Congenital Hypothyroidism Congenital Hypothyroidism
The National Library of Medicine’s Genetics Home Reference

What is congenital hypothyroidism?
Congenital hypothyroidism is a condition that affects infants from birth (congenital) and results from a partial or complete loss of thyroid function (hypothyroidism). The thyroid gland is a butterfly-shaped tissue in the lower neck. It makes iodine-containing hormones that play an important role in regulating growth, brain development, and the rate of chemical reactions in the body (metabolism).

Congenital hypothyroidism occurs when the thyroid gland fails to develop or function properly. In 80 to 85 percent of cases, the thyroid gland is absent, abnormally located, or severely reduced in size. In the remaining cases, a normal-sized or enlarged thyroid gland is present, but production of thyroid hormones is decreased or absent. If untreated, congenital hypothyroidism can lead to mental retardation and abnormal growth. In the United States and many other countries, all newborns are tested for congenital hypothyroidism. If treatment begins in the first month after birth, infants usually develop normally.

How common is congenital hypothyroidism?
In North America and Europe, congenital hypothyroidism affects 1 in 3,000 to 4,000 newborns. For reasons that remain unclear, congenital hypothyroidism affects more than twice as many females as males.

What genes are related to congenital hypothyroidism?
Mutations in the PAX8, SLC5A5, TG, TPO, TSHB, and TSHR genes cause congenital hypothyroidism.

Gene mutations cause the loss of thyroid function in one of two ways. Mutations in the PAX8 gene and some mutations in the TSHR gene prevent or disrupt the development of the thyroid gland before birth. Mutations in the SLC5A5, TG, TPO, and TSHB genes prevent or reduce the production of thyroid hormones, even though the thyroid gland is present.

Mutations in other genes that have not yet been well characterized may also cause congenital hypothyroidism.

How do people inherit congenital hypothyroidism?
Most cases of congenital hypothyroidism are sporadic and occur in people with no history of the disorder in their family. An estimated 15 to 20 percent of cases are inherited. Almost all inherited cases are autosomal recessive, which means two copies of the gene must be altered for a person to be affected by the disorder. Most often, the parents of a child with congenital hypothyroidism are not affected but are carriers of one copy of the altered gene. A few inherited cases (those with a mutation in the PAX8 gene or certain TSHR mutations) have an autosomal dominant pattern, which means one copy of the altered gene is sufficient to cause the disorder.