Answering the question as to whether thyroid problems are genetic is challenging. There is very little clear direct evidence that such problems are inherited, and in some instances, other things outside of the genes may cause problems with thyroid production. What is fairly clear is that problems do often occur in families, and not just in human families, but also sometimes in certain dog breeds.
Thyroid problems include a wide range of medical conditions, but generally include the gland making too much thyroid hormone, called hyperthyroidism, or too little, which is called hypothyroidism. More or less than normal production can be linked to a variety of factors, and two autoimmune diseases can severely affect thyroid production. People with Graves' disease may have hyperthyroidism, for example, and those with Hashimoto thyroiditis may have hypothyroidism. Not all people with abnormal levels have one these diseases, however.
What isn’t clear is whether anyone who inherits a predisposition for thyroid issues will necessarily have them. Some people with strongly family history don’t end up with problems and others with minimal family history do. Of course, there are many people who have high or low thyroid levels and who never get tested or never pass on this information to family members. There is evidence that some people test slightly high or low but don’t get treatment.
Even with conditions like Graves' disease or Hashimoto thyroiditis, inheritance isn’t always clear cut. It isn’t unusual to see a whole family with Hashimoto thyroiditis, for example, but whether each affected member will pass this condition on to her children isn’t so obvious. The answer is that children may inherit the condition and may not. Since there does seem to be some links between thyroid problems and family history, it’s a good idea for individuals to know if they have this history.
People who know that they have a family history of thyroid problems should probably get checked to see if they have low or high levels of hormones. Individuals may need to be rechecked every year or two to make sure they haven’t developed a problem. It’s also important for women to get checked after having a child because there is some link between deteriorating thyroid levels after pregnancy. Women over the age of 50 are most at risk for hypothyroidism and may develop it at a later age, even if they haven’t had problems in the past.