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Background: Deletions in the β-globin cluster are uncommon and cause thalassemia (thal) with hereditary persistence of fetal hemoglobin. They constitute a heterogenous group of disorders characterized by absent or reduced synthesis of adult hemoglobin (Hb A) and increased synthesis of fetal hemoglobin (Hb F). Although the clinical severity of these disorders are asymptomatic owing to the increased Hb F levels, the molecular basis is very heterogenous due to the large deletions in the β-globin cluster spanning both HBD and HBB genes. Here, we describe a Tunisian family carrying a novel deletion mutation causing (δβ)°-thalassemia., Methods: The amounts of hemoglobin fractions were measured by capillary electrophoresis of hemoglobin. Amplification and sequencing of different regions on the β-gene cluster were performed by Sanger method., Results: Family study and genetic analysis revealed a large deletion mutation in the β-globin cluster of 14.5 kb (NG_000,007.3:g. 58,253 to g.72837del14584) at the homozygous state in the patient and at heterozygous state at the other members of the family. This deletion removes the HBD and HBB genes., Conclusions: In our knowledge, this new large deletion is described for the first time in the Tunisian population and in the world, designed Tunisian(δβ) 0 in Ithanet database (IthaID: 3971). Therefore, it is important to identify the deletion leading to δβ-thalassemia carriers at the molecular level, to highlight the importance of recognizing the clinical features and implementing appropriate testing to clarify the diagnosis and manage the condition.

Objectives: Different thalassemia mutations have been reported in various ethnic groups and geographical regions in Tunisia. In the present study, we have investigated two rare β(+) -thalassemia mutations, that have not previously been reported in the Tunisian population [β -56 (G > C); HBBc. -106 G > C] and [β -83 (G > A); HBBc. -133 G > A]., Methods: The whole β-globin gene was directly sequenced, and haplotype analysis was conducted through a PCR/RFLP method., Results: Two new mutations were identified for the first time in Tunisia. They are located within the promoter region of β-globin gene at position -56 (G > C) and -83 (G > A). Linkage analysis using β-globin gene cluster haplotypes showed that these two mutations were associated with Mediterranean β-haplotype IX [- + - + + + +] and framework 2 (FW2) [CCTCT]., Conclusions: The two newly described mutations lead to the β(+) -thalassemia among Tunisian patients. The haplotype analysis and framework assignment have helped to identify the chromosomal background associated with these mutations, and determine their origin and spread., (© 2015 Wiley Periodicals, Inc.)

β-Globin haplotypes are important to establish the ethnic origin and predict the clinical development of sickle cell disease patients (SCD). To determine the chromosomal background of β (S) Tunisian sickle cell patients, in this first study in Tunisia, we have explored four polymorphic regions of β-globin cluster on chromosome 11. It is the 5' region of β-LCR-HS2 site, the intervening sequence II (IVSII) region of two fetal ((G)γ and (A)γ) genes and the 5' region of β-globin gene. The results reveal a high molecular diversity of a microsatellite configuration describing the sequences haplotypes. The linkage disequilibrium analysis showed various haplotype combinations giving 22 "extended haplotypes". These results confirm the utility of the β-globin haplotypes for population studies and contribute to knowledge of the Tunisian gene pool, as well as establishing the role of genetic markers in physiopathology of SCD.

The diversity of sickle cell disease severity is attributed to several cis acting factors, among them the single nucleotide polymorphisms (SNPs) and (AT) rich region in the β-locus control region (β-LCR). This contains five DNase I hypersensitive sites (HS) located 6 to 22 kb upstream to the ϵ gene. The most important of these is the HS2 (5' β-LCR-HS2), characterized by the presence of three different SNPs and a microsatellite region known to be in association with β(S) chromosomes in various populations. The aim of this study was to present the molecular investigation of the 5' β-LCR-HS2 site in normal and sickle cell disease individuals in order to determine if there is any correlation or specificity between these molecular markers, the β(S) Tunisian chromosomes and phenotypical expression of sickle cell disease. One hundred and twenty-four chromosomes from Tunisian individuals (49 β(S) carriers and 13 normal individuals) were screened by polymerase chain reaction (PCR) and sequencing for the polymorphic short tandem microsatellite repeats (AT)(X)N(12)(AT)(Y) and the three SNPs (rs7119428, rs9736333 and rs60240093) of the 5' β-LCR-HS2. Twelve configurations of the microsatellite motif were found with an ancestral configuration elaborated by ClustalW software. Normal and mutated alleles were observed at the homozygous and heterozygous states for the three SNPs. Correlation between microsatellites and SNPs suggests that mutant SNP alleles were mainly associated, in the homozygous sickle cell disease phenotype, with the (AT)(8)N(12)GT(AT)(7) configuration, whereas, normal SNP alleles were associated with the (AT)(X)N(12)(AT)(11) configurations in normal β(A) chromosomes. The correlation of these various configurations with Hb F expression was also investigated. The principal component analysis (PCA) showed the correlation between the homozygous sickle cell disease phenotype, mutated SNP alleles and the Benin microsatellite configuration (AT)(8)N(12)GT(AT)(7), which confirmed the specificity of this configuration to the β(S) chromosomes. In addition, the observed high level of Hb F (14.6%) could play a protective role against Hb S to justify the modulation of sickle cell disease severity within the Benin haplotype compared to the other haplotypes. This study highlights the fact that the β-LCR-HS2 could be a genetic marker to identify the ethnic Tunisian β(S) chromosomes and facilitate the molecular diagnosis of sickle cell disease.