Rapid and inexpensive detection of common HBB gene mutations in Tunisian population by high-resolution melting analysis: Implication for molecular diagnosis

International audienceIn Tunisia, beta-thalassemia is a common hereditary disease with a carrying rate of 2.21%. Up to now, detection of responsible mutations was made by laborious, expensive, and/or time consuming methods. The aim of this study is to develop and validate a specific assay for detection of the two most frequent mutations in Tunisian population, the IVS-I-110 (G -> A)and Cd39 (C -> T) mutations. In this study, we optimize high resolution melting analysis (HRMA) conditions for these mutations, using control DNAs. Then, we evaluate the strength of this methodology by screening a cohort of patients with beta-thalassemia. All examined reference DNA samples were unambiguously distinguished from each other. For the blinded test, the results were completely compatible with direct sequencing, performed after the HRMA. As HRMA represents a highly sensitive and high-throughput gene scanning method, it can provide timely diagnosis at low cost for effective clinical management of beta-thalassemia

Genetic analysis of hereditary multiple exostoses in Tunisian families: a novel frame-shift mutation in the EXT1 gene

International audienceHereditary multiple exostoses (HME) is an autosomal dominant orthopaedic disorder most frequently caused by mutations in the EXT1 gene. The aim of the present study is to determine the underlying molecular defect of HME in two multigenerational Tunisian families with 21 affected members and to examine the degree of intrafamilial variability. Linkage analysis was performed using three microsatellite markers encompassing the EXT1 locus and mutation screening was carried out by direct sequencing. In family 1, evidence for linkage to EXT1 was obtained on the basis of a maximum LOD score of 4.26 at theta = 0.00 with D8S1694 marker. Sequencing of the EXT1 revealed a heterozygous G > T transversion (c.1019G > T) in exon 2, leading to a missense mutation at the codon 340 (p.Arg340Leu). In family 2 we identified a novel heterozygous 1 bp deletion in the exon 1 (c.529\₅31delA) leading to a premature codon stop and truncated EXT1 protein expression (p.Lys177LysfsX15). This mutation was associated with the evidence of an intrafamilial clinical variability and considered to be a novel disease-causing mutation in the EXT1 gene. These findings provide additional support for the involvement of EXT1 gene in the HME disease

Clinical and genetic investigation of pediatric cases of Wolff-Parkinson-White syndrome in Tunisian families.

International audienceBACKGROUND: Wolff-Parkinson-White (WPW) syndrome is an autosomal-dominant heart disease characterized by an accessory pathway that arises from an aberrant conduction from the atria to the ventricles. Several mutations within the PRKAG2 gene were shown to be responsible for WPW. This gene encodes the γ2 regulatory subunit of adenosine monophosphate (AMP)-activated protein kinase, which functions as a metabolic sensor in cells, responding to cellular energy demands. METHODS: This first study of WPW in a North African population comprises the clinical and genetic investigation of 3 Tunisian families, including 11 affected members. The involvement of the PRKAG2 and NKX2-5 genes was investigated. RESULTS: Mutation screening showed that with the exception of two already reported single-nucleotide polymorphisms, no mutations were detected within the coding region of PRKAG2 or in the NKX2-5 gene. CONCLUSIONS: This study provides further evidence of the genetic heterogeneity of WPW

rs11886868 and rs4671393 of BCL11A associated with HbF level variation and modulate clinical events among sickle cell anemia patients

International audienceAims: Fetal hemoglobin (HbF) modulates the phenotype of sickle cell anemia (SCA) by inhibiting deoxy sickle hemoglobin (HbS) polymerization. HbF genes are genetically regulated, and the level of HbF and its distribution among sickle erythrocytes is highly variable. Herein, we aimed to determine whether two functional polymorphisms of BCL11A are implicated in the variation of HbF and clinical events in SCA Tunisian patients. Material and methods: The studied population consisted of 148 SCA patients with SS phenotype. The group of patients was divided into two subgroups according to the threshold point of %HbF which is 15%. Genotyping of rs11886868 and rs4671393 was performed using PCR/Sequencing. To test for trait association with the candidate SNPs, genotype and allele frequencies between `group who had %HbF 15' (controls) were compared using Pearson's chi-square test (compare 2, version 1.02). The association of each genotype and the combined genotype with complications was performed by logistic regression test. Results: Our findings showed that the majority of patients carried genotype CT of rs11886868 and genotypes AG and GG of rs4671393 present HbF level < 15%. RR = 0.08, RR = 0.176, and RR = 0.189, respectively. The results showed a significant association between the alleles T of rs11886868 and G of rs4671393 and %HbF < 15% with P = 0.016; RR = 0.39 and P = 8.9 x 10(-3): RR = 0.567, respectively. Interestingly, the C allele of the rs11886868 and the A allele of the rs46713939 were associated with an ameliorated phenotype in patient's SCA. The combination of the genotypes GG and CT explains more phenotypic variance than the sum of the two BCL11A SNPs taken individually

Association of rs1319868, rs1567811 and rs8041224 of gene with infection among sickle cell anemia Tunisian patients

Background and aimSickle cell anemia (SCA) is characterized by variable patterns of clinical expression. Polymorphisms linked to different genes have been associated with specific complications of the disease. Herein, we focused on the study of the association of 4 polymorphisms of Insulin like Growth Factor 1 receptor (IGF1R) gene with infections, which are the major cause of death in SCA.Material and methodsThis study involved 116 sickle cell patients among whom 58 SS have the same confirmed infectious phenotype. Allele-Specific PCR was performed for the study of rs1319868, whereas the PCR/sequencing method was carried out for rs1567811, rs2872060 and rs8041224.ResultsThe results showed that rs1319868 and rs1567811 were associated with a decreased risk of infection among SS patients (p=0.038, RR=0.54; p=0.044, RR=0.56, respectively). Interestingly, the combination of different genotypes showed the association of the genotype GT of rs1319868 and the genotype CC of rs8041224 with further decreased infection risk in SCA (p=0.028, RR=0.04).ConclusionThese significant associations of IGF1R SNPs with infection suggest that this gene could play an important role in the immune function in SCA

Haplotypic classification of dystrophic epidermolysis bullosa in Tunisian consanguineous families: implication for diagnosis

International audienceDystrophic epidermolysis bullosa (DEB) is a rare genodermatosis caused by mutations in the type VII collagen gene COL7A1. Clinical diagnosis of DEB should be confirmed by histopathological and electron microscopy analysis, which is not always accessible. We report here a genetic investigation of DEB consanguineous families in Tunisia. A total of 23 EB families were genotyped with 5 microsatellite markers overlapping the COL7A1 gene. Among these families, 19 presented with the dystrophic form of EB, 9 were diagnosed by histopathological examination, 2 had the simplex form, 1 had a junctional EB, and 1 was affected by an unclassified form of EB. The informativeness of the markers was studied and allowed us to select three markers for genetic testing of DEB in Tunisian families at risk. Haplotype analysis and homozygosity by descent suggest that all families classified clinically as having DEB and the patient who presented with an unclassified form of EB are likely linked to the COL7A1 gene, and showed evidence for exclusion for the simplex and junctional cases. For COL7A1 linked families, two main haplotypes were shared by eight families. For all the other cases, haplotypic heterogeneity was observed, thus suggesting a mutational heterogeneity among Tunisian DEB families. The genetic results matched with the ultrastructural analysis in all the DEB families and with the clinical examination in 94.7% of all studied DEB families. This study is to our knowledge the first genetic investigation of DEB in the Maghrebian population. We propose a selection of informative markers and show the importance of haplotype analysis as a relatively easy and cost and time effective method for carrier screening and prenatal diagnosis of DEB in consanguineous families at risk