Thyroid autoantibodies in HLA-genotyped type 1 diabetic families: sex-limited DR5 association with thyroid microsomal antibody.

SUMMARY Thyroid autoantibodies are common in Type I diabetics and their first degree relatives and may be part of the autoimmune diathesis present within such families. We have measured the prevalence of microsomal (M-Ab) and thyroglobulin (Tg-Ab) autoantibodies in 84 HLA-typed families having a Type 1 diabetic child, using enzyme-linked immunosorbent assay techniques. Thyroid autoantibodies were detectable in 201/407 (49%) individuals in these families. Both autoantibodies were significantly more frequent in the subsets of parents, diabetic children and their non-diabetic siblings than in groups of control adults and children. The prevalence of these autoantibodies in the diabetic families was increased in both sexes with a female:male ratio of 1.4:1. Antigen DR5 was significantly associated with M-Ab production but only for male subjects (P= 0.005 after correction for the number of DR antigens tested). No significant associations were encountered for Tg-Ab. Within-family analyses indicated that thyroid autoantibodies occurred with increased prevalence in HLA-identical or haplo-identical siblings of autoantibody-positive index cases in comparison to control children. We conclude (1) the DR association with thyroid autoantibody production in this diabetes-selected population was thyroiditis-related and not diabetes-related, and (2) the DR5 association was restricted to males and the production of M-Ab. These data are consistent with the hypothesis that multiple genetic and non-genetic factors played a role in the high prevalence of thyroid autoantibodies in this population.