Lipoprotein(a): Pathophysiology, measurement, indication and treatment in cardiovascular disease. A consensus statement from the Nouvelle Société Francophone d'Athérosclérose (NSFA).

Lipoprotein(a) is an apolipoprotein B100-containing low-density lipoprotein-like particle that is rich in cholesterol, and is associated with a second major protein, apolipoprotein(a). Apolipoprotein(a) possesses structural similarity to plasminogen but lacks fibrinolytic activity. As a consequence of its composite structure, lipoprotein(a) may: (1) elicit a prothrombotic/antifibrinolytic action favouring clot stability; and (2) enhance atherosclerosis progression via its propensity for retention in the arterial intima, with deposition of its cholesterol load at sites of plaque formation. Equally, lipoprotein(a) may induce inflammation and calcification in the aortic leaflet valve interstitium, leading to calcific aortic valve stenosis. Experimental, epidemiological and genetic evidence support the contention that elevated concentrations of lipoprotein(a) are causally related to atherothrombotic risk and equally to calcific aortic valve stenosis. The plasma concentration of lipoprotein(a) is principally determined by genetic factors, is not influenced by dietary habits, remains essentially constant over the lifetime of a given individual and is the most powerful variable for prediction of lipoprotein(a)-associated cardiovascular risk. However, major interindividual variations (up to 1000-fold) are characteristic of lipoprotein(a) concentrations. In this context, lipoprotein(a) assays, although currently insufficiently standardized, are of considerable interest, not only in stratifying cardiovascular risk, but equally in the clinical follow-up of patients treated with novel lipid-lowering therapies targeted at lipoprotein(a) (e.g. antiapolipoprotein(a) antisense oligonucleotides and small interfering ribonucleic acids) that markedly reduce circulating lipoprotein(a) concentrations. We recommend that lipoprotein(a) be measured once in subjects at high cardiovascular risk with premature coronary heart disease, in familial hypercholesterolaemia, in those with a family history of coronary heart disease and in those with recurrent coronary heart disease despite lipid-lowering treatment. Because of its clinical relevance, the cost of lipoprotein(a) testing should be covered by social security and health authorities.

Guidelines for the diagnosis and management of chylomicron retention disease based on a review of the literature and the experience of two centers.

Familial hypocholesterolemia, namely abetalipoproteinemia, hypobetalipoproteinemia and chylomicron retention disease (CRD), are rare genetic diseases that cause malnutrition, failure to thrive, growth failure and vitamin E deficiency, as well as other complications. Recently, the gene implicated in CRD was identified. The diagnosis is often delayed because symptoms are nonspecific. Treatment and follow-up remain poorly defined.The aim of this paper is to provide guidelines for the diagnosis, treatment and follow-up of children with CRD based on a literature overview and two pediatric centers 'experience.The diagnosis is based on a history of chronic diarrhea with fat malabsorption and abnormal lipid profile. Upper endoscopy and histology reveal fat-laden enterocytes whereas vitamin E deficiency is invariably present. Creatine kinase (CK) is usually elevated and hepatic steatosis is common. Genotyping identifies the Sar1b gene mutation.Treatment should be aimed at preventing potential complications. Vomiting, diarrhea and abdominal distension improve on a low-long chain fat diet. Failure to thrive is one of the most common initial clinical findings. Neurological and ophthalmologic complications in CRD are less severe than in other types of familial hypocholesterolemia. However, the vitamin E deficiency status plays a pivotal role in preventing neurological complications. Essential fatty acid (EFA) deficiency is especially severe early in life. Recently, increased CK levels and cardiomyopathy have been described in addition to muscular manifestations. Poor mineralization and delayed bone maturation do occur. A moderate degree of macrovesicular steatosis is common, but no cases of steatohepatitis cirrhosis. Besides a low-long chain fat diet made up uniquely of polyunsaturated fatty acids, treatment includes fat-soluble vitamin supplements and large amounts of vitamin E. Despite fat malabsorption and the absence of postprandial chylomicrons, the oral route can prevent neurological complications even though serum levels of vitamin E remain chronically low. Dietary counseling is needed not only to monitor fat intake and improve symptoms, but also to maintain sufficient caloric and EFA intake. Despite a better understanding of the pathogenesis of CRD, the diagnosis and management of the disease remain a challenge for clinicians. The clinical guidelines proposed will helpfully lead to an earlier diagnosis and the prevention of complications.

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.

Anderson or chylomicron retention disease: molecular impact of five mutations in the SAR1B gene on the structure and the functionality of Sar1b protein.

Anderson disease (and/or chylomicron retention disease-CMRD) is a rare, autosomic recessive disorder characterized by chronic diarrhea, failure to thrive, and hypocholesterolemia in childhood. The specific molecular defect was identified in 2003 and consists of mutations in the SAR1B gene which encodes for intracellular Sar1b protein. To date, only 8 mutations in six families have been described. We report here 15 new cases of CMRD among 8 families from France and Canada. We identified three unique homozygous mutations of SAR1B gene in French families originated from Turkey, Algeria and Portugal: a stop codon in exon 6 (c.364G>T, p.Glu122X), a whole deletion of exon 2 (c. 1-4482_58+1406 del 5946 ins15bp) and a missense mutation in exon 7 (c.554G>T, p.Gly185Val). The 2 missense mutations found in the 5 French-Canadian families had already been described in the eight previously published mutations: c.409G>A (p.Asp137Asn) and c.537T>A (p.Ser179Arg). In an attempt to explain the functional impairment of mutated proteins, computational analysis and sequence alignment were performed. The nonsense mutation and the whole deletion of exon 2 produced truncated proteins, the missense mutations probably non-functional proteins. All the affected children presented with similar phenotype at onset; the absence of phenotype-genotype correlation was discussed. A determination of the specific mutation in Anderson disease or CMRD is required to ensure diagnosis and allow prompt therapeutic intervention in these children.

Ten novel mutations in the molybdenum cofactor genes MOCS1 and MOCS2 and in vitro characterization of a MOCS2 mutation that abolishes the binding ability of molybdopterin synthase.

Molybdenum cofactor deficiency (MIM#252150) is a severe autosomal-recessive disorder with a devastating outcome. The cofactor is the product of a complex biosynthetic pathway involving four different genes (MOCS1, MOCS2, MOCS3 and GEPH). This disorder is caused almost exclusively by mutations in the MOCS1 or MOCS2 genes. Mutations affecting this biosynthetic pathway result in a lethal phenotype manifested by progressive neurological damage via the inactivation of the molybdenum cofactor-dependent enzyme, sulphite oxidase. Here we describe a total of ten novel disease-causing mutations in the MOCS1 and MOCS2 genes. Nine out of these ten mutations were classified as pathogenic in nature, since they create a stop codon, affect constitutive splice site positions, or change strictly conserved motifs. The tenth mutation abolishes the stop codon of the MOCS2B gene, thus elongating the corresponding protein. The mutation was expressed in vitro and was found to abolish the binding affinities of the large subunit of molybdopterin synthase (MOCS2B) for both precursor Z and the small subunit of molybdopterin synthase (MOCS2A).

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.