Studies have demonstrated that blood relatives of patients with Graves’ disease may carry a higher risk of developing any form of autoimmune thyroiditis. The term "autoimmune thyroiditis" is used to describe any disorder associated with the production of autoantibodies directed against structures that are part of the thyroid gland. These autoantibodies may include thyroid stimulating immunoglobulins directed against TSH receptors. They may also include other autoantibodies directed against different structures that are called anti-microsomal antibodies and anti-thyroglobulin antibodies. These autoantibodies may be associated with a disorder called Hashimoto’s thyroiditis that is marked by inflammation of tissue in the thyroid gland. In some cases, Hashimoto’s thyroiditis may progress to the point where destruction of tissue in the thyroid gland contributes to a deficiency of thyroid hormone called hypothyroidism.
Attempts have been made to clarify whether the higher incidence of autoimmune thyroiditis in certain families is entirely due to genetic factors, or whether it may represent the effect of common exposure to elements in the environment. Studies of identical twins have demonstrated that when one twin develops Graves’ disease, the other twin carries a risk of developing Graves' disease that is much higher than would be expected from simple exposure to elements in the environment. This appears to indicate that there are some genetic factors that may contribute to the development of Graves’ diseases. Specific genes that may be involved are the subject of ongoing investigation.
As a practical matter, it may be difficult to predict whether asymptomatic patients who are blood relatives of patients with confirmed Graves’ disease are likely to develop autoimmune thyroiditis. At present, there are no tables or formulas that allow for any specific calculations of risk. It may be prudent to say that these patients should be approached with a higher index of suspicion when considering whether nonspecific symptoms may be due to underlying hyperthyroidism or hypothyroidism.