Thyroid autoimmunity: increased frequency in relatives of insulin-dependent diabetes patients.

Thyroid antibodies were found significantly more often in insulin-dependent diabetics than in their spouses or in non-insulin-dependent diabetics. The poor correlation between presence of thyroid autoimmunity and duration of disease and the significantly increased prevalence of thyroid antibodies in first-degree relatives of insulin-dependent probands are interpreted to suggest that thyroid autoimmunity in probands with insulin-dependent diabetes is not secondary to diabetes. Since married couples in which both members had thyroid antibodies were not found more frequently than predicted by chance alone, acquired environmental factors are not the sole determinants of familial thyroid autoimmunity in diabetes; it is likely that inherited predisposition is of major importance. Relatives of probands with thyroid antibodies have significantly higher frequency of these antibodies than do relatives of negative probands. This finding suggests that there are several kinds of insulin-dependent diabetes, one of which may be an "autoimmune" disease.