Thyrotrophin receptor antibodies in type 1 (insulin-dependent) diabetes mellitus

Graves' disease and type 1 (insulin-dependent) diabetes are common autoimmune endocrine disorders which may co-exist. Since the class II HLA-DR3 antigen is associated with both these diseases, and since an association between DR3 and the thyrotrophin receptor antibody (TRAb) has been suggested, we wished to determine whether TRAb levels were increased and were HLA-D related in diabetes mellitus. In 115 clinically euthyroid subjects (33 type 1 diabetics, 82 healthy controls) there was a correlation between age and TRAb levels (r = -0.39, p less than 0.001). TRAb levels were elevated in DR3 subjects (n = 32) compared to an age matched group of non-DR3 (n = 61) subjects [median (range): 18.1 (-1.7 to 47.4) versus 6.7 (-9.8 to 19.1), p less than 0.001]. Diabetic DR3 and control DR3 subjects had similar TRAb levels which were elevated when compared to their respective non-DR3 control group (both p less than 0.001). All but two subjects (both diabetic) had TRAb levels in our normal range. Thus TRAb levels are elevated in the subjects who possess the HLA-DR3 antigen. Since DR3 is found so commonly in type 1 diabetes this phenomenon may partly explain the association with Graves' disease in this patient population.