Thyroid disorder Thyroid problems are more common in children and adults with Down syndrome than in the general population. The thyroid gland can be underactive (hypothyroidism) or overactive (hyperthyroidism). People with Down syndrome usually tend to develop hypothyroidism but sometimes they can have hyperthyroidism although this is much less common. Hypothyroidism can be present from birth but this does not happen very often. It is more likely that people with Down syndrome will develop hypothyroidism as they get older. This usually happens as a result of autoimmunity (the body’s defence system attacks itself, this is sometimes also called Hashimoto’s hypothyroidism) although there can be other causes. People with Down syndrome need regular screening blood tests throughout their lives. Babies born with Down syndrome should have a routine blood spot test in the first six weeks of life followed by a screening blood test when they reach their first birthday. Children with Down syndrome should have a screening blood test at least every two years.