Sondess Hadj Fredj

Cystic Fibrosis Transmembrane Conductance Regulator Mutation Spectrum in Patients with Cystic Fibrosis in Tunisia

AIM To determine the frequency and types of mutations causing cystic fibrosis (CF) in Tunisia. METHODS We analyzed the complete coding region and flanking intronic sequences of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in 68 unrelated patients suffering from the classical form of the disease. RESULTS Twelve different CFTR mutations accounted for 90% (123/136) of CF alleles, including F508del (47.06%), E1104X (16.18%), N1303K (6.62%), 711 + 1T > G (5.88%), W1282X (4.41%), G542X (3.67%), R1158X (1.47%), 4016insT (0.74%), and R785X (0.74%). Three novel mutations were detected in this study: I1203V (1.47%), 1811 + 5A > G (0.74%), and 4268 + 2T > G (1.47%). Fifty patients (74%) were homozygous, among which 28 (41.17%) for F508del and 10 (14.7%) for E1104X. CONCLUSIONS Ninety-seven percent of patients were found with at least one CFTR mutation. This study contributes to a better knowledge on CF-causing mutations in different regions in Tunisia and demonstrates that a complete scanning of CFTR sequences is necessary to implement efficient programs for CF genetic screening and counseling in this part of North Africa.

Red cell indices: differentiation between β-thalassemia trait and iron deficiency anemia and application to sickle cell disease and sickle cell thalassemia.

BACKGROUND In Tunisia, thalassemia and sickle cell disease (SS) represent the most prevalent monogenic hemoglobin disorders with 2.21% and 1.89% of carriers, respectively. This study aims to evaluate the diagnosis reliability of 12 red blood cell (RBC) indices in differentiation of β-thalassemia trait (β-TT) from iron deficiency anemia (IDA) and between homozygous SS and sickle cell thalassemia (ST). METHODS The study covered 384 patients divided into three groups. The first one is composed of 145 control group, the second consists of 57 β-TT and 52 IDA subjects and the last one with 88 SS and 42 ST patients. We calculated sensitivity, specificity, positive-predictive values, negative-predictive values, percentage of correctly identified patients and Youdens Index (YI) for each indice. We also established new cut-off values by receiver operating characteristic curves for each indice. An evaluation study was performed on another population composed of 106 β-TT, 125 IDA, 31 SS, and 17 ST patients. RESULTS Srivastava Index (SI) shows the highest reliability in discriminating β-TT from IDA at 5.17 as a cut-off and also SS from ST with 7.7 as another threshold. Mentzer Index (MI) and RBC appear also useful in both groups with new cut-offs slightly different from those described in literature for β-TT and IDA. CONCLUSIONS The effectiveness and the simplicity of calculation of these indices make them acceptable and easy to use. They can be relied on for differential diagnosis and even for diagnosis of β-TT with atypical HbA₂ levels.

First report of cystic fibrosis mutations in Libyan cystic fibrosis patients

Background: There are few data on the molecular basis of Cystic Fibrosis (CF) in North Africa, probably due to under-diagnosis. Aim: This is the first study of cystic fibrosis transmembrane conductance regulator (CFTR) mutations in the Libyan population. Subjects and methods: This study analysed the complete coding region and flanking intronic sequences of the CFTR gene in 10 unrelated Libyan CF patients. Results: This study identified four mutations (F508del, c.1670delC, N1303K and E1104X), with a high frequency of the latter. Conclusion: Identification of CF mutations facilitates molecular investigation of cystic fibrosis in the Libyan population and helps to provide effective genetic counselling among CF families.

No association between an intronic polymorphism in the presenilin-1 gene and Alzheimer disease in a Tunisian population

We examined the potential involvement of the polymorphism in intron 8 of the presenilin-1 (PSEN1) gene as a risk factor for Alzheimer disease (AD), both through independent effect and interaction with the apolipoprotein E (APOE) ε4 allele risk, in 85 patients and 90 controls. We found no significant differences in the distribution of PSEN1 genotype and allele frequency between both groups; and post stratification distribution with APOE ε4 allele. Age of onset suggests that this polymorphism influences AD progression.

New frameshift CF mutation 3729delAinsTCT in a Tunisian cystic fibrosis patient

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Identification of a cystic fibrosis mutation W19X in Tunisia

Cystic fibrosis (CF) is a common and serious condition with autosomal recessive inheritance. It is caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). The frequencies of mutations vary according to the ethnic origin of populations. We describe in this study a patient with cystic fibrosis. She was homozygous for a new nonsense mutation identified for the first time in Tunisia: W19X, which expected to cause significant morbidity. This mutation appears to be specific to Tunisian population, although, it has identified only in CF Tunisian patients. The information provided by our study contributes to defining the molecular spectrum of CF in Tunisia, to improve genetic testing and prenatal diagnosis.

δ0-Thalassemia in cis of βKnossos globin gene: first homozygous description in thalassemia intermedia Libyans and first combination with codon 39 (C→T) in thalassemia intermedia Tunisian patients.

Abstract Background: β-Thalassemia is the most common disease among hemoglobinopathies in North African and Arab populations. In the present study we report the first description of the β-Knossos codon27 (G→T) (βKnossos) allele in cis with the δ059 (-A) mutation in thalassemia intermedia patients in Tunisia and Libya. Methods: This identification was carried out by sequencing analysis of the whole coding regions of the δ- and β-globin genes. Results: We noted that heterozygous inheritance of the βKnossos mutation results in a mild β-thalassemia phenotype with a low level of HbA2 while homozygous leads to intermediate β-thalassemia with an atypical high performance liquid chromatogram showing a complete absence of HbA2 and HbF. Compound heterozygosity of the βKnossos with β0 codon39 (C→T) is identified in a Tunisian proband for the first time and gives rise to a mild phenotype. In both families, the δ0 codon59 (-A) and the βKnossos alleles were found to be associated with a single Mediterranean β-haplotype I similar to that observed in previous reports from Algeria, Egypt, Cyprus, and Turkey. Conclusions: The chromosome supporting the βKnossos and the δ0 codon59 (-A) alleles seems to be of a single Mediterranean origin. Premarital screening studies in families in which only one of the parents has typical aspects of β-thalassemia trait and the other has a normal HbA2 level associated with abnormal red cell indices becomes a necessity to avoid missing thalassemia carriers.

Congenital afibrinogenemia: Identification and characterization of two novel homozygous fibrinogen Aα and Bβ chain mutations in two Tunisian families.

INTRODUCTION Inherited abnormalities of fibrinogen (FG) are rare coagulation disorders divided into two types: quantitative abnormalities (afibrinogenemia and hypofibrinogenemia) or qualitative abnormalities (dysfibrinogenemia and hypo-dysfibrinogenemia) of circulating fibrinogen. In particular, congenital afibrinogenemia is inherited as an autosomal recessive mode and is usually determined by homozygous or compound heterozygous mutations affecting any of the three fibrinogen genes (FGA, FGB and FGG), resulting in the complete absence or extremely reduced amount of fibrinogen. The aim of the present study was to characterize the fibrinogen abnormalities in two Tunisian families. METHODS Coagulation studies were performed on the patients and family members. All the exons and the flanking intron regions of fibrinogen genes were screened by direct sequencing. RESULTS Probands had concomitant bleeding complications with infinitely prolonged standard coagulation assays. Mutational screening of the fibrinogen gene cluster of each proband, disclosed two previously undescribed homozygous point mutations. The first mutation was a major truncation (AαArg252Stop) leads to a severe premature termination codon in the exon 5 of the FGA gene. This mutation defines in vivo the importance of the αC flexible segment in the secretion of a stable fibrinogen molecule. The second afibrinogenemic mutation (BβGly295Ala) occurs in the exon 7 of the FGB gene. This missense mutation would probably lead to significant conformational change not allowing the expression of the fibrinogen protein. CONCLUSION Current molecular characterization of these two fibrinogen abnormalities confirms the importance of the first portion of αC-region (αC-connector) as well as the Bβ globular domain in the secretion processes.

Association of M470V polymorphism of CFTR gene with variability of clinical expression of asthma: Case-report study

INTRODUCTION AND OBJECTIVES Asthma is a complex genetic disorder. Several genes have been found associated with asthma. The cystic fibrosis transmembrane conductance regulator (CFTR) gene is one of them. The aim of this study was to perform a comparative analysis of the genotype and allele frequency distributions of the biallelic marker M470V within the CFTR gene on mutant and wide chromosomes. PATIENTS AND METHODS The molecular approach consists in the genotyping of the M470V marker by the PCR-RFLP technique in 105 asthmatic patients, aged between four months and 17 years, and 105 healthy subjects. RESULTS We found a significant difference in the genotype frequencies between the two studied groups (χ2=9.855, P=0.007). The V/V genotype was over represented in the asthmatic group as compared to the controls (32.38% vs. 16.19%). Whereas, the M/V genotype is more frequent in healthy subjects (40.95% vs. 28.71%). We also noted a significant difference in allelic distribution of M470V with associated diseases (χ2=9.610, P=0.022). CONCLUSIONS The present study is the first report on the distribution of the M470V polymorphism in asthmatic Tunisian patients. We noticed that the M470V variant could modulate the clinical phenotype of asthmatic patients. This preliminary study will establish the molecular basis of this disease in Tunisia.

Angiotensin-converting enzyme insertion/deletion gene polymorphism in cystic fibrosis patients

Cystic fibrosis (CF) is the most common recessive autosomal disease in Caucasian population, caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene (Bremer et al. 2008). CF affects a number of organs but its effects on the lung constitute the major cause of morbidity and early mortality. Disease variability expression in patients bearing the same combination of mutations emphasizes the role of genetic background (modifier gene) and environment (Cutting 2005). The angiotensin-converting enzyme (ACE) gene was selected as a possible modifier gene for CF because of the proinflammatory activity of the ACE protein (Marson et al. 2012). The ACE enzyme is an important vasoconstrictor and stimulant of aldosterone; it catalyzes the transformation of angiotensin I to angiotensin II peptide and is involved in the blood pressure control, and the electrolyte balance of blood (Arkwright et al. 2003). The ACE gene is located in the 17q23.3 region of intron 16, a polymorphism based on the insertion or deletion of a 287-bp ALU repeat sequence resulting in three genotypes: DD and II homozygous and ID heterozygous (Marson et al. 2012). The aim of this work was to study the role of the ACE gene I/D polymorphism in the severity of the clinical expression of cystic fibrosis in a Tunisian CF population.