[Association between variants of lipoprotein lipase and coronary heart disease in a Tunisian population]. / Association entre des variations de la lipoprotéine lipase et la maladie coronarienne dans une population tunisienne.

OBJECTIVE: Coronary artery disease (CAD) is a complex multifactorial disease due to the interaction of multiple genes variations and environmental factors. Genetic variants of lipoprotein lipase (LPL), a key enzyme in the hydrolysis of triglyceride rich particles, may contribute to CAD. We analysed here the frequency of LPL variants (p.Asp9Asn, p.Asn291Ser and p.Ser447X) in a Tunisian population as well as their association with circulating lipid level and risk of CAD. PATIENTS AND METHODS: LPL variations were investigated by PCR-RFLP and lipid parameters were measured in 135 patients and 109 controls. RESULTS: The frequency of the p.Asp9Asn variation was 10.37% in CAD patients versus 3.66% in controls. The frequency for the p.Ser447X variation was 8.8% in CAD patients versus 13.7% in controls. There was no significant association between these two variants and CAD. The p.Asn291Ser mutation variation was absent in this population. In healthy subjects, heterozygote carriers of the p.Asp9Asn substitution had a significant increase level of total cholesterol (4.2±0.9mmol/L vs 5.6±1.2mmol/L; P=0.01) and a decreased level of HDL-cholesterol (1.36±0.3mmol/L vs 0.93±0.1mmol/L; P=0.045). CONCLUSION: There was no significant association between genetic variants of the LPL gene and CAD in this Tunisian population. The very low frequency of the p.Asn291Ser variation may be an ethnic specificity of Tunisians.

Effect of a splice site mutation in LDLR gene and two variations in PCSK9 gene in Tunisian families with familial hypercholesterolaemia.

Autosomal dominant hypercholesterolaemia (ADH) is due to defects in the LDL receptor gene (LDLR), in the apolipoprotein B-100 gene (APOB) or in the proprotein convertase subtilisin/kexin type 9 gene (PCSK9). The aim of this study was to identify and to characterize mutations at the origin of ADH in two Tunisian families. We found three genomic variations: (1) c.1845 + 1G > A, a splice site mutation in the LDLR gene and (2) two variations in the PCSK9 gene (p.Phe515Leu and p.Gly670Glu) that were both reported to be associated with high LDL-C levels. These results enlarge the spectrum of ADH-causative LDLR and PCSK9 variations in Tunisia. Our observations indicate that missense variations in the PCSK9 gene do not influence the clinical phenotype of ADH patients carrying a mutation in the LDLR gene.

+294T/C polymorphism in the PPAR-delta gene is associated with risk of coronary artery disease in normolipidemic Tunisians.

Peroxisome proliferator-activated receptor delta (PPAR-delta) is a transcription factor implicated in metabolism and inflammation. The +294T/C polymorphism in the PPAR-delta gene is associated with risk of coronary artery disease (CAD) in dyslipidemic women and hypercholesterolemic men. Whether this polymorphism influences the risk of CAD in the absence of dyslipidemia was not known, so we investigated a possible association of this polymorphism with plasma lipid and lipoprotein levels and with risk and outcome of CAD in a normolipidemic Tunisian population. Genotyping was performed by PCR-RFLP in 112 CAD patients and 113 healthy volunteers. The C-allele was significantly more frequent in patients than in controls (0.320 vs 0.189, P = 0.001). This association remained significant after adjustment for age, gender, body mass index, smoking, hypertension, and high-density lipoprotein cholesterol. Subjects carrying either one or two copies of the C-allele had a 2.7-fold higher risk of CAD than subjects homozygous for the T-allele. PPAR-delta genotypes were not associated with lipoprotein concentrations or outcome of CAD. We conclude that PPAR-delta +294T/C polymorphism is an independent risk factor of CAD in normolipidemic Tunisian subjects. The lack of association with lipoprotein concentrations suggests that the effect of the polymorphism on CAD is not mediated through lipoprotein levels in this population and that it may influence the atherosclerotic process through mechanisms involving inflammation.

Limited mutational heterogeneity in the LDLR gene in familial hypercholesterolemia in Tunisia.

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by mutations in the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes. In previous studies, we have identified novel mutations in Tunisian FH families. In this study, we have extended our investigation to additional families. Five unrelated probands were screened for mutations in the LDLR and APOB genes, using direct sequencing and enzymatic restriction. We identified two novel LDLR mutations: a missense mutation in exon 7: p.Gly343Cys (c.1027G>T), and a nonsense mutation in exon 17: p.Lys816X (c.2446A>T). Using the PolyPhen and SIFT prediction computer programs the p.Gly343Cys is predicted to have a deleterious effect on LDL receptor activity. The missense mutation we found in exon 3, p.Cys89Trp (c.267C>G), has previously been identified in patients from United Kingdom and Spain, and is reported here for the first time in the Tunisian population. Finally, the framshift mutation in exon 10, p.Ser493ArgfsX44, is reported here for the fourth and fifth time in Tunisian families. The latter is the most frequent FH-causing mutation in Tunisia. These LDLR gene mutations enrich the spectrum of mutations causing FH in the Tunisian population. The framshift mutation, p.Ser493ArgfsX44, seems to be a founder mutation in this population.

[Familial hypercholesterolemia in Tunisia]. / L'hypercholestérolémie familiale en Tunisie.

Familial hypercholesterolemia or autosomal dominant hypercholesterolemia is characterized by raised serum LDL (low density lipoproteins)-cholesterol levels, which result in excess deposition of cholesterol in tissues, leading to accelerated atherosclerosis and increased risk of premature coronary heart disease. Familial hypercholesterolemia results from defects in the hepatic uptake and degradation of LDL via the LDL receptor pathway. Familial hypercholesterolemia is commonly caused by a loss of function in the LDL receptor gene, or by a mutation in the gene encoding apolipoprotein B (APOB) or PCSK9 gene. In Tunisia, the frequency of this disease is about one of 165 for heterozygote. It is a higher frequency compared to most European countries, which is about one of 500 for heterozygote. Only five mutations in the LDLR gene were reported in this population. No mutations in the APOB or PCSK9 gene were reported.

A novel splice site mutation of the LDL receptor gene in a Tunisian hypercholesterolemic family.

BACKGROUND: Familial hypercholesterolemia (FH) is an autosomal dominant inherited disease caused by mutations in either the low-density lipoprotein receptor, the apolipoprotein B or the proprotein convertase subtilisin/kexin type 9 genes. It is characterized by a high concentration of low-density lipoprotein (LDL), which frequently gives rise to premature coronary disease. In this study, we report a novel splice site mutation of the LDL receptor gene in a Tunisian family. METHODS: Seven patients from the family were screened for mutations in the LDLR gene and the apoB gene, using direct sequencing. RT-PCR and study on cultured skin fibroblast were realised to characterize the effect of novel mutation. RESULTS: Direct sequencing of the promoter and 18 exons reveals a G>A substitution in the splice site junction of intron 8 (c.1186+1 G>A). Study on cultured skin fibroblasts showed a residual activity of 10% of the LDL receptor. Reverse transcription, amplification and direct sequencing of RNA from patient's lymphocytes reveal a deletion of the final 51 bp of exon 8 preserving the reading frame. CONCLUSIONS: The study identified a novel splice mutation c.1186+1 G>A in the LDL receptor gene. It causes the utilization of a new cryptic donor splice site 51 bp downstream from the normal site.