Ahlem Amouri

Consanguinity, endogamy, and genetic disorders in Tunisia

Consanguinity refers to marriages between individuals who share at least one common ancestor. In clinical genetics, a consanguineous marriage is defined as a union between two individuals who are related as second cousins or closer, with the inbreeding coefficient (F) equal or higher than 0.0156 (Bittles2001). However, reports on consanguinity rates may sometimes include marriages between third cousins or more distantly related individuals (Hamamy2011). It is estimate that more than 690 million people in the world are consan- guineous (Bittles and Black 2010 ). Middle East, Northern Africa, and South Asia are regions that have historically and culturally had a high rate of consanguineous unions (Al- Awadi et al. 1985; Al-Gazali et al.1997; Jaber et al.1997;Bittles et al.2002; Bener and Alali2006). Recent studieshave shown that 20 % to 50 % of marriages in Arab countries are between relatives (Tadmouri et al. 2009;Bittles2011; Hamamy et al.2011). The rate was 68 % inEgypt (Mokhtar and Abdel-Fattah2001), 51-58 % in Jordan

Fanconi anemia in Tunisia: high prevalence of group A and identification of new FANCA mutations

AbstractFanconi anemia (FA) is a rare autosomal recessive disease characterized by progressive pancytopenia, congenital malformations, and predisposition to acute myeloid leukemia. Fanconi anemia is genetically heterogeneous, with at least eight distinct complementation groups of FA (A, B, C, D1, D2, E, F, and G) having been defined by somatic cell fusion studies. Six genes (FANCA, FANCC, FANCD2, FANCE, FANCG, and FANCF) have been cloned. Mutations of the seventh Fanconi anemia gene, BRCA2, have been shown to lead to FAD1 and probably FAB groups. In order to characterize the molecular defects underlying FA in Tunisia, 39 families were genotyped with microsatellite markers linked to known FA gene. Haplotype analysis and homozygosity mapping assigned 43 patients belonging to 34 families to the FAA group, whereas one family was probably not linked to the FANCA gene or to any known FA genes. For patients belonging to the FAA group, screening for mutations revealed four novel mutations: two small homozygous deletions 1693delT and 1751–1754del, which occurred in exon 17 and exon 19, respectively, and two transitions, viz., 513G→A in exon 5 and A→G at position 166 (IVS24+166A→G) of intron 24. Two new polymorphisms were also identified in intron 24 (IVS24–5G/A and IVS24–6C/G).

Genetic homogeneity of mutational spectrum of group-A xeroderma pigmentosum in Tunisian patients

Background  Xeroderma Pigmentosum (XP) is a rare autosomal recessive disorder characterized by cutaneous and ocular alterations. Eight genes, Xeroderma Pigmentosum group A (XPA) to Xeroderma Pigmentosum group G (XPG) and Xeroderma Pigmentosum group V (XPV), are known to be responsible for the disease and products of these genes are involved in the repair of deoxyribonucleic acid (DNA) lesions generated by UV radiation. Several XP patients suffer from neurological defects, found in the XPA (the most common form), D and G groups. The aim of this study was to investigate the mutational spectrum of XPA in Tunisia, in order to propose a simple tool for molecular diagnosis.

A novel POLH gene mutation in a xeroderma pigmentosum-V Tunisian patient: phenotype-genotype correlation.

XP occurs at higher frequency in Tunisia (1:10,000) than in Japan (1:22,000) (Hirai et al. 2006) and the United States (1 per million) (Kleijer et al. 2008). XP-V cells are unable to synthesize intact daughter DNA strands on UV-irradiated templates resulting from an inability to carry out translesion synthesis (Lehmann et al. 1975; Masutani et al. 1999). Approximately 20% of XP patients belong to XP-V complementation group (Gratchev et al. 2003). In Tunisia, XP is classified into three clinical forms: severe, intermediate with or without neurological abnormalities, and moderate (Zghal et al. 2006). Previous molecular investigation showed homogeneity of mutational spectrum in XPA and XPC genes (Ben Rekaya et al. 2009; Messaoud et al. 2010a,b). The moderate clinical form of XP is characterized by mild dermatological manifestations, no neurological abnormalities and late onset of skin cancers. The median age of onset is 4 years. Mild skin symptoms and late onset of skin tumours have been already described in XP-V (Tanioka et al. 2007), XP-F (Matsumura et al. 1998) and XP-E patients (Rapic-Otrin et al. 2003). Post-UV cell survival in the presence or absence of caffeine (Itoh et al. 2000), unscheduled DNA synthesis (UDS) and detection of polymerase eta employing Western blot (Tanioka et al. 2007) cannot define exactly the molecular defects are in the polymerase eta. These laboratory assays are used to find out the UV sensitivities of the patients’ cells and the DNA repair status of their cells as

Cytogenetic abnormalities in Tunisian women with premature ovarian failure

To identify the distribution of chromosome abnormalities among Tunisian women with premature ovarian failure (POF) referred to the department of Cytogenetic at the Pasteur Institute of Tunis (Tunisia), standard cytogenetic analysis was carried out in a total of 100 women younger than 40 affected with premature ovarian failure. We identified 18 chromosomal abnormalities, including seven X-numerical anomalies in mosaic and non-mosaic state (45,X; 47,XXX), four sex reversal, three X-structural abnormalities (terminal deletion and isochromosomes), one autosomal translocation and one supernumerary marker. The overall prevalence of chromosomal abnormalities was 18% in our cohort. X chromosome aneuploidy was the most frequent aberration. This finding confirms the essential role of X chromosome in ovarian function and underlies the importance of cytogenetic investigations in the routine management of POF.

The experience of a Tunisian referral centre in prenatal diagnosis of Xeroderma pigmentosum.

Aims: Xeroderma pigmentosum (XP, OMIM 278700-278780) is one of the most severe genodermatoses and is relatively frequent in Tunisia. In the absence of any therapy and to better manage the disease, we aimed to develop a molecular tool for DNA-based prenatal diagnosis. Methods: Six consanguineous Tunisian XP families (4 XP-A and 2 XP-C) have benefited from a prenatal diagnosis. Screening for mutations was performed by direct sequencing, while maternal-foetal contamination was checked by genotyping. Results: Among the 7 prenatal diagnoses, 4 foetuses were heterozygous for the screened mutation. Exclusion of contamination by maternal cells was checked. Mutations were detected at a homozygous state in the remaining cases, and the parents decided to terminate pregnancy. Conclusion: Our study illustrates the implementation of prenatal diagnosis for better health support of XP in Tunisia.

Differential impact of consanguineous marriages on autosomal recessive diseases in Tunisia.

Consanguinity is common in Tunisia. However, little information exists on its impact on recessive disorders. In this study, we evaluate the impact of consanguineous marriages on the occurrence of some specific autosomal recessive disorders and consider how other factors, such as population substructure and mutation frequency, may be of equal importance in disease prevalence.

Chromosomal evaluation in a group of Tunisian patients with non-obstructive azoospermia and severe oligozoospermia attending a Tunisian cytogenetic department

Male infertility is the cause in half of all childless partnerships. Numerous factors contribute to male infertility, including chromosomal aberrations and gene defects. Few data exist regarding the association of these chromosomal aberrations with male infertility in Arab and North African populations. We therefore aimed to evaluate the frequency of chromosomal aberrations in a sample of 476 infertile men with non-obstructive azoospermia (n=328) or severe oligozoospermia (n=148) referred for routine cytogenetic analysis to the department of cytogenetics of the Pasteur Institute of Tunis. The overall incidence of chromosomal abnormalities was about 10.9%. Out of the 52 patients with abnormal cytogenetic findings, sex chromosome abnormalities were observed in 42 (80.7%) including Klinefelter syndrome in 37 (71%). Structural chromosome abnormalities involving autosomes (19.2%) and sex chromosomes were detected in 11 infertile men. Abnormal findings were more prevalent in the azoospermia group (14.02%) than in the severe oligozoospermia group (4.05%). The high frequency of chromosomal alterations in our series highlights the need for efficient genetic testing in infertile men, as results may help to determine the prognosis, as well as the choice of an assisted reproduction technique. Moreover, a genetic investigation could minimize the risk of transmitting genetic abnormalities to future generations.

Prevalence of Y chromosome microdeletions in infertile Tunisian men

Yq microdeletions are the leading genetic cause of male infertility and its detection in clinically relevant for appropriate genetic counseling. The objective of this study was to determine the frequency of Y microdeletion in a group of Tunisian infertile men and to compare the prevalence of these abnormalities with other countries and other Tunisian reported series. Totally, 105 Tunisian idiopathic infertile men (74 azoospermic and 31 severe oligozoospermic) were screened for the presence of Y chromosome microdeletions. The screening of Yq microdeletions was performed by two multiplex PCRs using six STS markers recommended by the EAA/EMQN. No microdeletions were detected in the men with severe oligozoospermia. In the azoospermic group, 2/74 (2.7%) patients showed Y chromosome microdeletions. Both had complete deletion of the AZFc region. No microdeletion was identified in the AZFa region or in the AZFb region. The estimated frequency of Y chromosome microdeletions in the present survey was similar to some other reports but lower than that of previous reports in Tunisian populations.

Differentiation of Fanconi anemia and aplastic anemia using mitomycin C test in Tunisia

Fanconi anemia (FA) is a recessive chromosomal instability syndrome that is clinically characterized by multiple symptoms. Chromosome breakage hypersensitivity to alkylating agents is the gold standard test for FA diagnosis. In this study, we provide a detailed laboratory protocol for accurate assessment of FA diagnosis based on mitomycin C (MMC) test. Induced chromosomal breakage study was successful in 171 out of 205 aplastic anemia (AA) patients. According to the sensitivity of MMC at 50 ng/ml, 38 patients (22.22%) were diagnosed as affected and 132 patients (77.17%) as unaffected. Somatic mosaicism was suspected in an 11-year-old patient with a FA phenotype. Twenty-six siblings of FA patients were also evaluated and five of them (19.23%) were diagnosed as FA. From this study, a standard protocol for diagnosis of FA was developed. It is routinely used as a diagnostic test of FA in Tunisia.