A 20 year history of clinical and genetic study of thyroid autoimmunity in a Tunisian multigenerational family: Evidence for gene interaction.

Autoimmune thyroid diseases (AITD), which include Hashimoto thyroiditis (HT), Graves' disease (GD) and primary idiopathic myxoedema (PIM), are recognized by their clinical and genetic heterogeneity. In this study, we have carried on a global approach gathering 20 year genetic and clinical data on a Tunisian multigenerational family (Akr). Our purpose was search for a combined genotype involved in AITD susceptibility using 33 gene polymorphisms. The Akr pedigree is composed of more than 400 members distributed on 10 generations. Clinical follow-up was performed by appreciation of the thyroid gland and measurement of both thyroid hormone and auto antibody levels. We used FBAT software to test for association between gene polymorphisms and AITDs. Clinical follow-up has showed that the number of AITD patients has increased from 25 to 78 subjects subdivided on 51 cases of GD, 22 PIM and 5 HT. Concerning genetic analysis, our study has revealed new gene association when compared with our previous analysis (considering single genes). Thus, PTPN22, TG and VDR gene polymorphisms have became associated with p-values ranging from 4.6  10(- 2) to 4  10(- 3) when considered with other genes on the same chromosome; giving evidence for gene interaction. The most significant association was found with the MHC region (p = 7.15 10(- 4)). Moreover, and among gene polymorphisms explored, our analysis has identified some of them as AITD biomarkers. Indeed, PDS gene polymorphisms were associated with either exophthalmia or goiter (p-values from 10(- 2) to 10(- 3)). In conclusion, our study gives evidence for gene interaction in AITD development confirming genetic complexity of these diseases.

The first genome-wide scan in a tunisian family with generalized epilepsy with febrile seizure plus (GEFS+).

Generalized epilepsy with febrile seizure plus (GEFS+) is an autosomal dominant disorder. In the literature, 5 responsible genes were identified and 2 novel susceptibility loci for GEFS+ at 2p24 and 8p23-p21 were reported, indicating the genetic heterogeneity of this disorder. The aim of this report is to identify the responsible loci in a large affected Tunisian family by performing a 10cM density genome-wide scan. The highest multipoint logarithm of odds (LOD) score (1.04) was found for D5S407 in the absence of recombination. Two other interesting regions were found around marker D19S210 (LOD=0.799) and D7S484 (LOD=0.61) markers. To fine map these loci, additional markers in 2 regions on 5q13.3 and 7p14.2 were analyzed and positive LOD scores for both loci were obtained. Sequencing of the Sodium channel subunit beta-1 gene (SCN1B) (19q13.1) showed the absence of any causal mutation. Our findings emphasized the genetic heterogeneity of febrile seizures.

Analysis of skewed X-chromosome inactivation in females with rheumatoid arthritis and autoimmune thyroid diseases.

INTRODUCTION: The majority of autoimmune diseases such as rheumatoid arthritis (RA) and autoimmune thyroid diseases (AITDs) are characterized by a striking female predominance superimposed on a predisposing genetic background. The role of extremely skewed X-chromosome inactivation (XCI) has been questioned in the pathogenesis of several autoimmune diseases. METHODS: We examined XCI profiles of females affected with RA (n = 106), AITDs (n = 145) and age-matched healthy women (n = 257). XCI analysis was performed by enzymatic digestion of DNA with a methylation sensitive enzyme (HpaII) followed by PCR of a polymorphic CAG repeat in the androgen receptor (AR) gene. The XCI pattern was classified as skewed when 80% or more of the cells preferentially inactivated the same X-chromosome. RESULTS: Skewed XCI was observed in 26 of the 76 informative RA patients (34.2%), 26 of the 100 informative AITDs patients (26%), and 19 of the 170 informative controls (11.2%) (P < 0.0001; P = 0.0015, respectively). More importantly, extremely skewed XCI, defined as > 90% inactivation of one allele, was present in 17 RA patients (22.4%), 14 AITDs patients (14.0%), and in only seven controls (4.1%, P < 0.0001; P = 0.0034, respectively). Stratifying RA patients according to laboratory profiles (rheumatoid factor and anti-citrullinated protein antibodies), clinical manifestations (erosive disease and nodules) and the presence of others autoimmune diseases did not reveal any statistical significance (P > 0.05). CONCLUSIONS: These results suggest a possible role for XCI mosaicism in the pathogenesis of RA and AITDs and may in part explain the female preponderance of these diseases.

The R620W polymorphism of the protein tyrosine phosphatase 22 gene in autoimmune thyroid diseases and rheumatoid arthritis in the Tunisian population.

BACKGROUND: Protein tyrosine phosphatase (PTPN22) is involved in the negative regulation of T-cell responsiveness. The association of a coding variant of the PTPN22 gene (R620W) with a number of autoimmune diseases has been described. AIM: The present study investigated whether PTPN22 gene polymorphism was also involved in the genetic predisposition to autoimmune thyroid diseases (AITDs) and rheumatoid arthritis (RA) in a Tunisian case control study. SUBJECTS AND METHODS: DNA samples from 150 patients affected with RA, 204 patients affected with AITDs and 236 healthy controls were genotyped for PTPN22 R620W polymorphism (1858C/T). Genotyping was performed by the polymerase chain reaction-restriction fragment length polymorphism method. RESULTS: No significant differences in T allele frequency (2.3% in RA patients and 1% in AITDs patients vs 2.6% in controls; p=0.85 and p=0.08, respectively) and in genotype frequencies were detected between RA patients and controls (p=0.15) and between AITDs patients (p=0.11). Stratifying patients affected with AITDs according to their phenotype (Graves' disease and Hashimoto's thyroiditis) and RA patients according to the presence of rheumatoid factor (RF) and antibodies against cyclic citrullinated peptides (ACPA) did not show any significant association with PTPN22 R620W allele (p>0.05). CONCLUSION: Our data suggest that the PTPN22 C1858T single nucleotide polymorphism has no or minor effect on RA and AITDs susceptibility in the Tunisian population.

Lack of association of VDR gene polymorphisms with thyroid autoimmune disorders: familial and case/control studies.

We study the association between three Vitamin D receptor gene polymorphisms (rs10735810, rs1544410, rs731236) and susceptibility to thyroid autoimmune diseases. Seventy-six affected subjects, belonging to a large family, as well as one hundred unrelated Tunisian patients and one hundred healthy Tunisian controls were genotyped. A family-based association test and a standard chi-square test were used to assess association in family and case-control data, respectively. Our results showed no significant association of the Vitamin D receptor gene polymorphisms with the susceptibility to thyroid autoimmune diseases in the family. Moreover, allele frequencies for the three polymorphisms in the Tunisian population were similar to those reported in the Tunisian control population and none was associated with the disease. These results suggest a lack of association between the Vitamin D receptor gene polymorphisms and susceptibility to thyroid autoimmune diseases in Tunisian population, in agreement with data from the UK, but in conflict with studies from the Far East.