Hypothyroidism (or underactive thyroid) is a common condition in which the thyroid gland makes too little thyroid hormone. About 1 in 5,000 babies is born with congenital hypothyroidism, in which the thyroid fails to grow normally and cannot produce enough hormone. There is no known cause for most cases of congenital hypothyroidism. But about 10 to 20 percent of the time, the condition is caused by an inherited defect that alters the production of thyroid hormone.
The most common inherited form of hypothyroidism is a defect of the TPO (thyroid peroxidase) gene on chromosome 2. This gene plays an important role in thyroid hormone production.
How do people get hypothyroidism?
Hypothyroidism may be caused by (1) an autoimmune disease that attacks the thyroid gland, (2) surgery or radiation to treat thyroid cancer and other conditions, or (3) rare and random genetic events in which a mutation is acquired during early embryonic development.