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.