Lack of linkage and association between autoimmune thyroid diseases and the CTLA-4 gene in a large Tunisian family

The autoimmune thyroid diseases (AITDs) including Graves' disease and Hashimoto's thyroiditis are inherited as complex traits. We have performed linkage and association studies to investigate the role of CTLA-4 gene in the AITDs development using the D2S311, D2S143, the intragenic CTLA-4 (AT)(n) microsatellite markers and the CTLA-4 (A/G) dimorphism in exon 1. Four extended pedigrees belonging to a large Tunisian family named Akr and including 154 individuals from which 20 were affected with Hashimoto's thyroiditis and 26 with Graves' disease, were used in this investigation. No evidence for linkage with none of the markers was found under neither dominant nor recessive models [Z=-7.14 and Z=-14.32 at theta=0.0, respectively for the CTLA-4 (AT)(n) marker]. A family-based association study on 51 nuclear families derived from the Akr pedigree was performed by the FBAT approach applied to the CTLA-4 (AT)(n) marker and the CTLA-4 (A/G) dimorphism. We found no association of individual alleles to disease for both markers. These results showed no evidence for the involvement of the CTLA-4 locus in the AITDs pathogenesis.