Overt autoimmune hyperthyroidism and hypothyroidism were found
three times more commonly in insulin-dependent than in non-insulindependent
diabetics. Similarly, clinically unrecognised primary autoim¬
mune thyroid failure, as evidenced by elevation of the serum thyrotro¬
phs concentration, was twice as common in insulin-dependent as in noninsulin-
dependent diabetics. In contrast to the general insulindependent
diabetic population, insulin- dependent diabetics with overt
and clinically unrecognised autoimmune thyroid disease were character¬
istically 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. Insulindependent
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, hypothy¬
roidism 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 diabet¬
ics without such a history. In contrast to the younger, male, insulindependent
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
