No evidence of accelerated atherosclerosis in a 66-yr-old chylomicronemia patient homozygous for the nonsense mutation (Tyr61-->stop) in the lipoprotein lipase gene

Homozygous familial lipoprotein lipase deficiency without obvious coronary artery stenosis

The prevalence of familial lipoprotein lipase deficiency (LPLD) is approximately one in 1,000,000 in the general population. There are conflicting reports on whether or not LPLD is atherogenic. We conducted coronary computed tomographic (CT) angiography on two patients in their 70 s who had genetically confirmed LPLD. Patient 1 was a 73 year old woman with a body mass index (BMI) of 27.5 kg/m², no history of diabetes mellitus and no history of drinking alcohol or smoking. At the time of her first visit, her serum total cholesterol, triglycerides and high-density lipoprotein cholesterol levels were 4.8 mmol/L, 17.3 mmol/L, and 0.5 mmol/L, respectively. She was treated with a lipid-restricted diet and fibrate but her serum TG levels remained extremely high. Next-generation sequencing analysis revealed a missense mutation (homo) in the LPL gene, c.662T>C (p. Ile221Thr), leading to the diagnosis of homozygous familial LPL deficiency (LPLD). Patient 2 was another 73- year- old woman. She also had marked hypertriglyceridemia with no history of diabetes mellitus, drinking alcohol, or smoking. Previous genetic studies showed she had a nonsense mutation (homozygous) in the LPL gene, c.1277G>A (p.Trp409Ter). To clarify the degree of coronary artery stenosis in these two cases, we conducted coronary CT angiography and found that no coronary artery stenosis in either the right or left coronary arteries. Based on the findings in these two elderly women along with previous reports on patients in their 60 s with LPLD and hypertriglyceridemia, we suggest that LPLD may not be associated with the development or progression of coronary artery disease.

Serum HDL-C values: An extremely useful marker for differentiating homozygous lipoprotein lipase deficiency from severe hypertriglyceridemia with other causes in Japan: A meta-analysis based on literatures on Japanese homozygous lipoprotein lipase deficiency

BACKGROUNDS AND AIM

Lipoprotein lipase (LPL) deficiency is a genetic disorder with a defective gene for lipoprotein lipase, leading to very high triglycerides. In the daily practice it is much more common to come across severely hypertriglyceridemia without homozygous or compound heterozygous LPL deficiency (SHTG).

METHODS

We investigated on how to screen homozygous or compound heterozygous LPL deficiency using lipid parameters by meta-analyzing past 20 subjects on this genetic disease reported by Japanese investigators. As a comparison with LPL deficiency, 21 subjects with SHTG from recent two studies were included in this study.

RESULTS

Serum HDL-C levels were significantly lower in LPL deficiency than in SHTG (0.38 ± 0.13 vs 0.94 ± 0.28 mmol/L (mean ± SD), p < 0.001), whereas other serum lipids did not differ between the two groups. The ROC curve ± standard error for serum HDL-C for discriminating the two groups was 0.97 ± 0.019. Sensitivity and specificity for distinguishing the two groups were 90% and 95%, respectively when serum HDL-C 0.62 mmol/L was adopted as cut point.

CONCLUSION

We found for the first time that serum HDL-C is an extremely useful marker for discriminating LPL deficiency from SHTG in Japanese population.

Current Diagnosis and Management of Primary Chylomicronemia

Primary chylomicronemia (PCM) is a rare and intractable disease characterized by marked accumulation of chylomicrons in plasma. The levels of plasma triglycerides (TGs) typically range from 1,000 - 15,000 mg/dL or higher.

PCM is caused by defects in the lipoprotein lipase (LPL) pathway due to genetic mutations, autoantibodies, or unidentified causes. The monogenic type is typically inherited as an autosomal recessive trait with loss-of-function mutations in LPL pathway genes ( LPL , LMF1 , GPIHBP1 , APOC2 , and APOA5 ). Secondary/environmental factors (diabetes, alcohol intake, pregnancy, etc.) often exacerbate hypertriglyceridemia (HTG).

The signs, symptoms, and complications of chylomicronemia include eruptive xanthomas, lipemia retinalis, hepatosplenomegaly, and acute pancreatitis with onset as early as in infancy. Acute pancreatitis can be fatal and recurrent episodes of abdominal pain may lead to dietary fat intolerance and failure to thrive.

The main goal of treatment is to prevent acute pancreatitis by reducing plasma TG levels to at least less than 500-1,000 mg/dL. However, current TG-lowering medications are generally ineffective for PCM. The only other treatment options are modulation of secondary/environmental factors. Most patients need strict dietary fat restriction, which is often difficult to maintain and likely affects their quality of life.

Timely diagnosis is critical for the best prognosis with currently available management, but PCM is often misdiagnosed and undertreated. The aim of this review is firstly to summarize the pathogenesis, signs, symptoms, diagnosis, and management of PCM, and secondly to propose simple diagnostic criteria that can be readily translated into general clinical practice to improve the diagnostic rate of PCM. In fact, these criteria are currently used to define eligibility to receive social support from the Japanese government for PCM as a rare and intractable disease.

Nevertheless, further research to unravel the molecular pathogenesis and develop effective therapeutic modalities is warranted. Nationwide registry research on PCM is currently ongoing in Japan with the aim of better understanding the disease burden as well as the unmet needs of this life-threatening disease with poor therapeutic options.

Atherosclerosis Regression and Cholesterol Efflux in Hypertriglyceridemic Mice

[Figure: see text].

Identification of a novel LPL nonsense variant and further insights into the complex etiology and expression of hypertriglyceridemia-induced acute pancreatitis

Background

Hypertriglyceridemia (HTG) is a leading cause of acute pancreatitis. HTG can be caused by either primary (genetic) or secondary etiological factors, and there is increasing appreciation of the interplay between the two kinds of factors in causing severe HTG.

Objectives

The main aim of this study was to identify the genetic basis of hypertriglyceridemia-induced acute pancreatitis (HTG-AP) in a Chinese family with three affected members (the proband, his mother and older sister).

Methods

The entire coding and flanking sequences of LPL, APOC2, APOA5, GPIHBP1 and LMF1 genes were analyzed by Sanger sequencing. The newly identified LPL nonsense variant was subjected to functional analysis by means of transfection into HEK-293 T cells followed by Western blot and activity assays. Previously reported pathogenic LPL nonsense variants were collated and compared with respect to genotype and phenotype relationship.

Results

We identified a novel nonsense variant, p.Gln118* (c.351C > T), in the LPL gene, which co-segregated with HTG-AP in the Chinese family. We provided in vitro evidence that this variant resulted in a complete functional loss of the affected LPL allele. We highlighted a role of alcohol abuse in modifying the clinical expression of the disease in the proband. Additionally, our survey of 12 previously reported pathogenic LPL nonsense variants (in 20 carriers) revealed that neither serum triglyceride levels nor occurrence of HTG-AP was distinguishable among the three carrier groups, namely, simple homozygotes, compound heterozygotes and simple heterozygotes.

Conclusions

Our findings, taken together, generated new insights into the complex etiology and expression of HTG-AP.

Hypertriglyceridemia and Atherosclerosis: Using Human Research to Guide Mechanistic Studies in Animal Models

Human studies support a strong association between hypertriglyceridemia and atherosclerotic cardiovascular disease (CVD). However, whether a causal relationship exists between hypertriglyceridemia and increased CVD risk is still unclear. One plausible explanation for the difficulty establishing a clear causal role for hypertriglyceridemia in CVD risk is that lipolysis products of triglyceride-rich lipoproteins (TRLs), rather than the TRLs themselves, are the likely mediators of increased CVD risk. This hypothesis is supported by studies of rare mutations in humans resulting in impaired clearance of such lipolysis products (remnant lipoprotein particles; RLPs). Several animal models of hypertriglyceridemia support this hypothesis and have provided additional mechanistic understanding. Mice deficient in lipoprotein lipase (LPL), the major vascular enzyme responsible for TRL lipolysis and generation of RLPs, or its endothelial anchor GPIHBP1, are severely hypertriglyceridemic but develop only minimal atherosclerosis as compared with animal models deficient in apolipoprotein (APO) E, which is required to clear TRLs and RLPs. Likewise, animal models convincingly show that increased clearance of TRLs and RLPs by LPL activation (achieved by inhibition of APOC3, ANGPTL3, or ANGPTL4 action, or increased APOA5) results in protection from atherosclerosis. Mechanistic studies suggest that RLPs are more atherogenic than large TRLs because they more readily enter the artery wall, and because they are enriched in cholesterol relative to triglycerides, which promotes pro-atherogenic effects in lesional cells. Other mechanistic studies show that hepatic receptors (LDLR and LRP1) and APOE are critical for RLP clearance. Thus, studies in animal models have provided additional mechanistic insight and generally agree with the hypothesis that RLPs derived from TRLs are highly atherogenic whereas hypertriglyceridemia due to accumulation of very large TRLs in plasma is not markedly atherogenic in the absence of TRL lipolysis products.

Molecular and functional characterization of familial chylomicronemia syndrome

BACKGROUND AND AIMS

Familial chylomicronemia syndrome is a rare autosomal recessive disorder leading to severe hypertriglyceridemia (HTG) due to mutations in lipoprotein lipase (LPL)-associated genes. Few data exist on the clinical features of the disorder or on comprehensive genetic approaches to uncover the causative genes and mutations.

METHODS

Eight patients diagnosed with familial hyperchylomicronemia with recessive inheritance were included in this study (two males and six females; median age of onset 23.0 years; mean triglyceride level 3446 mg/dl). We evaluated their clinical features, including coronary artery disease using coronary computed tomography, and performed targeted next-generation sequencing on a panel comprising 4813 genes associated with known clinical phenotypes. After standard filtering for allele frequency <1% and in silico annotation prediction, we used three types of variant filtering to identify causative mutations: homozygous mutations in known familial hyperchylomicronemia-associated genes, homozygous mutations with high damaging scores in novel genes, and deleterious mutations within 37 genes known to be associated with HTG.

RESULTS

A total of 1810 variants out of the 73,389 identified with 94.3% mean coverage (×20) were rare and nonsynonymous. Among these, our schema detected four pathogenic or likely pathogenic mutations in the LPL gene (p.Ala248LeufsTer4, p.Arg270Cys, p.Ala361Thr, and p.Val227Gly), including one novel mutation and a variant of uncertain significance. Patients harboring LPL gene mutations showed no severe atherosclerotic changes in the coronary arteries, but recurrent pancreatitis with long-term exposure to HTG was observed.

CONCLUSIONS

These results demonstrate that LPL gene plays a major role in extreme HTG associated with hyperchylomicronemia, although the condition may not cause severe atherosclerosis.

Severe hypertriglyceridemia in Japan: Differences in causes and therapeutic responses

BACKGROUND

Severe hypertriglyceridemia (>1000 mg/dL) has a variety of causes and frequently leads to life-threating acute pancreatitis. However, the origins of this disorder are unclear for many patients.

OBJECTIVE

We aimed to characterize the causes of and responses to therapy in rare cases of severe hypertriglyceridemia in a group of Japanese patients.

METHODS

We enrolled 121 patients from a series of case studies that spanned 30 years. Subjects were divided into 3 groups: (1) primary (genetic causes); (2) secondary (acquired); and (3) disorders of uncertain causes. In the last group, we focused on 3 possible risks factors for hypertriglyceridemia: obesity, diabetes mellitus, and heavy alcohol intake.

RESULTS

Group A (n = 20) included 13 patients with familial lipoprotein lipase deficiency, 3 patients with apolipoprotein CII deficiency, and other genetic disorders in the rest of the group. Group B patients (n = 15) had various metabolic and endocrine diseases. In Group C (uncertain causes; n = 86), there was conspicuous gender imbalance (79 males, 3 females) and most male subjects were heavy alcohol drinkers. In addition, 18 of 105 adult patients (17%) had histories of acute pancreatitis.

CONCLUSION

The cause of severe hypertriglyceridemia is uncertain in many patients. In primary genetic forms of severe hypertriglyceridemia, genetic diversity between populations is unknown. In the acquired forms, we found fewer cases of estrogen-induced hypertriglyceridemia than in Western countries. In our clinical experience, the cause of most hypertriglyceridemia is uncertain. Our work suggests that genetic factors for plasma triglyceride sensitivity to alcohol should be explored.

Method for estimating high sdLDL-C by measuring triglyceride and apolipoprotein B levels

Background

We previously developed an assay to directly measure small dense (sd) low-density lipoprotein cholesterol (LDL-C) levels, which is not widely used in general clinical practice. Therefore, we propose a simpler method, “LDL window,” that uses conventional methods for estimating high sdLDL-C levels.

Methods

We analyzed our previous studies (2006–2008) on healthy subjects and patients with type 2 diabetes and coronary artery disease (CAD). The sdLDL-C level was measured using the precipitation method, and LDL size was determined using gradient gel electrophoresis. The “LDL window” comprises the estimation of LDL particle number and size. We adopted apolipoprotein B (apoB) for the estimation of the LDL particle number and used 110 mg/dL as the cutoff value for hyper-apoB. Triglycerides (TGs) are a powerful inverse determinant of LDL particle size. Therefore, we adopted TG for the estimation of the LDL particle size and used 150 mg/dL as the cutoff value for hyper-TG. Subjects were stratified into the following four subgroups: normal, hyper-TG, hyper-apoB, and hyper-TG/-apoB. Non-high-density lipoprotein cholesterol (non-HDL-C) is a surrogate marker for apoB; therefore, the “alternative LDL window” comprised non-HDL-C (cutoff, 170 mg/dL) and TG.

Results

The top quartile (Q4) of sdLDL-C (>31 mg/dL) doubled in patients with diabetes and CAD. The hyper-TG/-apoB group in the “LDL window” represented >90% Q4 and <4% Q1 and Q2, irrespective of the subjects. The sdLDL-C levels in the hyper-TG/-apoB group were 50% higher in patients with diabetes and CAD than those in controls. Similar results were obtained using the “alternative LDL window.”

Conclusions

Our proposed “LDL window” may help identify patients at high risk of CAD independent of LDL-C.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-017-0417-6) contains supplementary material, which is available to authorized users.

Loss of Transcription Factor CREBH Accelerates Diet-Induced Atherosclerosis in Ldlr-/- Mice

OBJECTIVE

Liver-enriched transcription factor cAMP-responsive element-binding protein H (CREBH) regulates plasma triglyceride clearance by inducing lipoprotein lipase cofactors, such as apolipoprotein A-IV (apoA-IV), apoA-V, and apoC-II. CREBH also regulates apoA-I transcription. This study aims to determine whether CREBH has a role in lipoprotein metabolism and development of atherosclerosis.

APPROACH AND RESULTS

CREBH-deficient Creb3l3(-/-) mice were bred with Ldlr(-/-) mice creating Ldlr(-/-) Creb3l3(-/-) double knockout mice. Mice were fed on a high-fat and high-sucrose Western diet for 20 weeks. We showed that CREBH deletion in Ldlr(-/-) mice increased very low-density lipoprotein-associated triglyceride and cholesterol levels, consistent with the impairment of lipoprotein lipase-mediated triglyceride clearance in these mice. In contrast, high-density lipoprotein cholesterol levels were decreased in CREBH-deficient mice, which was associated with decreased production of apoA-I from the liver. The results indicate that CREBH directly activated Apoa1 gene transcription. Accompanied by the worsened atherogenic lipid profile, Ldlr(-/-) Creb3l3(-/-) mice developed significantly more atherosclerotic lesions in the aortas than Ldlr(-/-) mice.

CONCLUSIONS

We identified CREBH as an important regulator of lipoprotein metabolism and suggest that increasing hepatic CREBH activity may be a novel strategy for prevention and treatment of atherosclerosis.

Lipoprotein Lipase Deficiency (R243H) in a Type 2 Diabetes Patient with Multiple Arterial Aneurysms

Lipoprotein lipase (LPL) deficiency is a rare monogenic disorder that manifests as severe hypertriglyceridemia. Whether or not LPL deficiency accelerates the development of atherosclerosis remains controversial. We herein report a 66-year-old woman who was homozygous for the R243H LPL mutation. She had developed multiple arterial aneurysms and systemic atherosclerosis despite good control of other atherogenic risk factors, including diabetes. Furthermore, although intensive pharmaceutical therapies had been minimally effective, medium chain triglyceride (MCT) therapy reduced the serum triglyceride levels. Thus, this case suggests important role that mutated LPL protein plays in the progression of atherosclerosis and that MCT therapy is potentially effective, even for severe hypertriglyceridemia due to LPL deficiency.

Lipoprotein lipase and atherosclerosis

Lipoprotein lipase has long been known to hydrolyse triglycerides from triglycerides-rich lipoproteins. More recently, it has been shown to promote the binding of lipoproteins to various lipoprotein receptors. Evidence is also presented regarding the possible atherogenic role of lipoprotein lipase. In theory, lipoprotein lipase deficiency should help to clarify this question. However, the rarity of this condition means that it has not been possible to conduct epidemiological studies. An alternative approach is to investigate the correlation of lipoprotein lipase with onset of cardiovascular disease in prospective studies in large population-based cohorts. Complementary with this approach, animal models have been used to explore the atherogenicity of lipoprotein lipase expressed by macrophages.

Regulating intestinal function to reduce atherogenic lipoproteins

Significant knowledge regarding different molecules involved in the transport of dietary fat into the circulation has been garnered. Studies point to the possibility that accumulation of intestine-derived lipoproteins in the plasma could contribute to atherosclerosis. This article provides a brief overview of dietary lipid metabolism and studies in mice supporting the hypothesis that intestinal lipoproteins contribute to atherosclerosis. Deficiencies in lipoprotein lipase and Gpihbp1, and overexpression of heparanse in mice, are associated with increases in atherosclerosis, suggesting that defects in catabolism of larger lipoproteins in the plasma contribute to atherosclerosis. Furthermore, inositol-requiring enzyme 1β-deficient mice that produce more intestinal lipoproteins also develop more atherosclerosis. Thus, increases in plasma intestinal lipoproteins due to either overproduction or reduced catabolism result in augmented atherosclerosis. Intestinal lipoproteins tend to adhere strongly to subendothelial proteoglycans, elicit an inflammatory response by endothelial cells and activate macrophages, contributing to the initiation and progression of the disease. Thus, molecules that reduce intestinal lipid absorption can be useful in lowering atherosclerosis.

A 60-y-old chylomicronemia patient homozygous for missense mutation (G188E) in the lipoprotein lipase gene showed no accelerated atherosclerosis

BACKGROUND

Familial lipoprotein lipase (LPL) deficiency is a rare autosomal recessive disorder caused by mutations in the LPL gene. Patients with LPL deficiency have chylomicronemia; however, whether they develop accelerated atherosclerosis remains unclear.

METHODS

We investigated clinical and mutational characteristics of a 60-y-old Japanese patient with chylomicronemia.

RESULTS

The patient's fasting plasma triglyceride levels were >9.0 mmol/l. In postheparin plasma, one fifth of the normal LPL protein mass was present; however, LPL activity was undetectable. Molecular analysis of the LPL gene showed the patient to be a homozygote of missense mutation replacing glycine with glutamine at codon 188 (G188E), which had been known to produce mutant LPL protein lacking lipolytic activity. Ultrasonographic examination of the patient's carotid and femoral arteries showed no accelerated atherosclerosis. Moreover, 64-slice mechanical multidetector-row computer tomography (MDCT) angiography did not detect any accelerated atherosclerotic lesions in the patient's coronary arteries. The patient had none of the risk factors such as smoking, hypertension, and diabetes.

CONCLUSIONS

Our case suggests that accelerated atherosclerosis may not develop in patients with LPL deficiency, when they have no risk factors.

Expression of LPL in Endothelial-Intact Artery Results in Lipid Deposition and Vascular Cell Adhesion Molecule-1 Upregulation in Both LPL and ApoE-Deficient Mice

Objective— Overexpression of lipoprotein lipase (LPL) in deendothelialized artery led to profound localized lipid deposition. In this study the role of LPL in atherogenesis in endothelial-intact carotid arteries was assessed in genetically hyperlipidemic LPL- and ApoE-deficient mice.

Methods and Results— Human wild-type LPL (hLPLwt), catalytically inactive LPL (hLPL194), or control alkaline phosphatase (hAP) were expressed in endothelial-intact carotid arteries via adenoviral vectors. Compared with Ad-hAP, lipid deposition in the arterial wall increased 10.0- and 5.1-fold for Ad-hLPLwt and Ad-hLPL194 in LPL-deficient mice, and 10.6- and 6.2-fold in ApoE-deficient mice, respectively. Vascular cell adhesion molecule-1 (VCAM-1) was upregulated in Ad-hLPLwt and Ad-hLPL194 transferred arteries.

Conclusions— Endothelial cell associated LPL, either active or inactive, in the arterial wall is a strong proatherosclerotic factor in both LPL- and ApoE-deficient mice.

A novel nonsense mutation in the LPL gene in a Chinese neonate with hypertriglyceridemia

BACKGROUND

Lipoprotein lipase (LPL) deficiency is a rare autosomal recessive disorder characterized by hypertriglyceridemia. The genetic defect lies in a mutation of the LPL gene.

METHODS

A Chinese neonate with non-consanguineous parents was incidentally found to have hypertriglyceridemia. Mutation in her LPL gene was screened by using polymerase chain reaction and direct DNA sequencing.

RESULTS

Homozygous missense mutations (L252V) were detected in the LPL gene of the patient. A novel nonsense mutation (C27X) was also identified.

CONCLUSION

Our finding supports L252V mutation in the LPL gene is a common mutation in Chinese with familial hyperchylomicronemia syndrome. DNA-based diagnosis in this syndrome is definitive. It saves the need for heparin-infusion test, which carries the risk of hemorrhage, and the measurement of LPL activity, which is tedious and is not widely available.

Serum lipoprotein lipase concentration and risk for future coronary artery disease: the EPIC-Norfolk prospective population study

BACKGROUND

Lipoprotein lipase (LPL) is associated with coronary artery disease (CAD) risk, but prospective population data are lacking. This is mainly because of the need for cumbersome heparin injections, which are necessary for LPL measurements. Recent retrospective studies, however, indicate that LPL concentration can be reliably measured in serum that enabled evaluation of the prospective association between LPL and future CAD.

METHODS AND RESULTS

LPL concentration was determined in serum samples of men and women in the EPIC-Norfolk population cohort who developed fatal or nonfatal CAD during 7 years of follow-up. For each case (n=1006), 2 controls, matched for age, sex, and enrollment time, were identified. Serum LPL concentration was lower in cases compared with controls (median and interquartile range: 61 [43-85] versus 66 [46-92] ng/mL; P<0.0001). Those in the highest LPL concentration quartile had a 34% lower risk for future CAD compared with those in the lowest quartile (odds ratio [OR] 0.66; confidence interval [CI], 0.53 to 0.83; P<0.0001). This effect remained significant after adjustment for blood pressure, diabetes, smoking, body mass index, and low-density lipoprotein (LDL) cholesterol (OR, 0.77; CI, 0.60-0.99; P=0.02). As expected from LPL biology, additional adjustments for either high-density lipoprotein cholesterol (HDL-C) or triglyceride (TG) levels rendered loss of statistical significance. Of interest, serum LPL concentration was positively linear correlated with HDL and LDL size.

CONCLUSIONS

Reduced levels of serum LPL are associated with an increased risk for future CAD. The data suggest that high LPL concentrations may be atheroprotective through decreasing TG levels and increasing HDL-C levels.

Effects of diacylglycerol administration on serum triacylglycerol in a patient homozygous for complete lipoprotein lipase deletion

We investigated postprandial and long-term effects of dietary diacylglycerol (DAG) on serum triacylglycerol (TAG) levels in a 34-year-old man homozygous for complete lipoprotein lipase deletion (LPL deletion). In study 1, Three different oils (DAG, TAG, or medium-chain fatty acid TAG [MCT]) were ingested to examine differences in the postprandial serum TAG response. Postprandial serum TAG levels after DAG oil ingestion were lower than those after TAG oil ingestion and similar to those after MCT oil ingestion. In study 2, the patient was allowed to ingest ordinary cooking oil for 2 months and then DAG oil (containing 80% DAG; target, 20 g/d) for the next 3 months. During the test period, serum TAG levels were measured and dietary evaluations were performed every month. The patient was provided with dietary instruction and consultation at each clinical visit. Serum TAG levels were 1939 to 2525 mg/dL when he used ordinary cooking oil, 1926 to 1173 mg/dL when he used ordinary cooking oil together with DAG oil, and 749 mg/dL when he used DAG oil alone. The TAG intake decreased from 86.9 to 43.0 g and the DAG intake increased from 0.9 to 12.4 g during the study period. Subsequently, 45 g DAG oil (equivalent to 36 g DAG) per day was consumed, and the serum TAG level increased to 2195 mg/dL. Although there was a positive correlation between the TAG intake and serum TAG levels during the period of DAG oil use (P < .01, y = 33.7x - 583.1), there was no such correlation between DAG oil intake and serum TAG levels. These results suggested that substitution of 12.0 g/d DAG (equivalent to 15 g DAG oil) for TAG oil had the same effect as reducing TAG oil consumption for controlling the serum TAG levels in an LPL-depleted patient with hypertriglyceridemia. In conclusion, the results of study 1 and study 2 demonstrate that DAG oil might be replaced by MCT oil as cooking oil for those with LPL deletion.

A novel and simple method for quantification of small, dense LDL

A preponderance of small, dense (sd) LDL is strongly associated with the development of coronary heart disease, but the method for the measurement of sd LDL is too laborious for clinical use. We report a simple method for the quantification of sd LDL that is applicable to an autoanalyzer. This method consists of two steps: first, to precipitate the lipoprotein of density (d) <1.044 g/ml using heparin-magnesium; and second, to measure LDL-cholesterol in the supernatant by the homogeneous method or apolipoprotein B (apoB) by an immunoturbidometric assay. The cholesterol and apoB values obtained by the precipitation method (45 +/- 26 and 33 +/- 20 mg/dl, respectively) were similar to those obtained in the lipoprotein (d = 1.044-1.063) separated by ultracentrifugation (42 +/- 22 and 31 +/- 17 mg/dl, respectively), and there was an excellent correlation between the two methods for sd LDL-cholesterol (y = 1.05X + 1, r = 0.88, n = 69) and apoB (y = 1.07X, r = 0.90). Sd LDL values had a significant inverse correlation with LDL size. A high correlation was found between sd LDL-cholesterol and apoB values (r = 0.94). Sd LDL value was related to triglyceride, apoB, and LDL-cholesterol, but not to the buoyant LDL level. These results suggest that this precipitation method is a simple and rapid method for the measurement of sd LDL concentration.

Novel LPL mutation (L303F) found in a patient associated with coronary artery disease and severe systemic atherosclerosis

BACKGROUND

Patients with lipoprotein lipase (LPL) deficiency had been generally thought to be spared accelerated atherosclerosis in spite of a marked elevation of plasma triglyceride levels. However, it has been recently reported that some heterozygous and homozygous LPL-deficient patients are associated with premature atherosclerosis. In this paper, we report a 55-year-old type I hyperlipidaemic patient with a novel missense mutation in the LPL gene.

PATIENT AND RESULTS

The patient had suffered from coronary artery disease, abdominal aortic aneurysm, and stenoses of the bilateral renal arteries and superficial femoral arteries. Sequencing of the genomic DNA revealed that the patient was a homozygote for the mutation, a G to C transition at nucleotide position 1069 in the exon 6, resulting in an amino acid substitution of Phe for Leu303 (L303F). Approximately 6% and approximately 40% of normal LPL activity and LPL mass, respectively, were detected in the patient's postheparin plasma. An in vitro expression study demonstrated that COS7 cells transfected with L303F mutant cDNA produced a 40% amount of LPL protein in cell lysates compared with normal cDNA, but no protein was detected in the media. Lipoprotein lipase activity was completely absent in both lysates and media of the cells transfected with the mutant cDNA, suggesting that this mutation in the LPL gene results in the production of a functionally inactive protein.

CONCLUSION

This case suggests that the LPL missense mutation (L303F), which impairs lipolysis but preserves the LPL mass, is proatherogenic.