The association of autoimmune thyroid disease and type 1 diabetes
Overt autoimmune hyperthyroidism and hypothyroidism were found three times more commonly in insulin-dependent than in non-insulin-dependent diabetics. Similarly, clinically unrecognised primary autoimmune thyroid failure, as evidenced by elevation of the serum thyrotrophs concentration, was twice as common in insulin-dependent as in non-insulin-dependent diabetics. In contrast to the general insulin-dependent diabetic population, insulin-dependent diabetics with overt and clinically unrecognised autoimmune thyroid disease were characteristically female and middle-aged at the onset of diabetes. Ages at onset of diabetes and of thyroid dysfunction were correlated, suggesting the possibility of a common and coincident pathogenesis. Insulin-dependent diabetics with coexisting autoimmune thyroid disease showed a higher prevalence of HLA-B8, cytoplasmic and complement-fixing islet cell antibodies than those without thyroid disease. Within the insulin-dependent diabetic population, retinopathy was not related to the coexistence of autoimmune thyroid disease. In diabetics with elevated serum thyrotrophin concentrations but serum total thyroxine concentrations within the normal range, hypothyroidism developed at a rate of 5% per annum in patients with thyroid microsomal antibodies. Thyroid disease was more common in siblings of diabetics with thyroid disease than in those of diabetics without thyroid disease. Insulin-dependent diabetes was more common in siblings of diabetics with a personal or family history of thyroid disease than in those of diabetics without such a history. In contrast to the younger, male, insulin-dependent patients, diabetics with coexistent autoimmune thyroid disease showed no seasonal variation in incidence. Thus, the pathogenesis of diabetes, when associated with autoimmune thyroid disease, appears to be dependent upon an inherited predisposition and not on environmental factors.