[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.

Fh-Souassi: a founder frameshift mutation in exon 10 of the LDL-receptor gene, associated with a mild phenotype in Tunisian families.

Familial hypercholesterolemia (FH) has a higher prevalence in central Tunisia together with a milder clinical expression than in western countries. The molecular basis of FH in Tunisia remains unknown. Our aim was to identify FH-causing mutations in three unrelated families (21 subjects) from the area of Souassi (central Tunisia). In probands with a presentation of homozygous FH, the promoter and 18 exons of the low density lipoprotein (LDL)-receptor gene were sequenced in both orientations. A novel complex frameshift mutation was identified in exon 10, nucleotides 1477-1479 (TCT) at Serine 472 were replaced by an insertion of seven nucleotides (AGAGACA), producing a premature termination codon 43 amino acids downstream. Binding of 125I-labelled LDL at 4 degrees C to cultured fibroblasts from two probands showed <2% normal LDL-receptor activity. AvaII digestion of PCR amplified genomic DNA identified this unique mutation in all families; homozygotes n=11, heterozygotes n=10. All mutation carriers shared the same haplotype (7 RFLPs), suggesting that they had a common ancestor. Despite high plasma LDL levels (m=16.0+/-3.0 mmol/l) and extravascular cholesterol deposits, most homozygotes were diagnosed after puberty and had a delayed onset of cardiovascular complications. Moreover, most heterozygotes were free of clinical signs and had plasma LDL cholesterol in the normal range (4.7+/-1.3 mmol/l) without taking any lipid-lowering medication. This mild clinical phenotype which contrasted with the severity of the mutation, could not be explained by specific apolipoprotein E or lipoprotein lipase alleles.

[Mother-child transmission of hepatitis B virus in the Tunisian Sahel]. / Etude de la transmission mère-enfant du virus de l'hépatite B dans le Sahel tunisien.

In order to assess the importance of mother-child transmission of the hepatitis B virus (HBV) in the Tunisian Sahel, 81 HBsAg-positive mothers have been selected at delivery in a representative sample of 1940 who delivered in maternities of this region. Each HBsAg-positive mother was matched for age and parity particularly with two HBsAg-negative mothers. Children born to these 66 HBsAg+ and 120 HBsAg- mothers were traced at 28 months and tested by ELISA for HBV serologic markers (HBsAg, anti-HBs and anti-HBc). The distribution of these markers was significantly different according to the maternal status for HBsAg. The overall prevalence rate of HBV markers was higher in children born to HBsAg+ mothers as compared to children born to HBsAg- mothers (33.3% vs 13.3%, OR = 2.5, 95% CI:1.4-4.2). For HBsAg, the figures were 27.3% and 9.2% respectively (OR = 2.9, 95% CI: 1.5-5.9). Given the prevalence rate of HBsAg in mothers (4.2%), the role of mother-child transmission in the spread of HBV infection and the intensity and precocity of horizontal transmission, systemic vaccination against HBV at birth should be recommended in the Tunisian Sahel in the context of the EPI. However this decision should take into account, in terms of cost/efficacy ratio, the other public health problems concerning this area.

Phenotypic expression of familial hypercholesterolaemia in central and southern Tunisia.

We studied 14 families with familial hypercholesterolaemia (FH) from Central and Southern Tunisia. Twenty-six living homozygotes were identified in these areas of whom 24 homozygotes and 27 of their obligate heterozygote parents are the subject of this report. Ten of the 14 families are unrelated and in 9 of them there were consanguineous marriages. The mean age of homozygotes was 16 for females (range 2.5-40) and 12.5 for males (range 2-34). All the homozygotes had extensive xanthomatosis and showed variable clinical manifestations of coronary heart disease (CHD). Plasma total and LDL cholesterol levels averaged 18 and 16.9 mmol/l, respectively. Mean high density lipoprotein (HDL) cholesterol values were 0.48 mmol/l for males and 0.70 mmol/l for females. The mean age of the obligate heterozygotes was 44 (range 32-62 years) for mothers and 51 (range 35-80 years) for fathers. None of them had tendon xanthomas, not even the oldest, who was aged 80. Only 5 of the 27 obligate heterozygotes had developed CHD (aged 34-58). Plasma cholesterol levels varied more than twofold (4.1-10 mmol/l) and averaged 6.79 and 7.51 mmol/l for males and females, respectively. LDL cholesterol values were below the age- and sex-related 95th percentile from the Lipid Research Clinics Prevalence Study in 46% of male and 30% of female heterozygotes. The frequency of homozygotes was 1:125,000 and the minimum estimated frequency of heterozygotes was 1:165 in Central and Southern Tunisia. Only Afrikaners in South Africa and French Canadians have such high frequencies of FH.

[Infantile cystinosis. A new Tunisian case]. / Cystinose infantile. Une nouvelle observation tunisienne.

A case of cystinosis in a three and a half-year-old is reported. Suggestive manifestations included severe rickets, small stature, and complex renal tubule dysfunction meeting the criteria for secondary Fanconi syndrome. Diagnosis was established by the discovery of retinal lesions upon ophtalmologic evaluation and, above all, by the finding that intracellular leukocyte cystine levels were increased to 16 mumol of 1/2 cystine per gram protein. Cystinosis is severe because it inevitably leads to renal failure. Much hope is currently placed in the use of cysteamine to delay this and other complications. At present, early antenatal diagnosis during the first ten weeks of pregnancy is needed in high-risk families to allow elective termination of pregnancy within the legal time limit.