, which is associated with dominantly expressed type III hyperlipidaemia. The propositus, aged 26, developed tubero-eruptive xanthomas at the age of 3, her daughter developed similar lesions at age 7 but her son, aged 3, shows no clinical abnormality so far. All three cases had an apoE3E1 phenotype and a broad beta band on lipoprotein electrophoresis. Cysteamine modification resulted in a shift of apoE1 to the apoE2 isoform position, indicating that the mutation leading to apoE1-Hammersmith occurred on an apoE3 background. ApoE genotyping confirmed these results. Sequence analysis of DNA of the propositus was performed for exons 3 and 4 and revealed a dinucleotide substitution causing two amino acid changes at adjacent positions (Lys146-->Asn) and (Arg147-->Trp).

An acceptor splice site mutation in intron 16 of the low density lipoprotein receptor gene leads to an elongated, internalization defective receptor

In this report, we describe the characterization of a mutation in the low density lipoprotein (LDL) receptor gene of a true homozygous familial hypercholesterolemic (FH) patient. The combined use of denaturing gradient gel electrophoresis (DGGE) and DNA sequence analysis revealed a unique A to G transition in the penultimate 3-nucleotide of intron 16 of the LDL receptor gene, which disrupts the acceptor splice site. cDNA sequence analysis indicated that a cryptic splice site was activated in intron 16, upstream from the original splice site, leading to the inclusion of 62 nucleotides and a reading frame-shift. The resulting new translation product contains a stretch of 154 amino acids at the carboxy-terminal that have no resemblance to the normal receptor protein. To elucidate the biological effects of the mutation, the structural and functional properties of the mutated LDL receptor protein were studied. Immunoprecipitation of the newly synthesized LDL receptors showed that an aberrant precursor form of the LDL receptor protein was synthesized, about 10 kDa larger than normal, which is not further processed to the mature form. Some 50% of the normal LDL binding activity was found on the cell surface of the patients fibroblasts, whereas internalization and degradation of LDL were abolished.

The V73M mutation in the hepatic lipase gene is associated with elevated cholesterol levels in four Dutch pedigrees with familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) is a heritable lipid disorder characterized by multiple lipoprotein phenotypes within a single family. Previously, we have shown an increased incidence of mutations in the LPL gene which was associated with elevated levels of very low density lipoprotein (VLDL) and decreased levels of high density lipoprotein among the families studied. Now, we report the results of our study on the hepatic lipase gene. We found the HL V73M variant to be present in four FCHL families. By means of a pedigree-based maximum log-likelihood method we analyzed the effect of this variant on the lipid levels in these families. Carriers of the HL V73M variant revealed significantly higher levels of total cholesterol (P < 0.01) and apoB (P <0.01). These findings show that the HL V73M mutant explains another part of the variability in the phenotype observed among FCHL family members, compared with mutations in the LPL gene. Family analysis shows that in these FCHL families, carriers of mutations in the LPL or HL genes have an increased risk for FCHL compared with their non-carrier relatives.

Effect of insulin resistance, apoE2 allele, and smoking on combined hyperlipidemia.

Combined hyperlipidemia may result from the interaction of several metabolic and environmental factors. We explored to what extent fasting insulin concentration, apolipoprotein (apo) E2 frequency, and cigarette smoking explained the serum levels of triglyceride and high-density lipoprotein cholesterol (HDL-C) in patients with combined hyperlipidemia. Forty-nine untreated patients with combined hyperlipidemia were compared with 49 hypercholesterolemic patients who were matched for gender, age, and body mass index. All laboratory values were obtained after 9 weeks of standardized dietary intake and after an overnight fast. The patients with combined hyperlipidemia had a significantly higher (33 pmol/L, 50%) mean insulin concentration than matched hypercholesterolemic control subjects, indicating that the combined hyperlipidemic patients were more insulin resistant. However, the differences in the fasting insulin and triglyceride concentrations within the pairs were only slightly correlated (adjusted r = .29). The combined hyperlipidemic patients were also characterized by a higher frequency of apoE2 alleles (25% versus 6%) and smokers (41% versus 16%). In a matched multiple linear regression model, the differences in insulin concentration, apoE2 allele frequency, and smoking explained 12%, 8%, and 9%, respectively, of the mean paired difference in triglyceride concentration. The differences in insulin concentration or apoE2 allele frequency did not significantly explain the mean paired difference in HDL-C concentration, whereas smoking explained 17% of the difference. In conclusion, fasting insulin concentration, the presence of the apoE2 allele, and smoking may explain 30% of the hypertriglyceridemia and the low levels of HDL-C in nonobese patients with combined hyperlipidemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of apolipoprotein E and insulin resistance on VLDL particles in combined hyperlipidemic patients

Apolipoprotein (apo) E2 and high insulin levels are associated with the severity of hypertriglyceridemia in patients with combined hyperlipidemia. To study how these determinants affect very low-density lipoprotein (VLDL) in combined hyperlipidemic patients, we characterized VLDL particles in 106 unrelated patients with combined hyperlipidemia. The study was performed after 9 weeks of standardized dietary intake and after an overnight fast. Patients heterozygous for apoE2 had significantly higher mean levels of VLDL cholesterol by 0.71 mmol/l (95% CI, 0.30 to 1.12 mmol/l, P < 0.005) and VLDL triglycerides by 0.88 mmol/l, (95% CI, 0.30 to 1.47 mmol/l, P < 0.005) compared to patients without apoE2. The VLDL triglyceride content per particle and the calculated diameter of the VLDL particles were similar in both groups, which indicate a higher number of circulating VLDL particles in heterozygous apoE2 carriers. Patients with high fasting insulin levels (> or = 80 pmol/l) had a higher mean serum VLDL triglyceride level by 0.56 mmol/l (95% CI, 0.04 to 1.07 mmol/l, P < 0.05). The calculated VLDL diameter was larger by 3.7 nm (95% CI, 1.2 to 6.2 nm, P < 0.005) and the particles contained more triglycerides by 2.7 weight percent (95% CI, 0.3 to 5.1 weight percent, P < 0.05). These insulin-dependent changes in VLDL particles were only present in the absence of apoE2. In conclusion, patients heterozygous for apoE2 have higher numbers of circulating VLDL particles, whereas patients with high fasting insulin levels have larger, triglyceride enriched VLDL particles.

Economic evaluation of multiplex ligation-dependent probe amplification and karyotyping in prenatal diagnosis: a cost-minimization analysis

PurposeTo assess the cost-effectiveness of Multiplex Ligation-dependent Probe Amplification (MLPA, P095 kit) compared to karyotyping.MethodsA cost-minimization analysis alongside a nationwide prospective clinical study of 4,585 women undergoing amniocentesis on behalf of their age (≥36xa0years), an increased risk following first trimester prenatal screening or parental anxiety.ResultsDiagnostic accuracy of MLPA (P095 kit) was comparable to karyotyping (1.0 95% CI 0.999–1.0). Health-related quality of life did not differ between the strategies (summary physical health: mean difference 0.31, pxa0=xa00.82; summary mental health: mean difference 1.91, pxa0=xa00.22). Short-term costs were lower for MLPA: mean difference €315.68 (bootstrap 95% CI €315.63–315.74; −44.4%). The long-term costs were slightly higher for MLPA: mean difference €76.42 (bootstrap 95% CI €71.32–81.52; +8.6%). Total costs were on average €240.13 (bootstrap 95% CI €235.02–245.23; −14.9%) lower in favor of MLPA. Cost differences were sensitive to proportion of terminated pregnancies, sample throughput, individual choice and performance of tests in one laboratory, but not to failure rate or the exclusion of polluted samples.ConclusionFrom an economic perspective, MLPA is the preferred prenatal diagnostic strategy in women who undergo amniocentesis on behalf of their age, following prenatal screening or parental anxiety.

Is Hypertriglyceridemia always a Risk Factor

The concept that hypertriglyceridemia is a risk factor for CHD has been disputed by epidemiological data that showed that an elevated plasma triglyceride concentration is not an independent risk factor of CHD. However, more insight in the heterogeneity of triglyceride-rich lipoproteins and the increased knowledge of lipoprotein metabolism have contributed to the growing notion that accumulation of cholesterol-rich VLDL and chylomicron remnants constitutes an atherogenic risk. An elevated plasma triglyceride concentration associated with obesity, low HDL-cholesterol concentration, dense small LDL particles, insulin resistance and prolonged postprandial lipemia bears a high risk of CHD. In the present chapter, we review the metabolic derangements of triglyceride-rich lipoproteins in hypertriglyceridemia. Endogenous hypertriglyceridemia is a multifactorial disease. Genetic as well as exogenous factors predispose subjects to the development of the characteristic lipoprotein abnormalities. Mutations in the LPL- and apoC-lll gene are important genetic factors, whereas increased amounts of visceral fat and insulin resistance are principal exogenous factors that contribute to the expression of hypertriglyceridemia. Several studies have demonstrated that overproduction of triglycerides and an impaired catabolism contribute to the hypertriglyceridemia. An increased supply of glucose and free fatty acids contributes to overproduction of very low density lipoproteins, thereby increasing the burden of triglyceride-rich lipoproteins on the common lipolytic pathway at the level of lipoprotein lipase. Low lipoprotein lipase activity and increased amounts of lipolysis- inhibiting free fatty acids further impair lipolysis. When dietary measures and hypoglycemic agents have failed to achieve acceptable lipid levels, lipid- lowering drugs should be advised. Fibric acids are the drugs of choice because of their significant improvement of lipid, lipoprotein and fibrinogen levels.