Down Syndrome and Hypothyroidism

Child with Down syndrome

People with Down syndrome are at an increased risk of developing hypothyroidism. Hypothyroidism is a surprisingly common disorder that can affect people of all ages and occurs in about 1 in 4,000 people. The incidence is higher in people with Down syndrome. Anywhere from 13 to 55% of people with Down syndrome will develop hypothyroidism over the course of their lifetime. It is unclear why people with Down syndrome have such an increased chance to develop hypothyroidism. The good news is that it is easily treated with medication.

To understand hypothyroidism, it is important to understand what the thyroid is and the function that it normally performs in the body.

What Is the Thyroid?

Your thyroid is a small butterfly-shaped gland located in your neck, in front of the Adam's apple. The thyroid is part of the endocrine or hormone system. While we typically associate hormones with teenagers and sex, they actually play a very important role in regulating many of the body’s activities including metabolism and energy levels.

What Is Hypothyroidism?

Hypothyroidism is a condition caused by having too little thyroid hormone (thyroxine) in the bloodstream. When someone is diagnosed with hypothyroidism, their thyroid gland is said to be “underactive” - it is not producing enough thyroid hormone. The symptoms of hypothyroidism are somewhat similar to the symptoms and features of Down syndrome, and it can be difficult to tell the difference between the two diagnoses. The symptoms of hypothyroidism include decreased growth rate, constipation, lethargy or tiredness, decreased muscle tone and dry skin and hair - all things that can occur in people diagnosed with Down syndrome.

What Is Thyroid Hormone?

Thyroid hormone, called thyroxine, exists in the body in two different forms called T3 and T4. T4 is the most common form in the bloodstream, and it is converted to T3 when it is working in the body. The amount of T4 is produced by the thyroid is dictated by a hormone called thyroid stimulating hormone (TSH). TSH stimulates the thyroid to produce T4, which is then turned into T3 in the body. When the thyroid becomes less active, it starts producing less T4 than the body needs. In an attempt to correct this problem, the body starts producing more and more TSH, to try to stimulate the underactive thyroid to produce more hormones. So to sum it up, when your thyroid is underactive, there are decreased levels of T4 and T3 in your bloodstream, and an increased level of TSH.

How Hypothyroidism Is Diagnosed in People With Down Syndrome

Because people with Down syndrome have an increased chance to develop hypothyroidism, they are “screened” or tested for this disorder regularly, by blood tests, over the course of their lives.

Most infants in this country, with and without Down syndrome, are screened for congenital hypothyroidism at birth through their state-run newborn screening program. If the newborn screen test is positive, or if your doctor sees other signs of hypothyroidism in your newborn he or she may order further blood tests to confirm this diagnosis.

As your baby gets older, he or she will continue to have testing for hypothyroidism. It is recommended that all infants with Down syndrome be tested for hypothyroidism by blood tests that measure thyroid hormone levels at six months, one year and every year after that for life.


Hypothyroidism is treated by replacing the missing the naturally occurring thyroid hormone with a synthetic replacement called levothyroxine (brand name Synthroid). Levothyroxine is a pill that is taken daily and must be taken for the rest of a person's life. Babies with hypothyroidism may be treated with a liquid version of levothyroxine until they can handle swallowing a pill. Once a person has started treatment, their doctor will continue to monitor their hormone levels and their symptoms, to make sure that they are receiving the right amount of levothyroxine.

Bottom Line

Hypothyroidism is a highly treatable disorder that occurs more frequently in people with Down syndrome. Because the symptoms of hypothyroidism are so subtle and overlap with Down syndrome, all people with Down syndrome should have yearly blood work to check if they have developed this disorder.

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