HLA class I and II polymorphisms in a large multiplex family with autoimmune thyroid diseases

The association of the major histocompatibility complex (MHC) antigens with Graves' disease (GD) in different ethnic groups has been previously documented. In this regard, the prevalence of HLA-B8 and DR3 antigens was found to be significantly increased in Caucasian patients (Schifferdecker et al., 1991). Recent studies of the HLA region in GD in family based studies have replicated case±control data (Heward et al., 1998; Vaidya et al., 1999). In the Tunisian population, no association between the MHC markers and GD has been reported. We investigated a large family, termed Akr, with a high prevalence of autoimmune thyroid disease (AITD). The Akr pedigree, as previously described, comprised four generations with 200 family members, including patients with either GD or Hashimoto's thyroiditis (HT) (Makni et al., 1997). At initial investigation, all patients with HT had a goitre, but this has persisted in only 23 ́8% of them and regressed in the others. A previous study of the immunoglobulin variable heavy chain (VH) and the constant region of the b chain of the T-cell receptor (TCR Cb) polymorphisms in this family showed no abnormal distribution of these polymorphisms in patients (Fakhfakh et al., 1999). In this study, we have examined the HLA class I and II gene polymorphisms in this family. The HLA class I serological typing was performed using standard complement-dependent cytotoxicity assays. For the HLA-B*37 alleles, the polymerase chain reaction-single strand polymorphism (PCR-SSP) strategy was used. HLA class II typing was done by PCR-SSP using commercial DR/DQ Generic kits (HLA DR and DQ low resolution, Dynal, France). Frequency analysis of different HLA alleles revealed a high frequency of the HLA-B*3701 and DRB1*11 alleles among patients compared to unaffected family members and the general Tunisian population (Table 1). In order to evaluate the possible implication of these alleles in AITD pathogenesis, the transmission disequilibrium test (TDT) (Spielman et al., 1993) was performed on nuclear families, having at least one heterozygous parent, and belonging to the Akr pedigree. This test has the advantage of detecting genes with modest impact in complex diseases (Risch et al., 1996) and excludes population stratification (Spielman et al., 1993). The corresponding chi-squared (1 d.f.) values were significant for B*3701 and DRB1*11 (4 ́82, P , 0 ́05 and 9 ́00, P , 0 ́05, respectively) suggesting the existence of a linkage disequilibrium in affected siblings. Comparisons of transmission between affected and unaffected offspring using a 2 2 test of heterogeneity were performed to exclude segregation distortion (Spielman et al., 1993). The corresponding chi-squared (1 d.f.) values support linkage disequilibrium with AITD for the B*3701 allele (Table 2). Thus, we found evidence for linkage between AITD and the B*3701 allele which could be itself in linkage disequilibrium with the DRB1*11 allele. This was the case for the B*3701 and B*5701 alleles which were reported to be in linkage disequilibrium with CW*0602, which is in genetic association with psoriasis disease (Rani et al., 1998). When each pathology was considered separately, the linkage disequilibrium of the B*3701 allele was observed only with GD [chi-squared (1 d.f.)  4 ́54, P , 0 ́05 for GD and chisquared (1 d.f.)  0 ́69, P . 0 ́05 for HT]. Previous studies have shown the association of the HLA-B*37 antigen with other autoimmune disorders (Coffin et al., 1989). In conclusion, we report in this study, for the first time, a linkage disequilibrium of the HLA-B*3701 allele to Grave's disease in a large multiplex Tunisian family where Grave's disease and Hashimoto's thyroiditis cosegregate.