Occurrence of Hypopituitarism in Tunisian Turner Syndrome patients: familial versus sporadic cases.

OBJECTIVE: To explore unusual association between Turner Syndrome (TS) and Hypopituitarism in a Tunisian cohort. METHODS: We reported 6 patients with TS associated to Hypopituitarism, including three familial cases except the fourth sister who showed only a TS phenotype. Biochemical analysis, resonance magnetic imaging and cytogenetic analyses were performed. RESULTS: The average age of our patients was 17.2 years (11-31 years). They were all referred for short stature and pubertal delay, except for the fourth sister who presented spontaneous puberty with the integrity of the pituitary axis and the presence of an X ring chromosome. Karyotype analysis showed monosomy in 3 cases and a mosaic TS in the 3 remaining cases, including one patient with abnormal X chromosome structure. Somatotropic and corticotropic deficiencies were confirmed in 2 sporadic cases while the gonadotropic and thyrotropic axes were spared. In contrast; familial cases were consistently affected by the integrity of the corticotropic axis. MRI showed pituitary hypoplasia in all familial cases and pituitary stalk interruption syndrome in only one sporadic case. No correlation was found between the chromosome formula and the anterior pituitary involvement. CONCLUSION: Co-segregation of congenital Hypopituitarism with pituitary hypoplasia and X chromosome aberrations could imply a molecular anomaly of transcription factors responsible for the differentiation and development of pituitary cells such as PROP1, POUF1, Hesx1, Lhx3, Lhx4. The etiopathogenic link between X chromosome abnormalities and the occurrence of Hypopituitarism remains unclear; however, the progress of molecular biology may clarify the interrelation between transcription factors and sex chromosome segregation abnormalities.

Screening of SLC26A4 gene in autoimmune thyroid diseases.

The Pendred syndrome (PS) gene, SLC26A4, was involved in the genetic susceptibility of autoimmune thyroid disease (AITD) in Tunisian population. Recently, functional assays have shown a differential expression of SLC26A4 gene between Graves' disease (GD) and Hashimoto's thyroiditis (HT). Here, by the mean of DHPLC and HRM, we explored the 21 exons and their flanking intronic sequences of 128 patients affected with GD (n = 64) or HT (n = 64). The pathogenic effect of identified variations on splice was investigated using the web server HSF. Eighteen allelic variations were identified and ranged on missense, sens and splice variations. Nine identified variations (c.-66C>G, c.898A>C, c.1002-9A>C, c.1061T>C, c.1544 + 9G>T, c.1545-5T>G, c.1790T>C, c.1826T>G, c.2139T>G) were previously reported in hearing impairment studies. Forty-seven per cent (30/64) of GD patients and 37,5% (24/64) of HT patients present at least one variant in the explored sequences. Moreover, the analysis of the variant distribution between HT (9 (5'UTR), 12 exonic and 13 intronic) and GD (18 (5'UTR), 13 exonic and 5 intronic) patients showed a significant difference (χ² = 6.54, 2df, P = 0.03). Interestingly, missense changes (I300L, p.M283I, F354S and p.L597S) affected conserved residues of pendrin. On the other hand, the HSF analyses ascertain that some variants identified in HT disease are predicted to have a pathogenic effect on splice. In conclusion, our analysis of SLC26A4 sequence variations suggested a distinct genetics basis between HT and GD patients, which should be confirmed on a large cohort.

(AT) repeat in the 3' untranslated region of the CTLA-4 gene and susceptibility to acute allograft rejection in Tunisian renal transplantation.

Allograft rejection is an immune response relying on the proliferation and the differentiation of T cells. CTLA-4 is a co-stimulatory molecule, expressed on activated T lymphocytes, which has been shown to play a crucial role in the down-regulation of T-cell activation. Herein, we have examined the impart of a genetic marker in the CTLA-4 gene on renal transplant outcomes. A cohort of 144 renal recipients and 100 healthy subjects were genotyped by the fragments analysis method using an automated sequencer. Patients were classified into two groups: Group I included 31 HLA-identical haplotype allograft recipients and Group II, 113 showing one or more HLA haplotype mismatches. Forty patients (27.78%) developed at least one acute rejection episode (ARE): 9 in Group I and 31 in Group II. Before transplantation, 20 patients were lymphocytotoxic antibodies (LCT) positive: 4 Group I, 2 of whom developed an ARE, and sixty in Group II, including 8 with an ARE. The occurrence of an ARE was associated with the presence of LCT before transplantation among the entire cohort of patients (P = .032) and among Group II (P = .037). The allelic frequencies of (AT)n polymorphism did not reveal significant differences between patients and controls. The most prevalent alleles were the 88 bp (51% in controls and 44.44% in patients) and the 106 bp (8% and 10.76%, respectively). We noticed an increase of the 120 bp allele frequency among patients who had undergone an ARE compared with those who did not display this complication (8.75% vs 3.85%). Likewise, among LCT-negative Group I, recipients the incidence of the 120 bp allele was higher in ARE than non-ARE patients. Although the differences were not statistically significant, we propose that the 120 bp allele of the CTLA-4 gene (AT)n microsatellite a predisposes to acute rejection episodes in renal transplantation.

Two missense mutations in SLC26A4 gene: a molecular and functional study.

Mutations in the SLC26A4 gene encoding pendrin, an anion transporter, are responsible for non-syndromic hearing loss (HL) (DFNB4) and Pendred syndrome (PS). PS is a genetic disorder that causes early HL and affects the thyroid gland. Here, we report eight Tunisian families affected with profound HL. Clinical investigations revealed goiter in few patients. Genotyping using microsatellite makers showed linkage to SLC26A4, and missense mutations p.L445W and p.M147T were identified by sequencing and polymerase chain reaction-restriction fragment length polymorphism. The p.L445W mutation segregated in seven families and haplotype analysis suggested its founder effect. In order to understand the molecular pathogenic mechanisms of p.L445W and p.M147T mutations, SLC26A4 wild-type and mutant cDNA constructs were transiently expressed in COS7 cells and several human cell lines including Thyroid 8305C cells. Reverse transcription-PCR, western blot and immunofluorescence demonstrated that these two mutations abolished complex glycosylation of pendrin and prevented its targeting to the plasma membrane.

Autoimmune thyroid diseases: genetic susceptibility of thyroid-specific genes and thyroid autoantigens contributions.

Autoimmune thyroid diseases are common polygenic multifactorial disorders with the environment contributing importantly to the emergence of the disease phenotype. Some of the disease manifestations, such as severe thyroid-associated ophthalmopathy, pretibial myxedema and thyroid antigen/antibody immune complex nephritis are unusual to rare. The spectrum of autoimmune thyroid diseases includes: Graves' disease (GD), Hashimoto's thyroiditis (HT), atrophic autoimmune thyroiditis, postpartum thyroiditis, painless thyroiditis unrelated to pregnancy and thyroid-associated ophthalmopathy. This spectrum present contrasts in terms of thyroid function, disease duration and spread to other anatomic location. The genetic basis of autoimmune thyroid disease (AITD) is complex and likely to be due to genes of both large and small effects. In GD the autoimmune process results in the production of thyroid-stimulating antibodies and lead to hyperthyroidism, whereas in HT the end result is destruction of thyroid cells and hypothyroidism. Recent studies in the field of autoimmune thyroid diseases have largely focused on (i) the genes involved in immune response and/or thyroid physiology with could influence susceptibility to disease, (ii) the delineation of B-cell autoepitopes recognized by the main autoantigens, thyroglobulin, thyroperoxidase and TSH receptor, to improve our understanding of how these molecules are seen by the immune system and (iii) the regulatory network controlling the synthesis of thyroid hormones and its dysfunction in AITD. The aim of the present review is to summarize the current knowledge regarding the relation existing between some susceptibility genes, autoantigens and dysfunction of thyroid function during AITD.

Association and linkage studies of the 20q11.2 region (GRD-2 locus) with Graves' disease in the Tunisian population.

OBJECTIVE: A genome-wide screen has shown linkage to the GRD-2 locus in Graves' disease (GD). Furthermore, a positional candidate gene maps to this locus; the CD40 gene has been reported to be associated and may predispose to the disease. The aim of this study was to replicate/reject the GRD-2 and to determine if the single nucleotide polymorphism (SNP) of the CD40 (CD40 C/T-1) confers susceptibility to GD. METHODS: The present study examined a dataset of 11 families with GD using 10 microsatellite markers and a case-control study consisting of 76 sporadic GD patients and 66 healthy subjects to determine the implication of the GRD-2. Both non-parametric linkage and association tests were performed. Genotyping of the CD40 C/T-1 was carried out using a polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). RESULTS: The intrafamilial association and the case-control study showed no association between CD40 C/T-1 and GD. In addition, a high percentage of the C allele (96.9%) of CD40 SNP among control data was observed. The linkage analyses showed that the highest non-parametric LOD score was 1.67 at the D20S119 marker and the maximum attainable LOD score was 1.66. This result provides interesting evidence for linkage between GRD-2 and GD. CONCLUSION: The CD40 gene seems to be not associated with GD in the Tunisian population, whereas the GRD-2 locus could harbour other candidate gene(s) to the genetic susceptibility of GD.

Screening of Y chromosome microdeletions in Tunisian infertile men.

The aim of this study was to establish the prevalence of Y chromosomal microdeletions in infertile Tunisian men. Three groups of infertile men, 65 normospermic, 53 oligozoospermic and 45 azoospermic, were tested for Yq microdeletions detection by multiplex polymerase chain reaction (PCR) using specific Y chromosome AZF regions tagged site markers (STS). One group of 13 healthy men was used as the control group. Six STS were tested (2 in each AZF region). The general prevalence of AZF microdeletions was 16%; in azoospermia and severe oligospermia groups, it was higher (29% and 30.5%, respectively). Significant differences were found with moderate oligospermic and normospermic groups (p < 0,05). AZFc microdeletions were the most frequent, and 55% of AZFc deleted patients were oligospermic. No deletions were detected in the control group. These results add to the growing literature data, showing that microdeletions of the Y chromosome is an important cause of severe spermatogenetic defect and confirm that deletion in AZFc region is the most common and is compatible with residual spermatogenesis.

Evidence for linkage and association between autoimmune thyroid diseases and the 18q12-q21 region in a large Tunisian family.

Many studies have shown linkage between IDDM6 locus on 18q12-q21 chromosome and several autoimmune diseases, suggesting that it might harbour susceptibility genes common to autoimmunity. Using 12 families deriving from a large Tunisian multiplex family (the Akr family) from which 38 people were affected with autoimmune thyroid diseases (AITD), and 193 unrelated AITD patients, tested against 100 healthy subjects, we tried to replicate the positive results previously reported for the IDDM6. Akr members were genotyped with eight microsatellite markers harbouring the IDDM6 region. Multipoint non-parametric linkage analysis have shown a clear peak values of NPL score around D18S41 marker (Z = 3.72, P = 0.0001). Family-based association test (FBAT) and transmission disequilibrium test (TDT) have confirmed linkage results. In particular, a significant association with allele 3 of D18S41 and allele 2 of D18S57 markers was found. Case-control studies, using one intragenic microsatellite (locus CTG18.1) marker in the immunoglobulin transcription factor (ITF2) gene, a 5' flanking AC repeat of the anti-apoptotic BCL-2 gene as well as two SNPs at positions +52 and +1955 from transcription start site of BCL-2, showed no significant association between neither genes and AITD. Our study is the first replication of the 18q12-q21 chromosome region as a potential candidate to AITD genetic susceptibility. The Akr family has shown evidence for linkage between IDDM6 locus and AITD. Moreover, case-control study does not support the involvement of ITF2 and BCL2 genes in AITD pathogenesis.

CTLA-4 gene polymorphisms in Tunisian patients with Graves' disease.

Graves' disease (GD) is an organ-specific autoimmune disorder of multifactorial etiology with a polygenic mode of inheritance. A recent report has demonstrated that there is a linkage and an association between the genetic markers of the CTLA-4 gene on chromosome 2q33 and GD. In order to confirm this association in a Tunisian population, three polymorphisms of the CTLA-4 gene were analyzed: the first is at the -318 position from the ATG start codon consisting of a C/T change; the second is in position 49 of exon 1, which lies in the A/G transition; and the third is in the 3' untranslated region with variant lengths of the dinucleotide (AT)n repeat. The genomic DNA from 144 patients with GD and 205 healthy individuals was genotyped after specific polymerase chain reaction amplification. Comparative analysis using a chi(2) test showed a weak yet significant difference in allele frequencies of the A/G dimorphic marker between patients and controls (P < 0.05), and a significant increase of A/A homozygous individuals among patients (21.53 vs 12.7%, P = 0.02, odds ratio (OR) = 1.89) was found. Analyses of CTLA-4 A/G polymorphism with respect to sex showed a significant difference in A/A genotypes between female patients and controls (OR = 2.14; 95%, 1.13 < OR < 4.04, P < 0.05). The distribution of CTLA-4 (AT)n allele frequencies differed between patients and controls (chi(2) = 38.18, 20 degrees of freedom, P = 0.0084) and the highest OR was found with the CTLA-4 (AT)-224-bp allele (OR = 6.43, 1.7 < OR < 28.64; P = 0.001). In conclusion, these results show that the CTLA-4 gene, or one closely associated with it, confers susceptibility to GD in a Tunisian population.

HLA-DQB1 CAR1/CAR2, TNFa IR2/IR4 and CTLA-4 polymorphisms in Tunisian patients with rheumatoid arthritis and Sjögren's syndrome.

OBJECTIVES: To evaluate the contribution of HLA class II region and the CTLA-4 gene in genetic susceptibility to rheumatoid arthritis (RA) and Sjögren's syndrome (SS) in the Tunisian population. METHODS: The polymorphisms of a (CA)n microsatellite of HLA-DQB1 CAR1/CAR2, TNFa IR2/IR4 and an (AT)n microsatellite in the 3'-untranslated region of exon 3 of the CTLA-4 gene were analysed after specific polymerase chain reaction (PCR) amplification. Typing of CTLA-4 A/G exon 1 polymorphism was achieved by the PCR-restriction fragment length polymorphism method. RESULTS: Genomic DNA from 60 patients with RA, 58 patients with SS and 150 healthy individuals was genotyped. The distribution of HLA-DQ CAR1/CAR2 allele frequencies differed between patients and controls in both diseases (RA, P<10(-15); SS, P=7.6x10(-15); RA+SS, P<10(-15)). The analysis of TNFa IR2/IR4 and CTLA-4 A/G polymorphisms did not show any differences in allele or genotype frequencies between patients and control subjects in either disease. The distribution of CTLA-4 (AT)n allele frequencies differed between patients with RA and controls (P=10(-3)), whereas no significant difference was detected between patients with SS and controls. CONCLUSION: These data suggest the involvement of HLA-DQ CAR1/CAR2 polymorphisms in genetic susceptibility to RA and SS and the participation of the CTLA-4 gene, or a gene closely associated with it, in the development of RA.

Polymorphisms of HLA DQB1 CAR1/CAR2 and TNFalpha IR2/IR4 microsatellite markers in patients affected with Graves disease.

Graves disease is an autoimmune thyroid disorder in which HLA class I and II confer susceptibility in different ethnic groups. An allele-specific polymerase chain reaction was used to characterize the variation of the HLA-DQB1 CAR1/CAR2 and TNFalpha markers located on chromosome 6 in 85 unrelated Tunisian patients affected with Graves disease and 148 healthy control subjects. In contrast to the results regarding TNFalpha alleles showing no difference between patients and controls (P = 0.904), the analysis of the HLA-DQB1 CAR1/CAR2 polymorphism showed a significant difference in its alleles (P < 0.0001). Nevertheless, no allele exhibited a predispositional effect on GD pathogenesis.