T. Kammoun

A case of Kearns-Sayre syndrome with two novel deletions (9.768 and 7.253 kb) of the mtDNA associated with the common deletion in blood leukocytes, buccal mucosa and hair follicles

Kearns-Sayre syndrome is a mitochondrial disorder characterized by the emergence before the age of 20 years of progressive external ophthalmoplegia, pigmentary retinopathy, with other heterogeneous clinical manifestations. Generally, mitochondrial DNA deletions were associated with KSS but the size and position of these deletions differ among patients. This study reported a Tunisian patient with typical features of KSS. Long-range PCR amplification of the mtDNA in different tissues from this patient showed multiple mitochondrial deletions: two novel 9.768 and 7.253 kb deletions spanning respectively nucleotides 6124-15,893 and 8572-15,826 associated with the common 4.977 kb deletion.

Two new mutations in the MT-TW gene leading to the disruption of the secondary structure of the tRNATrp in patients with Leigh syndrome.

Leigh syndrome is a progressive neurodegenerative disorder occurring in infancy and childhood characterized in most cases by a psychomotor retardation, optic atrophy, ataxia, dystonia, failure to thrive, seizures and respiratory failure. In this study, we performed a systematic sequence analysis of mitochondrial genes associated with LS in Tunisian patients. We sequenced the encoded complex I units: ND2, ND3, ND4, ND5 and ND6 genes and the mitochondrial ATPase 6, tRNA(Val), tRNA(Leu(UUR)), tRNA(Trp) and tRNA(Lys) genes in 10 unrelated patients with Leigh syndrome. We revealed the presence of 34 reported polymorphisms, nine novel nucleotide variants and two new mutations (T5523G and A5559G) in the tested patients. These two mutations were localized in two conserved regions of the tRNA(Trp) and affect, respectively, the D-stem and the T-stem of the mitochondrial tRNA leading to a disruption of the secondary structure of this tRNA. SSP-PCR analysis showed that the T5523G and A5559G mutations were present with respective heteroplasmic rates of 66% and 43 %. We report here the first mutational screening of mitochondrial mutations in Tunisian patients with Leigh syndrome which described two novel mutations associated with this disorder.

Contribution of PTPN22, CD28, CTLA-4 and ZAP-70 variants to the risk of type 1 diabetes in Tunisians.

Type 1 diabetes (T1D) is caused by an immune-mediated destruction of the insulin-producing β-cells. Several studies support the involvement of T cell activation molecules. In order to underline the role of the genes involved in this pathway, we investigated, using the Sequenom MassARRAY platform, polymorphisms of sixteen single-nucleotide polymorphisms (SNPs) belonging to PTPN22, CD28, CTLA-4, and ZAP-70 genes in 76 T1D patients and 162 unrelated healthy controls from Southern Tunisia. We confirmed the association with PTPN22 (rs2476601, Corrected P (Pcorr)=0.002, OR=6.20) and CD28 gene (rs1879877, Pcorr=0.003; OR=4.27 and rs3181096, Pcorr=0.02; OR=1.73). We also identified an association with rs17695937 of ZAP-70 gene (Pcorr=0.02, OR=1.87). Our results suggest a significant effect on T1D susceptibility for A-C-A-G-C and T-C-C-T-A-C haplotypes, of ZAP-70 and CD28 genes, respectively. In addition, (A-G-C) combination of ZAP-70/CD28 gene was significantly increased in T1D patients as compared to controls, suggesting the possible interaction between these genes. These results confirm the involvement of PTPN22 and CD28 genes in the genetic susceptibility to T1D. Interestingly, ZAP-70 seems to contribute to the susceptibility to the disease in our population. However, this finding has to be confirmed in further studies.

Descriptive analyses of Turner syndrome: 49 cases in Tunisia

Turner syndrome is linked to the absence or abnormality of one of the X chromosome leading to haplo-insufficiency of genes involved in the development and maintenance of the ovarian stock in women. We report the results of a 21-year retrospective study, conducted in 49 patients with Turner syndrome. The purpose of this study was to establish the clinical, hormonal, cytogenetic and evolutive pattern of a Tunisian population with Turner syndrome and to search for correlations between genotype and phenotype. The average age of our patients at diagnosis was 14 years (1 day-42 years). Twenty-four percent of them were diagnosed in adulthood (greater than or equal to 20 years). Turner syndrome was diagnosed later in the case of mosaicism (P=0.001). Short stature was present in 85% of cases; it was more frequent among the youngest and monosomics. The dysmorphic syndrome was observed in 85% of cases; it was significantly more frequent in monosomics (P=0.003). Delayed puberty was present in 62.4% of cases, it was almost constant in monosomics (P=0.05). The loss of ovarian function was more severe in case of monosomia compared to other forms (P=0.04). Our results report a high frequency of autoimmune diseases (18/46 cases) including dysthyroidism (eight cases). Hepato biliary affections were more frequent in mosaicism compared to monosomy. The average final height was greater even in mosaicism estimated at 150.5 cm compared to 141 cm in monosomics and 138.8 cm in mosaics with abnormal structures.

Molecular investigation of distal renal tubular acidosis in Tunisia, evidence for founder mutations.

BACKGROUND Distal renal tubular acidosis (dRTA) is a rare genetic disease caused by mutations in different genes involved in the secretion of H+ ions in the intercalated cells of the collecting duct. Both autosomal dominant and recessive forms have been described; the latter is also associated with sensorineural hearing loss. METHODS Twenty-two Tunisian families were analyzed for mutations in the ATP6V1B1 and ATP6V0A4 genes by direct sequencing. Dating of the founder mutations was performed. RESULTS Two founder mutations in the ATP6V1B1 gene were found in 16/27 dRTA cases. The p.Ile386Hisfs*56 founder mutation was estimated to be older than 2400 years and no correlations were found with deafness. For the remaining patients, two mutations in the ATP6V0A4 gene, one of them being novel, were found in three Tunisian cases. The presence of a heterozygous missense mutation p.T30I, of the ATP6V1B1 gene, was identified in six patients, while no mutations of the second gene were detected. No deleterious mutations of either ATP6V1B1 or ATP6V0A were found for the two probands. CONCLUSION Our study gives evidence of phenotypic and genotypic heterogeneity of dRTA in the Tunisian population. Five different mutations were found, two of them were due to a founder effect, and screening of these mutations could provide a rapid and valuable tool for diagnosis of dRTA.

A novel m.3395A>G missense mutation in the mitochondrial ND1 gene associated with the new tRNA(Ile) m.4316A>G mutation in a patient with hypertrophic cardiomyopathy and profound hearing loss

Mitochondria are essential for early cardiac development and impaired regulation of mitochondrial function was implicated in congenital heart diseases. We described a newborn girl with hypertrophic cardiomyopathy and profound hearing loss. The mtDNA mutational analysis revealed the presence of known polymorphisms associated to cardiomyopathy and/or hearing loss, and 2 novel heteroplasmic mutations: m.3395A>G (Y30C) occurring in a highly conserved aminoacid of the ND1 gene and the m.4316A>G located in the residue A54 of the tRNA(Ile) gene. These 2 novel variations were absent in 150 controls. All these variants may act synergistically and exert a cumulative negative effect on heart function to generate the cardiomyopathy.

Aplasia cutis congenita du vertex (5 observations)

UNLABELLED Aplasia cutis congenita (ACC) is an uncommon congenital malformation. It is characterized by defects of the skin that occur most frequently on the scalp along the midline, but can also be localized on the trunk, face and limbs, usually with a symmetrical distribution. When it is localized in the skull, it can extend to the dura mater, with only the thin pia mater to protect the brain. PATIENTS AND METHODS We report a retrospective study during a period of 10 years and we report 5 cases of ACCV hospitalized in the pediatric service in CHU Hédi Chaker and in maxillo-facial surgery service in CHU Habib Bourguiba, Sfax. We studied the epidemiologic, clinical, and therapeutic aspects in our patients. RESULTS The average age at the admission was 5 days (2-8 days). A consanguinity was found in 2 cases. The clinical examination revealed cutaneous and osseous structures aplasia located in frontoparietal zone in 3 patients and in parieto-occipital zone in a patient. A hypoplasia of the toes was noted in 3 cases and a hypoplasia of the 3rd finger of the 2 hands in a case. Plain X-ray skull (3 cases) showed the osseous defect in all the cases. The cerebral IRM (2 cases) showed osseous and cutaneous defect in two cases and a lipome of the corpus callosum in one patient. A surgical repair using a cutaneous graft was performed for 3 patients. A patient died on the 16th day of life from a haemorrhage of the longitudinal sinus. The evolution was favourable in 4 cases with a cicatrisation of good quality but with subsequent alopecia. CONCLUSION ACC of the scalp is a rare and often sporadic affection. Our experience confirms that fatal bleeding from the longitudinal sinus can occur during the 1st weeks of life.

Clinical and Genetic Characterization of 26 Tunisian Patients with Allgrove Syndrome

BACKGROUND AND AIMS Allgrove syndrome is characterized by achalasia, alacrima, and adrenal insufficiency as well as being associated with progressive neurological signs. This is an autosomal recessive disorder due to mutations in the AAAS gene located on chromosome 12q13. The AAAS gene encodes a protein of 546 amino acids, ALADIN. Mutations in this genwere reported in families from North Africa and Europe. Our objective is to conduct a clinical, molecular and genetic study of 26 Tunisian patients with Allgrove syndrome. METHODS We report 26 Tunisian patients with between two and four clinical features associated with Allgrove syndrome. Blood samples were collected and isolated DNA derived from subjects was amplified. The entire sequence of the AAAS gene was analyzed by PCR and sequencing. PCR-RFLP method was performed to identify the frequent mutations found. RESULTS Sequencing of the AAAS gene revealed a major homozygous mutation (c.1331+1G>A) in 25 patients and R286X mutation in one patient. The presence of a major mutation in several unrelated affected individuals suggests the presence of a founder effect in Tunisia and allows for a fast and targeted molecular diagnosis. CONCLUSIONS We created an easy and rapid molecular enzymatic protocol based on PCR-RFLP using MvaI restriction enzyme that directly targets this major mutation and can be used for prenatal diagnosis and genetic counseling for Tunisian families at risk. To the best of our knowledge, this is the first major series report of Allgrove syndrome in Tunisia.

A Tunisian patient with Pearson syndrome harboring the 4.977kb common deletion associated to two novel large-scale mitochondrial deletions.

Pearson syndrome (PS) is a multisystem disease including refractory anemia, vacuolization of marrow precursors and pancreatic fibrosis. The disease starts during infancy and affects various tissues and organs, and most affected children die before the age of 3years. Pearson syndrome is caused by de novo large-scale deletions or, more rarely, duplications in the mitochondrial genome. In the present report, we described a Pearson syndrome patient harboring multiple mitochondrial deletions which is, in our knowledge, the first case described and studied in Tunisia. In fact, we reported the common 4.977kb deletion and two novel heteroplasmic deletions (5.030 and 5.234kb) of the mtDNA. These deletions affect several protein-coding and tRNAs genes and could strongly lead to defects in mitochondrial polypeptides synthesis, and impair oxidative phosphorylation and energy metabolism in the respiratory chain in the studied patient.

Association of TCR/CD3, PTPN22, CD28 and ZAP70 gene polymorphisms with type 1 diabetes risk in Tunisian population: family based association study.

Type 1 diabetes (T1D) is caused by an immune-mediated destruction of the insulin-producing β-cells. Several studies support the involvement of T cell activation molecules in the pathogenesis of T1D. In order to underline the role of the genes involved in this activation pathway, we investigated, using the Sequenom MassARRAY platform, 45 single-nucleotide polymorphisms (SNPs) belonging to TCR/CD3, CD28, ZAP70, and PTPN22 genes in 59 T1D Tunisian families. In the current study, we identified an association with rs706 (Z score=2.782; p=0.005) of TCRβ gene. We also demonstrated that rs10918706 in the intron of the CD3z gene was associated with increased risk of T1D (Z score 2.137; p=0.032). In the same region, rs2949655 (Z score=2.101; p=0.035) and rs1214611 (Z score=4.036; p=0.00005) showed a genotype association with the risk of T1D. When haplotypes were constructed, GAA haplotype displayed significant association with T1D (Z score=2.135; p=0.032), while GGA haplotype (Z score=-1.988; p=0.046) was negatively associated with the disease. We also identified an association with rs3181096 (Z score=2.177; p=0.029), rs17695937 (Z score =2.111; p=0.034) and rs2488457 (Z score=2.219; p=0.026), respectively of CD28, ZAP70 and PTPN22 genes. In addition, our results suggest a significant effect on T1D susceptibility for AC (Z score=2.30; p=0.02) and CTGGC (Z score=2.309, p=0.02) haplotypes of ZAP70 and PTPN22 genes, respectively. While, the GTCT (Z score=-2.114, p=0.034) and CTAGG (Z score=-2.121, p=0.033) haplotypes of CD28 and PTPN22 genes, may confer protection against T1D. These findings confirm the role of PTPN22 and CD28 involved in the T cell activation pathway in the development of T1D in Tunisian families. Interestingly, ZAP70 and TCRβ/CD3z seem to contribute to the susceptibility to the disease in our population. However, this finding has to be confirmed in further studies.