Efficacy of two vitamin E formulations in patients with abetalipoproteinemia and chylomicron retention disease.

Abetalipoproteinemia (ABL) and chylomicron retention disease (CMRD) are extremely rare recessive forms of hypobetalipoproteinemia characterized by intestinal lipid malabsorption and severe vitamin E deficiency. Vitamin E is often supplemented in the form of fat-soluble vitamin E acetate, but fat malabsorption considerably limits correction of the deficiency. In this crossover study, we administered two different forms of vitamin E, tocofersolan (a water-soluble derivative of RRR-α-tocopherol) and α-tocopherol acetate, to three patients with ABL and four patients with CMRD. The aims of this study were to evaluate the intestinal absorption characteristics of tocofersolan versus α-tocopherol acetate by measuring the plasma concentrations of α-tocopherol over time after a single oral load and to compare efficacy by evaluating the ability of each formulation to restore vitamin E storage after 4 months of treatment. In patients with ABL, tocofersolan and α-tocopherol acetate bioavailabilities were extremely low (2.8% and 3.1%, respectively). In contrast, bioavailabilities were higher in patients with CMRD (tocofersolan, 24.7%; α-tocopherol acetate, 11.4%). Plasma concentrations of α-tocopherol at 4 months were not significantly different by formulation type in ABL or CMRD. This study provides new insights about vitamin E status in ABL and CMRD and suggests the potential of different formulations as treatment options.

An APOA5 3' UTR variant associated with plasma triglycerides triggers APOA5 downregulation by creating a functional miR-485-5p binding site.

APOA5 c.*158C>T (rs2266788), located in the 3' UTR, belongs to APOA5 haplotype 2 (APOA5*2), which is strongly associated with plasma triglyceride levels and modulates the occurrence of both moderate and severe hypertriglyceridemia. Individuals with APOA5*2 display reduced APOA5 expression at the posttranscriptional level. However, the functionality of this haplotype remains unclear. We hypothesized that the hypertriglyceridemic effects of APOA5*2 could involve miRNA regulation in the APOA5 3' UTR. Bioinformatic studies have identified the creation of a potential miRNA binding site for liver-expressed miR-485-5p (MIRN485-5p) in the mutant APOA5 3' UTR with the c.*158C allele. In human embryonic kidney 293T (HEK293T) cells cotransfected with an APOA5 3' UTR luciferase reporter vector and a miR485-5p precursor, c.*158C allele expression was significantly decreased. Moreover, in HuH-7 cells endogenously expressing miR-485-5p, we observed that luciferase activity was significantly lower in the presence of the c.*158C allele than in the presence of the c.*158T allele, which was completely reversed by a miR-485-5p inhibitor. We demonstrated that the rare c.*158C APOA5 allele creates a functional target site for liver-expressed miR-485-5p. Therefore, we propose that the well-documented hypertriglyceridemic effect of APOA5*2 involves an APOA5 posttranscriptional downregulation mediated by miR-485-5p.

Lipid profile and cardiovascular risk factors in pediatric liver transplant recipients.

Cardiovascular diseases induce long-term morbidity and mortality of adult LT recipients. The aim of this retrospective study was to assess CVRF, lipid abnormalities, and atherosclerosis (appraised by c-IMT), more than 10 yr after pediatric LT. Thirty-one children who underwent LT between December 1990 and December 2000 were included. Median age at LT was 14 months (range 4-64), and median follow-up after LT was 11.9 yr (range 9.0-17.3). In our cohort, obesity (9.7%) and treated hypertension (9.7%) were rare. None of the patients was smoker or diabetic. High TC and TG were both observed in 6.5% of the patients. The mean c-IMT for male patients was 1.22 ± 1.55 and 1.58 ± 1.23 mm in female patients. Seven patients (22%) had a mean c-IMT above +2 s.d. Values below the 5th percentile were noted for LDL-cholesterol (58.1%), HDL-cholesterol (25.8%), apolipoprotein B (40%), and apolipoprotein A1 (20%). LDL-cholesterol and apolipoprotein B levels were significantly lower in patients treated by tacrolimus in comparison with CsA (p < 0.05). In conclusion, our results suggest that pediatric LT patients do not present significant CVRF; moreover, instead of hyperlipidemia, hypocholesterolemia (LDL-C) is frequent and immunosuppressive therapy is probably the cause.

Homozygous MTTP and APOB mutations may lead to hepatic steatosis and fibrosis despite metabolic differences in congenital hypocholesterolemia.

BACKGROUND & AIMS: Non-alcoholic steatohepatitis leading to fibrosis occurs in patients with abetalipoproteinemia (ABL) and homozygous or compound heterozygous familial hypobetalipoproteinemia (Ho-FHBL). We wanted to establish if liver alterations were more frequent in one of both diseases and were influenced by comorbidities. METHODS: We report genetic, clinical, histological and biological characteristics of new cases of ABL (n =7) and Ho-FHBL (n = 7), and compare them with all published ABL (51) and Ho-FHBL (22) probands. RESULTS: ABL patients, diagnosed during infancy, presented mainly with diarrhea, neurological and ophthalmological impairments and remained lean, whereas Ho-FHBL were diagnosed later, with milder symptoms often becoming overweight in adulthood. Despite subtle differences in lipid phenotype, liver steatosis was observed in both groups with a high prevalence of severe fibrosis (5/27 for Ho-FHBL vs. 4/58 for ABL (n.s.)). Serum triglycerides concentration was higher in Ho-FHBL whereas total and HDL-cholesterol were similar in both groups. In Ho-FHBL liver alterations were found to be independent from the apoB truncation size and apoB concentrations. CONCLUSIONS: Our findings provide evidence for major liver abnormalities in both diseases. While ABL and Ho-FHBL patients have subtle differences in lipid phenotype, carriers of APOB mutations are more frequently obese. These results raise the question of a complex causal link between apoB metabolism and obesity. They suggest that the genetic defect in VLDL assembly is critical for the occurrence of liver steatosis leading to fibrosis and shows that obesity and insulin resistance might contribute by increasing lipogenesis.

Inhibitory effects of in vivo oxidized high-density lipoproteins on platelet aggregation: evidence from patients with abetalipoproteinemia.

There is evidence that high-density lipoproteins (HDLs) may regulate platelet function, but disparate results exist regarding the effects of oxidized HDLs on platelets. The objective of our study was to determine the role of in vivo oxidized HDLs on platelet aggregation. Platelet aggregation and redox status were investigated in 5 patients with abetalipoproteinemia (ABLP) or homozygous hypobetalipoproteinemia, two rare metabolic diseases characterized by the absence of apolipoprotein B-containing lipoproteins, compared to 5 control subjects. Platelets isolated from plasma of patients with ABLP aggregated 4 to 10 times more than control platelets, depending on the agonist. By contrast, no differences in the extent of platelet aggregation were observed between ABLP platelet-rich plasma (PRP) and control PRP, suggesting the presence of a protective factor in ABLP plasma. ABLP HDLs inhibited agonist-induced platelet aggregation by binding to SR-BI, while control HDLs had no effect. On the other hand, lipoprotein-deficient plasma from patients with ABLP did not inhibit platelet aggregation. Severe oxidative stress was evidenced in patients with ABLP. Compared to control HDLs, ABLP HDLs showed a 40% decrease of α-tocopherol and an 11-fold increased malondialdehyde concentration. These results demonstrate that in vivo oxidized HDLs do not lose their antiaggregatory properties despite oxidation.

Molecular and functional analysis of two new MTTP gene mutations in an atypical case of abetalipoproteinemia.

Abetalipoproteinemia (ABL) is an inherited disease characterized by the defective assembly and secretion of apolipoprotein B-containing lipoproteins caused by mutations in the microsomal triglyceride transfer protein large subunit (MTP) gene (MTTP). We report here a female patient with an unusual clinical and biochemical ABL phenotype. She presented with severe liver injury, low levels of LDL-cholesterol, and subnormal levels of vitamin E, but only mild fat malabsorption and no retinitis pigmentosa or acanthocytosis. Our objective was to search for MTTP mutations and to determine the relationship between the genotype and this particular phenotype. The subject exhibited compound heterozygosity for two novel MTTP mutations: one missense mutation (p.Leu435His) and an intronic deletion (c.619-5_619-2del). COS-1 cells expressing the missense mutant protein exhibited negligible levels of MTP activity. In contrast, the minigene splicing reporter assay showed an incomplete splicing defect of the intronic deletion, with 26% of the normal splicing being maintained in the transfected HeLa cells. The small amount of MTP activity resulting from the residual normal splicing in the patient explains the atypical phenotype observed. Our investigation provides an example of a functional analysis of unclassified variations, which is an absolute necessity for the molecular diagnosis of atypical ABL cases.

Chylomicron retention disease: report of two cases from a Greek Island.

Chylomicron retention disease (CRD), or Anderson disease, is a rare, hereditary cause of fat malabsorption. It is one of the familial hypocholesterolaemia syndromes, along with homozygous hypobetalipoproteinaemia (HBL) and abetalipoproteinaemia (ABL). We report clinical, laboratory and histological data as well as molecular DNA analysis in the case of a 4-month-old boy with failure to thrive and steatorrhea who was diagnosed with CRD. His mother's first cousin, who was diagnosed as hypobetalipoproteinaemia 30 years ago, was also reviewed and his diagnosis was revised to CRD. Both patients were treated with a low fat diet and supplementation with fat-soluble vitamins resulting in significant improvement. In conclusion, CRD is a well-defined cause of fat malabsorption and can be distinguished from other forms of familial hypocholesterolaemia because of its specific lipid profile.

A severe form of abetalipoproteinemia caused by new splicing mutations of microsomal triglyceride transfer protein (MTTP).

Abetalipoproteinemia is a rare autosomal recessive disease characterized by low lipid levels and by the absence of apoB-containing lipoproteins. It is the consequence of microsomal triglyceride transfer protein (MTTP) deficiency. We report two patients with new MTTP mutations. We studied their functional consequences on the triglyceride transfer function using duodenal biopsies. We transfected MTTP mutants in HepG2 and HeLa cells to investigate their association with protein disulfide isomerase (PDI) and their localization at the endoplasmic reticulum. These children have a severe abetalipoproteinemia. Both of them had also a mild hypogammaglobulinemia. They are compound heterozygotes with c.619G>T and c.1237-28A>G mutations within the MTTP gene. mRNA analysis revealed abnormal splicing with deletion of exon 6 and 10, respectively. Deletion of exon 6 (Δ6-MTTP) introduced a frame shift in the reading frame and a premature stop codon at position 234. Despite the fact that Δ6-MTTP and Δ10-MTTP mutants were not capable of binding PDI, both MTTP mutant proteins normally localize at the endoplasmic reticulum. However, these two mutations induce a loss of MTTP triglyceride transfer activity. These two mutations lead to abnormal truncated MTTP proteins, incapable of binding PDI and responsible for the loss of function of MTTP, thereby explaining the severe abetalipoproteinemia phenotype of these children.

Molecular spectrum of autosomal dominant hypercholesterolemia in France.

Autosomal Dominant Hypercholesterolemia (ADH), characterized by isolated elevation of plasmatic LDL cholesterol and premature cardiovascular complications, is associated with mutations in 3 major genes: LDLR (LDL receptor), APOB (apolipoprotein B) and PCSK9(proprotein convertase subtilisin-kexin type 9). Through the French ADH Research Network, we collected molecular data from 1358 French probands from eleven different regions in France.Mutations in the LDLR gene were identified in 1003 subjects representing 391 unique events with 46.0% missense, 14.6% frameshift, 13.6% splice, and 11.3% nonsense mutations, 9.7% major rearrangements, 3.8% small in frame deletions/insertions, and 1.0% UTR mutations. Interestingly,175 are novel mutational events and represent 45% of the unique events we identified, highlighting a specificity of the LDLR mutation spectrum in France. Furthermore, mutations in the APOB gene were identified in 89 probands and in the PCSK9 gene in 10 probands. Comparison of available clinical and biochemical data showed a gradient of severity for ADH-causing mutations:FH=PCSK9>FDB>«Others¼ genes. The respective contribution of each known gene to ADH inthis French cohort is: LDLR 73.9%, APOB 6.6%, PCSK9 0.7%. Finally, in 19.0% of the probands,no mutation was found, thus underscoring the existence of ADH mutations located in still unknown genes.

A controlled study of consumption of beta-glucan-enriched soups for 2 months by type 2 diabetic free-living subjects.

Type 2 diabetes is associated with a higher cardiovascular risk and there has been a growing interest in using dietary intervention to improve lipid profile and glucose control. The present work aims at analysing the effects of the enrichment of a normal diet with beta-glucan (3.5 g/d) in free-living type 2 diabetic subjects for 2 months, using a palatable soup. This trial was a parallel, placebo-controlled, double-blinded randomised study performed in fifty-three type 2 diabetic subjects. During a 3-week run-in period, subjects daily consumed a ready meal control soup (without beta-glucan). For the following 8 weeks, subjects were randomly assigned to consume daily either a control soup or a beta-glucan soup. Changes in lipid profile (total cholesterol (TC), HDL- and LDL-cholesterol (HDLc and LDLc), apo B and TAG) and in glucose control (HbA1c and fasting glucose) were measured. There was no significant alteration in lipid profile in the two groups (TC, HDLc, LDLc and apo B). TAG decreased significantly in the beta-glucan group compared with the control group ( - 0.12 (SD 0.38) v. 0.12 (SD 0.44) mmol/l, P = 0.03). HbA1c and fasting glucose were not reduced in any group. A single daily ingestion of 3.5 g beta-glucan, as required by official dietary recommendations, for 8 weeks did not change the lipid profile and HbA1c in type 2 diabetic subjects. To improve the metabolic profile of type 2 diabetic subjects in the long term, the quantity, the food vectors and the tolerability of beta-glucan products may be re-evaluated.

Chylomicron retention disease: a long term study of two cohorts.

Lipoprotein assembly is critical for the intestinal absorption of dietary lipids and of fat-soluble vitamins. Through their inhibition of chylomicron secretion, mutations of the Sar1B gene coding for Sar1 GTPase are associated with chylomicron retention disease (CRD). The aim of this study was to describe the phenotypic expression of CRD in two clinically and genetically well characterized cohorts, and to compare their long term evolution. The study in 7 children from France (X age 11.3+/-1.7 years) and 9 from Quebec, Canada (X age 12+/-2.5 years) involved data collection from medical records for growth evaluation, neurological and ophthalmological status as well as bone density over an average follow-up period of 4.9 years for the French cohort and of 10.6 years for the Canadian one. All CRD patients presented within the first few months of life with diarrhea and failure to thrive. Severe hypocholesterolemia coupled with normal triglycerides was associated with low LDL and HDL-cholesterol, as well as with low apolipoproteins A-I and B. Varying degrees of essential fatty acid and of vitamin E deficiency were observed. The earlier diagnosis in the Canadian cohort (1.3+/-0.04 years) than in the French one (6.3+/-1.3 years) was unrelated with the severity of presenting symptoms. The fact that the disease had more impact on growth and bone density in the latter group may be related to delayed diagnosis of the disease. Vitamin E deficiency led to functional neurological and ophthalmic changes in a small number of patients but only one developed areflexia. Finally, genotype-phenotype correlation is not obvious in our cohort with CRD; even if, the Canadian subjects with the allele 409G>A had a more severe degree (P<0.001) of hypocholesterolemia than the other patients, many clinical data are inconsistent with a hypothetical genotype-phenotype correlation. This study provides new insights on the phenotypic expression of CRD over time and emphasizes the need to screen the lipid profile of infants with chronic diarrhea and failure to thrive.

Identification of two novel mutations and long-term follow-up in abetalipoproteinemia: a report of four cases.

Abetalipoproteinemia (ABL; OMIM 200100) is an inherited disorder resulting from mutations in the microsomal triglyceride transfer protein gene and characterized by a major lipid malabsorption leading to extremely low plasma cholesterol and triglyceride levels and fat-soluble vitamins deficiencies. We report two novel mutations (c.59del17 and c.582C>A) and the long-term follow-up of four ABL subjects treated with vitamin E. The good outcome of the early-treated patients contrasts with severe ataxia and retinopathy observed in the patient with delayed treatment. In conclusion, early diagnosis and early management are essential to prevent the manifestations following the fat-soluble vitamin deficiencies.

Apoa5 Q139X truncation predisposes to late-onset hyperchylomicronemia due to lipoprotein lipase impairment.

While type 1 hyperlipidemia is associated with lipoprotein lipase or apoCII deficiencies, the etiology of type 5 hyperlipidemia remains largely unknown. We explored a new candidate gene, APOA5, for possible causative mutations in a pedigree of late-onset, vertically transmitted hyperchylomicronemia. A heterozygous Q139X mutation in APOA5 was present in both the proband and his affected son but was absent in 200 controls. It was subsequently found in 2 of 140 cases of hyperchylomicronemia. Haplotype analysis suggested the new Q139X as a founder mutation. Family studies showed that 5 of 9 total Q139X carriers had hyperchylomicronemia, 1 patient being homozygote. Severe hypertriglyceridemia in 8 heterozygotes was strictly associated with the presence on the second allele of 1 of 2 previously described triglyceride-raising minor APOA5 haplotypes. Furthermore, ultracentrifugation fraction analysis indicated in carriers an altered association of Apoa5 truncated and WT proteins to lipoproteins, whereas in normal plasma, Apoa5 associated with VLDL and HDL/LDL fractions. APOB100 kinetic studies in 3 severely dyslipidemic patients with Q139X revealed a major impairment of VLDL catabolism. Lipoprotein lipase activity and mass were dramatically reduced in dyslipidemic carriers, leading to severe lipolysis defect. Our observations strongly support in humans a role for APOA5 in lipolysis regulation and in familial hyperchylomicronemia.

Association of APOA5 -1131T>C and S19W gene polymorphisms with both mild hypertriglyceridemia and hyperchylomicronemia in type 2 diabetic patients.

BACKGROUND: Two minor apolipoprotein A5 (APOA5) gene haplotypes, represented by -1131T>C and S19W polymorphisms, are strong determinants of plasma triglyceride (TG) concentration variability across human populations. Hypertriglyceridemia is frequent in type 2 diabetes (T2D) and hyperchylomicronemia is not uncommon. METHODS: We investigated the association of -1131T>C and S19W polymorphisms with diabetic dyslipidemia in 400 Caucasian T2D patients divided in 2 groups: group N with 130 normotriglyceridemics (TG<90th percentile) and group M with 270 moderately hypertriglyceridemics. A third group of 51 diabetic patients (group H) with history of hyperchylomicronemia (TG>15 mM) was also studied. RESULTS: The -1131C allele was more frequent in both mild and severe hypertriglyceridemia (20.6% vs 9.8% vs 5.0%, group H vs M vs N, p<0.001). The 19W allele was more frequent only in patients with hyperchylomicronemia (14.0% vs 6.5% vs 6.1%, group H vs M vs N, p=0.001). In group N+M, the -1131C allele was associated with higher TG (+13%, p=0.034) and lower HDLc (-10%, p=0.004). The 19W allele was only associated with lower HDLc (-9%, p=0.022). CONCLUSION: These results suggest that in T2D APOA5 polymorphisms contribute to modulate dyslipidemia. Both -1131T>C and S19W polymorphisms are associated with hyperchylomicronemia and only -1131T>C polymorphism with mild hypertriglyceridemia.

Homozygous familial hypercholesterolemia in childhood: Genotype-phenotype description, established therapies and perspectives.

Familial hypercholesterolemia (FH) is a co-dominantly inherited disorder of plasma lipoprotein metabolism. The prevalence of heterozygous FH (HeFH) is between 1/500 and 1/200 whereas that of homozygous form (HoFH) is about 1/1,000,000. Diagnosis is based on cutaneous xanthomas and untreated levels of LDL-cholesterol over 500 mg/dl before 10 years of age. Life expectancy, without treatment, does not exceed 20 years of age. The aim of this study is to characterise in details a cohort of 8 HoFH paediatric patients in order to illustrate all the current therapeutic options and to add some clinical and genetic information about this rare disease. We collected demographic, clinical, biological, imaging and genotype details. Furthermore, clinical and biochemical response to different treatment methods was retrospectively evaluated. All patients had genetically proven HoFH. All patients were subject to a lipid-lowering diet and medical treatment (except one), three patients underwent a liver transplant and one an hepatocytes infusion. Medical treatment was well tolerated with a median reduction of 44% and 47% in LDL-Cholesterol and Total Cholesterol respectively. The hepatocytes transplant produced a further, though slight, decrease in cholesterol levels as opposed to medical therapy alone. Transplanted patients normalized their cholesterol levels. Since the very high cardiovascular risk, HoFH requires immediate diagnosis, treatment and monitoring. Nowadays, the use of statins remains the cornerstone of medical therapy and liver transplantation is the possibly curative therapy. Besides, high hopes are pinned in new drugs (antibody targeting PCSK9, Mipomersen and Lomitapide) and stem cells.

Combination of circulating antilipoprotein lipase (Anti-LPL) antibody and heterozygous S172 fsX179 mutation of LPL gene leading to chronic hyperchylomicronemia.

CONTEXT: Sporadic hyperchylomicronemia (type V hyperlipoproteinemia) results from complex interactions between genetic and environmental factors that often remain unknown. DESIGN: Upon investigation of a patient suffering from recurrent hypertriglyceridemic pancreatitis without family history or conventional secondary cause of dyslipidemia, we identified a previously unreported nonsense heterozygous lipoprotein lipase (LPL) gene mutation S172fsX179 associated with an antihuman LPL IgG. RESULTS: This autoantibody partially inhibited wild-type LPL activity in vitro. Furthermore, the patient's plasma triglyceride concentrations were efficiently decreased under immunosuppressive treatment, and this was confirmed by sequential withdrawal/reintroduction tests. CONCLUSIONS: We consider that this unique combination of a genetic defect and an autoimmune disease results in chronic major hypertriglyceridemia. Because immunosuppressive treatment can improve this dyslipidemia, assessment of anti-LPL autoantibody is worthwhile in unmanageable chronic major hypertriglyceridemia, even in the presence of a heterozygous LPL deficiency.

Relation between XbA1 apolipoprotein B gene polymorphism and cardiovascular risk in a type 2 diabetic cohort.

AIM: To evaluate in a prospective study the association of XbA1 apolipoprotein B (apoB) gene polymorphism with lipid parameters and cardiovascular (CV) events in a type 2 diabetic cohort. METHODS AND RESULTS: A cohort of 212 type 2 diabetic patients, free of any cardiovascular complication, was studied. Cardiovascular events were registered for all the patients for 5 years. XbA1 apolipoprotein B gene polymorphism was analysed by PCR-RFLP method. A mild increase in HbA1c was found in X+X+ carriers (P = 0.014). Despite this lower glycemic control, there were no differences between genotype subgroups for lipid parameters except for apoB, significantly higher in X+X+ than in X-X- subjects. In univariate analysis, the cardiovascular events rate was higher in X-X- but did not reach statistical significance (P =0.07). In stepwise multivariate regression analysis, cardiovascular events risk was significantly higher in X- carriers (P = 0.014) and also in smokers, microalbuminuric and older patients. CONCLUSIONS: We report for the first time in a prospective study the association of XbA1 apolipoprotein B gene polymorphism and cardiovascular events in a diabetic population. The mechanism underlying the excess of cardiovascular risk in X- carriers, despite a better metabolic profile, is likely to involve a linkage disequilibrium between apolipoprotein B gene locus and another gene locus related to cardiovascular risk.

Immune response to Abeta-peptides in peripheral blood from patients with Alzheimer's disease and control subjects.

To investigate the immune response to amyloid beta-peptide (Abeta: Abeta40 and Abeta42) in peripheral human blood, sera were obtained from 36 patients with Alzheimer's disease (AD) and 34 age-matched controls. ELISA assays were used to measure antibody concentrations to Abeta-peptides. T cell response was assessed using a lymphoproliferation assay. Both AD and control subjects had low and variable concentrations of antibodies against Abeta (predominantly IgG1). The mean antibody to Abeta concentrations did not differ between groups. No specific T cell response to Abeta-peptides was detected. Natural levels of antibodies to Abeta in peripheral blood are present in all human subjects and are unlikely to be useful in the identification of patients who would respond to potential AD immune therapy. Specific cellular immune responses to Abeta in human blood were not detected.

Post-heparin LPL activity measurement using VLDL as a substrate: a new robust method for routine assessment of plasma triglyceride lipolysis defects.

BACKGROUND: Determination of lipoprotein lipase (LPL) activity is important for hyperchylomicronemia diagnosis, but remains both unreliable and cumbersome with current methods. Consequently by using human VLDL as substrate we developed a new LPL assay which does not require sonication, radioactive or fluorescent particles. METHODS: Post-heparin plasma was added to the VLDL substrate prepared by ultracentrifugation of heat inactivated normolipidemic human serums, diluted in buffer, pH 8.15. Following incubation at 37°c, the NEFA (non esterified fatty acids) produced were assayed hourly for 4 hours. LPL activity was expressed as µmol/l/min after subtraction of hepatic lipase (HL) activity, obtained following LPL inhibition with NaCl 1.5 mmol/l. Molecular analysis of LPL, GPIHBP1, APOA5, APOC2, APOE genes was available for 62 patients. RESULTS: Our method was reproducible (coefficient of variation (CV): intra-assay 5.6%, inter-assay 7.1%), and tightly correlated with the conventional radiolabelled triolein emulsion method (n = 26, r = 0.88). Normal values were established at 34.8 ± 12.8 µmol/l/min (mean ± SD) from 20 control subjects. LPL activities obtained from 71 patients with documented history of major hypertriglyceridemia showed a trimodal distribution. Among the 11 patients with a very low LPL activity (< 10 µmol/l/min), 5 were homozygous or compound heterozygous for LPL or GPIHBP1 deleterious mutations, 3 were compound heterozygous for APOA5 deleterious mutations and the p.S19W APOA5 susceptibility variant, and 2 were free of any mutations in the usual candidate genes. No homozygous gene alteration in LPL, GPIHBP1 and APOC2 genes was found in any of the patients with LPL activity > 10 µmol/l/min. CONCLUSION: This new reproducible method is a valuable tool for routine diagnosis and reliably identifies LPL activity defects.

Post-heparin LPL activity measurement using VLDL as a substrate: a new robust method for routine assessment of plasma triglyceride lipolysis defects.

BACKGROUND: Determination of lipoprotein lipase (LPL) activity is important for hyperchylomicronemia diagnosis, but remains both unreliable and cumbersome with current methods. Consequently by using human VLDL as substrate we developed a new LPL assay which does not require sonication, radioactive or fluorescent particles. METHODS: Post-heparin plasma was added to the VLDL substrate prepared by ultracentrifugation of heat inactivated normolipidemic human serums, diluted in buffer, pH 8.15. Following incubation at 37°c, the NEFA (non esterified fatty acids) produced were assayed hourly for 4 hours. LPL activity was expressed as µmol/l/min after subtraction of hepatic lipase (HL) activity, obtained following LPL inhibition with NaCl 1.5 mmol/l. Molecular analysis of LPL, GPIHBP1, APOA5, APOC2, APOE genes was available for 62 patients. RESULTS: Our method was reproducible (coefficient of variation (CV): intra-assay 5.6%, inter-assay 7.1%), and tightly correlated with the conventional radiolabelled triolein emulsion method (n = 26, r = 0.88). Normal values were established at 34.8 ± 12.8 µmol/l/min (mean ± SD) from 20 control subjects. LPL activities obtained from 71 patients with documented history of major hypertriglyceridemia showed a trimodal distribution. Among the 11 patients with a very low LPL activity (<10 µmol/l/min), 5 were homozygous or compound heterozygous for LPL or GPIHBP1 deleterious mutations, 3 were compound heterozygous for APOA5 deleterious mutations and the p.S19W APOA5 susceptibility variant, and 2 were free of any mutations in the usual candidate genes. No homozygous gene alteration in LPL, GPIHBP1 and APOC2 genes was found in any of the patients with LPL activity >10 µmol/l/min. CONCLUSION: This new reproducible method is a valuable tool for routine diagnosis and reliably identifies LPL activity defects.