Autosomal recessive congenital cataract, intellectual disability phenotype linked to STX3 in a consanguineous Tunisian family.

The aim of this study is to investigate the genetic basis of autosomal recessive congenital cataract and intellectual disability phenotype in a consanguineous Tunisian family. The whole genome scan of the studied family was performed with single nucleotide polymorphisms (SNPs). The resulted runs of homozygosity (ROH) were analyzed through the integrated Systems Tool for Eye gene discovery (iSyTE) in order to prioritize candidate genes associated with congenital cataract. Selected genes were amplified and sequenced. Bioinformatic analysis was conducted to predict the function of the mutant gene. We identified a new specific lens gene named syntaxin 3 linked to the studied phenotype. The direct sequencing of this gene revealed a novel missense mutation c.122A>G which results in p.E41G. Bioinformatic analysis suggested a deleterious effect of this mutation on protein structure and function. Here, we report for the first time a missense mutation of a novel lens specific gene STX3 in a phenotype associating autosomal recessive congenital cataract and intellectual disability.

Clinical and genetic characterization of Bardet-Biedl syndrome in Tunisia: defining a strategy for molecular diagnosis.

Bardet-Biedl syndrome (BBS, OMIM 209900) is a rare genetic disorder characterized by obesity, retinitis pigmentosa, post axial polydactyly, cognitive impairment, renal anomalies and hypogonadism. The aim of this study is to provide a comprehensive clinical and molecular analysis of a cohort of 11 Tunisian BBS consanguineous families in order to give insight into clinical and genetic spectrum and the genotype-phenotype correlations. Molecular analysis using combined sequence capture and high-throughput sequencing of 30 ciliopathies genes revealed 11 mutations in 11 studied families. Five mutations were novel and six were previously described. Novel mutations included c.1110G>A and c.39delA (p.G13fs*41) in BBS1, c.115+5G>A in BBS2, c.1272+1G>A in BBS6, c.1181_1182insGCATTTATACC in BBS10 (p.S396Lfs*6). Described mutations included c.436C>T (p.R146*) and c.1473+4A>G in BBS1, c.565C> (p.R189*) in BBS2, deletion of exons 4-6 in BBS4, c.149T>G (p.L50R) in BBS5, and c.459+1G>A in BBS8; most frequent mutations were described in BBS1 (4/11, 37%) and BBS2 (2/11, 18%) genes. No phenotype-genotype correlation was evidenced. This data expands the mutations profile of BBS genes in Tunisia and suggests a divergence of the genetic spectrum comparing Tunisian and other populations.

Only two mutations detected in 15 Tunisian patients with 11ß-hydroxylase deficiency: the p.Q356X and the novel p.G379V.

Steroid 11ß-hydroxylase deficiency is the second most common cause of congenital adrenal hyperplasia, resulting in virilization, glucocorticoid deficiency and hypertension. The 11ß-hydroxylase enzyme is encoded by the CYP11B1 gene and mutations in this gene are responsible for this disease. The aim of this study was to characterize mutations in the CYP11B1 gene and to determine their frequencies in a cohort of Tunisian patients. The molecular genetic analysis was performed by direct nucleotide sequencing of the CYP11B1 gene in 15 unrelated Tunisian patients suffering from classical 11ß-hydroxylase deficiency. Only two mutations were detected in homozygous state in the CYP11B1 gene of all patients, the p.Q356X in exon 6 (26.6%) and the novel p.G379V in exon 7 with large prevalence (73.3%). This is the first report of screening for mutations of CYP11B1 gene in the Tunisian population and even in the Arab population.

A novel UBE3A truncating mutation in large Tunisian Angelman syndrome pedigree.

We identified in a large Tunisian pedigree a novel UBE3A frameshift mutation in exon 16 coding region, and we expect that the resulting UBE3A truncated protein in our patients is non-functional since the mutation implies the catalytic region of the enzyme. The family includes 14 affected patients born from four sisters. This mutation was found in all surviving affected individuals and their mothers pointing out the importance of genetic counseling possibility in Angelman syndrome (AS). All patients had severe mental retardation with epilepsy and microcephaly. Minor clinical expression variation was observed among the investigated patients. The severity of clinical expression is related to the detected molecular variation: deletion of 15 bp and insertion of 7 bp. These results are concordant with the gene expression observed in previously reported individuals with AS and truncated UBE3A protein.

[Genetic analysis of Turner syndrome: 89 cases in Tunisia]. / Analyse génétique du syndrome de Turner : étude tunisienne de 89 cas.

Turner's syndrome (TS) affects about 1/2500 female infants born alive. The syndrome results from total or partial absence of one of the two X chromosomes normally present in females. We report the results of a retrospective analysis of 89 cases of TS observed during a six-year period (2000-2005). The patients' age ranged from two days to 51 years at the time of this analysis. Most patients were adults (48%). The aim of this study is to ascertain the principal clinical features leading to a request for a karyotype, searching for a possible relationship between chromosomal anomalies and clinical expression of TS. Pediatric patients were referred for statural retardation or dysmorphic features, while reproduction anomalies were the main indication for karyotyping in patients aged over 20 years. Mosaicism was prevalent (47%), whereas the homogeneous karyotype 45,X was found in only 32% of the patients; structural anomalies were found in 21%. Regarding the advanced age of our patients, we established a relationship between chromosome anomalies and the clinical expression of TS, based on an analysis of stature and reproduction disorders. Short stature and primary amenorrhea were correlated with total deletion of one chromosome X or imbalanced gene dosage due to structural X anomalies. Whereas cases of infertility, recurrent miscarriages and secondary amenorrhea were associated with a mosaic karyotype pattern (45,X/46,XX or 45,X/46,XX/47,XXX ...), with a slight mosaicism in most cases. Thus, chromosome investigations should be performed in cases of reproduction failure even for women with normal stature.

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).

Neonatal death in Marshall-Smith syndrome.

Marshall-Smith syndrome is characterized by accelerated skeletal maturation, failure to thrive and dysmorphic features. Since 1971, twenty cases of MSS have been reported. We describe another patient with a very early death demonstrating the clinical variability of the syndrome and the importance of systematic X rays of the skeleton for determining the causes of fetal or neonatal death.

Y chromosome microdeletions in Tunisian infertile males.

AIM: To determine frequency of Y microdeletions in azoospermic and oligospermic Tunisian infertile males. METHODS: A Sample of 146 Tunisian infertile males with a low sperm count (<5 x 10(6) sperms per mililiter) and normal karyotype was screened for Y chromosome microdeletions. 76 men were azoospermic and 70 men were oligospermic. Genomic DNA was isolated from blood and multiplex PCR was carried out with a set of 20 AZFa, AZFb and AZFc STS markers to detect the microdeletions as recommended by the European Academy of Andrology. RESULTS: In 10/146 (6.85%) subjects AZF deletions were observed. Of these ten males with microdeletions, 9/10 subjects were azoospermic (90%), 1/10 was oligospermic (10%). Frequency of microdeletions in azoospermic men was 9/76 (11.84%). None of the patients showed isolated microdeletion in the AZFa region, but one azoospermic man had deletion in the AZFb region. Eight azoospermic patients and one oligospremic man have AZFc microdeletions. AZFc and AZFb were deleted in three azoospermic patients. AZFc, AZFb and AZFa were deleted in three azoospermic patients We estimate the sensitivity of the test comprising six STS in our sample to be 90%. CONCLUSION: The incidence of Yq microdeletions in the study population of infertile Tunisian men falls within the range published in other countries. We suggest to analyze 9STS in the first step to detect efficiently Y microdeletions in our population.

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.