Clinical Studies on 3 Pairs of Monozygotic Twin Sisters Affected by Graves' Disease

Abstract

Clinical studies were undertaken of three pairs of monozygotic twin sisters affected by Graves' disease. The evidence that the twins were monozygotic was established by similarity in physical appearance, identical blood-group antigens and identical HLA types. All pairs were female, and the evidence of Graves' disease in both members of the pair was observed in 2 out of 3 pairs. In the remaining pair the disease started in the elder sister, but the younger sister still remained in euthyroidism in spite of the presence of diffuse goiter. The disease occurred in the second decade in all the patients, and the interval between the occurrence of the disease in twin sisters was 1 to 4 years. No common specific type of HLA was found among all three pairs, but DR4 was common in two pairs of twin sisters showing positive MCHA test. Serum TRAb was positive in 2 pairs of twin sisters but negative in the remaining one. However, it became positive in the elder sister of the latter pair during the antithyroid treatment. The effect of antithyroid drug treatment was found to be similar in each of the twin sisters, and the serum TRAb moved almost in parallel with serum FT4 level. These results indicate that a genetic factor may be of great importance in the aetiology of Graves' disease, and there was a strong preponderance for it to occur in women and the second decade was the peak age for its occurrence. The common specific type of HLA for all Graves' patients was not found in this study. A strong relationship was observed between Grave's disease and TRAb.