Prenatal diagnosis of chromosome disorders in Tunisian population.

Cytogenetic prenatal diagnosis (PND) is under national health program in most developed countries, while it concerns a small part of population at risk in developing countries. Finance is common reason of absence of PND development, but socio-cultural believes play an important role in Arab Muslim countries. In this paper we report results of 3110 fetal karyotypes carried out in a Tunisian population, by cultured amniocytes analysis. It is the largest report in a Muslim Arab country in our Knowledge. Abnormal karyotypes rate was 4.18% classified in two groups: bad prognosis (3.05%) and good prognosis (1.13%). Common amniocentesis indication was maternal age. The highest predictive value was observed in balanced karyotype and fetal ultrasound findings indications. Maternal serum markers were not commonly used for trisomy 21 screening. Pregnancy termination that is permitted by legal and religious authorities was accepted by 94,74% parents. Information about PND outcomes was given by genetic counselling prior to fetal sampling, pregnancy interruption was discussed with parents at cytogenetic result announcement. The authors conclude that in order to prevent mental and physical handicap related to cytogenetic disorders we have to promote PND by education for population, genetic counselling and fetal ultrasound screening; all three methods available in Tunisia.

Refined 2.7 centimorgan locus in Xp21.3-22.1 for a nonspecific X-linked mental retardation gene (MRX54).

Nonspecific X-linked mental retardation (MRX) is a heterogeneous condition in which mental retardation (MR) appears to be the only consistent manifestation. A large genetic interval of assignment obtained on individual families by linkage analysis, genetic, heterogeneity, and phenotypic variability usually are major obstacles to fine-map and identify the related disease genes. Here we report on a large Tunisian family (MRX54) with an MRX condition. X-linked recessive inheritance is strongly suggested by the segregation of MR through seven unaffected carrier females to 14 affected males in two generations. Two-point linkage analysis demonstrated significant linkage between the disorder and several markers in Xp21.3-22.1 (maximum LOD score Zmax = 3.56, recombination fraction 0 = 0 at DXS1202), which was confirmed by multipoint linkage analyses. Recombinant events observed with the flanking markers DXS989 and DXS1218 delineate a refined locus of approximately 2.7 cM in accordance with the physical distance between these two markers. The small interval of assignment observed in this family overlaps not only with nine large MRX loci previously reported in Xp21.3-22.1 but also with two inherited microdeletions in Xp21.3-22.1 involved in nonspecific MR. Although the involvement of several genes located in the Xp21.3-22.1 region cannot be ruled out, data reported in this study could be used as a starting point for the search of such gene(s).