Sybil Charriere

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

BACKGROUND & AIMSnNon-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.nnnMETHODSnWe 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.nnnRESULTSnABL 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.nnnCONCLUSIONSnOur 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.

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

BACKGROUNDnTwo 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.nnnMETHODSnWe 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.nnnRESULTSnThe -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).nnnCONCLUSIONnThese 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.

Autoantibodies against GPIHBP1 as a Cause of Hypertriglyceridemia

BACKGROUND A protein that is expressed on capillary endothelial cells, called GPIHBP1 (glycosylphosphatidylinositol‐anchored high‐density lipoprotein binding protein 1), binds lipoprotein lipase and shuttles it to its site of action in the capillary lumen. A deficiency in GPIHBP1 prevents lipoprotein lipase from reaching the capillary lumen. Patients with GPIHBP1 deficiency have low plasma levels of lipoprotein lipase, impaired intravascular hydrolysis of triglycerides, and severe hypertriglyceridemia (chylomicronemia). During the characterization of a monoclonal antibody–based immunoassay for GPIHBP1, we encountered two plasma samples (both from patients with chylomicronemia) that contained an interfering substance that made it impossible to measure GPIHBP1. That finding raised the possibility that those samples might contain GPIHBP1 autoantibodies. METHODS Using a combination of immunoassays, Western blot analyses, and immunocytochemical studies, we tested the two plasma samples (as well as samples from other patients with chylomicronemia) for the presence of GPIHBP1 autoantibodies. We also tested the ability of GPIHBP1 autoantibodies to block the binding of lipoprotein lipase to GPIHBP1. RESULTS We identified GPIHBP1 autoantibodies in six patients with chylomicronemia and found that these autoantibodies blocked the binding of lipoprotein lipase to GPIHBP1. As in patients with GPIHBP1 deficiency, those with GPIHBP1 autoantibodies had low plasma levels of lipoprotein lipase. Three of the six patients had systemic lupus erythematosus. One of these patients who had GPIHBP1 autoantibodies delivered a baby with plasma containing maternal GPIHBP1 autoantibodies; the infant had severe but transient chylomicronemia. Two of the patients with chylomicronemia and GPIHBP1 autoantibodies had a response to treatment with immunosuppressive agents. CONCLUSIONS In six patients with chylomicronemia, GPIHBP1 autoantibodies blocked the ability of GPIHBP1 to bind and transport lipoprotein lipase, thereby interfering with lipoprotein lipase–mediated processing of triglyceride‐rich lipoproteins and causing severe hypertriglyceridemia. (Funded by the National Heart, Lung, and Blood Institute and the Leducq Foundation.)

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 (nu200a=u200a26, ru200a=u200a0.88). 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.

Consensus statement on the management of dyslipidaemias in adults

Working group commissioned by the the French Society of Endocrinology (SFE) Francophone Society of Diabetes (SFD), The New French Society of Atherosclerosis (NSFA), S. Béliard a, F. Bonnet b, B. Bouhanick c, E. Bruckert d, B. Cariou e, S. Charrière f, V. Durlach g, P. Moulin f,∗, R. Valéro a, B. Vergès g,h a Service de nutrition, maladies métaboliques, endocrinologie, hôpital de la Conception, CHU de Marseille, AP–HM, 13009 Marseille, France b Service d’endocrinologie-diabétologie, Inserm U1018, université Rennes 1, CHU de Rennes, Rennes, France c Pôle CVM, service d’HTA et thérapeutique, CHU Rangueil, université de Toulouse 3, 331059 Toulouse, France d Service d’endocrinologie, hôpital Pitié Salpêtrière, Paris, France e Inserm UMR 1087, clinique d’endocrinologie, Institut du thorax, université de Nantes, CHU de Nantes, 44000 Nantes, France f Fédération d’endocrinologie, GHE, HCL, université de Lyon 1, Inserm UMR 1060 CARMEN, 60003 Lyon, France g Pôle thoracique cardiovasculaire et neurologique, hôpital Robert-Debré, 51092 Reims, France h Service d’endocrinologie, diabétologie et maladies métaboliques, CHU de dijon, INSERM LNC UMR 866, Université Bourgogne Franche-Conté, 21000 Dijon, France

Establishment of reference values of α-tocopherol in plasma, red blood cells and adipose tissue in healthy children to improve the management of chylomicron retention disease, a rare genetic hypocholesterolemia

BackgroundChylomicron retention disease (CMRD), a rare genetic hypocholesterolemia, results in neuro-ophtalmologic damages, which can be prevented by high doses of vitamin E during infancy. In these patients, plasma vitamin E concentration is significantly reduced due to defects of chylomicron secretion. Vitamin E in adipose tissue (AT) and red blood cells (RBC) have been proposed as potential relevant biomarkers of vitamin E status but no reference values in children are available. The objectives were (i) to establish age-reference intervals in healthy children for α-tocopherol in plasma, red blood cells (RBC) and adipose tissue (AT) and (ii) to determine the variations of α-tocopherol in patients with CMRD after oral treatment with vitamin E.MethodsThis prospective study included 166 healthy children (1xa0month - 18xa0years) and 4 patients with CMRD. Blood and AT were collected in healthy children during a scheduled surgery and in patients before and after a 4-month treatment with α-tocopherol acetate.ResultsThe reference ranges for α-tocopherol were 11.9 - 30xa0μmol/L in plasma, 2.0 - 7.8xa0μmol/L packed cells in RBC and 60 - 573xa0nmol/g in AT. α-tocopherol levels in plasma correlated with those of RBC (ru2009=u20090.31; pu2009<u20090.01).In patients with CMRD after 4xa0months treatment, α-tocopherol concentrations remained less than 70xa0% of the control values in plasma, increased by 180xa0% to reach normal values in RBC, and remained stable in the normal range in AT.ConclusionThis study establishes pediatric reference intervals for α-tocopherol in plasma, RBC and AT. These values will be beneficial in assessing accurate α-tocopherol status in children and to optimize the monitoring of rare diseases such as CMRD. Our data suggest that RBC α-tocopherol, appears as a relevant biomarker to appreciate the effectiveness of treatment with α-tocopherol in patients with a rare primary hypocholesterolemia. The biopsy of AT could be used at diagnosis to assess the severity of the vitamin E deficiency and periodically after a long duration of vitamin E therapy to assess whether the treatment is effective, based on reference intervals defined in this study.