Turning on the thyroid: Researchers determine mechanism that triggers normal and abnormal hormone production

Thyroid disease affects about 12 percent of the U.S. population. While many people with thyroid disease don't even know they have it, an overactive or underactive thyroid can cause a slew of problems, including weight gain or loss, mood changes and infertility. In children, an underactive thyroid can be fatal, which is why they are tested for a deficiency at birth.