Medically reviewed by
Dr. Minako Abe, M.D., Board-certified emergency medicine physician researching the relationship between lifestyle and disease onset in relation to the immune system and cancer, Japan
The thyroid gland is a small butterfly-shaped organ located at the base of the neck. It regulates energy metabolism, brain development and overall growth through its release of the thyroid hormone (T4 and T3). The thyroid gland typically releases thyroxine (T4), a substantially inactive form of the thyroid hormone, which some organs convert to its active form, triiodothyronine (T3). Also secreted by the thyroid gland is triiodothyronine (T3).
The two main thyroid conditions, characterized by an overproduction of thyroid hormone (hyperthyroidism) or underproduction of thyroid hormone (hypothyroidism), have different causes. Most cases of hyperthyroidism result from an autoimmune disease known as Graves’ disease. Similarly, Hashimoto’s disease, another autoimmune disease, is responsible for most cases of hypothyroidism. Euthyroidism is the name given to the condition of having an optimal level of thyroid hormone in your body.
Anyone can be affected by thyroid diseases, irrespective of sex or age. However, some people are more susceptible to developing thyroid conditions. Also, while some develop thyroid conditions at some point in their life significantly much later after birth, others are born with them. Congenital thyroid disorders, sometimes referred to as neonatal thyroid disorders, come in various forms and are present at birth, as the name implies. So, are children born with these conditions because their parents passed them on? In some cases, yes, and in other cases, no. A hyperthyroid or hypothyroid child can be born to euthyroid parents. Having hyperthyroid or hypothyroid parents give birth to a euthyroid child is also possible. Many factors, such as genetics, come into play in these instances, although congenital thyroid disorders often seem to occur sporadically without a genetic predisposition.
In cases where genetic factors are absent, other factors, such as pregnancy conditions, including quality of diet during pregnancy, could affect the thyroid development of the fetus. For instance, a lack of iodine in a pregnant woman’s diet, regardless of her thyroid condition, could result in congenital hypothyroidism in her unborn child. This is because the baby needs iodine to make the thyroid hormone. Also, if a pregnant woman develops a thyroid condition which is left untreated, it can result in the development of thyroid problems in the fetus. In extreme cases, it could be fatal.
Aside from the rare instances of thyroid disease being directly passed on from parent to offspring through genetic mutation, it is important to acknowledge that maternal thyroid disorders can also impact the overall well-being of the infant. For instance, thyroid problems during pregnancy may result in pregnancy loss, premature birth, low birthweight, or congestive heart failure in the infant.
The rest of this article highlights two main distinct forms of congenital thyroid disorders:
- Congenital hypothyroidism
- Congenital hyperthyroidism
Congenital hypothyroidism is a condition characterized by thyroid hormone deficiency present at birth. Congenital hypothyroidism can lead to intellectual disability if left untreated. Thanks to newborn screening programs, neurological deficits that result from congenital hypothyroidism can be prevented. Early detection and treatment of this disorder guarantee normal growth of the child. This condition can be managed with levothyroxine. The dosages of the prescription will require some adjustments by a pediatric endocrinologist as the child grows.
The incidence of congenital hypothyroidism is higher in females than males. The reason for this, however, is yet to be scientifically established. This disorder occurs due to a lack of iodine in a pregnant mother’s diet. The advent of iodized diets is believed to have significantly reduced the incidence of congenital hypothyroidism. Compared to congenital hyperthyroidism, congenital hypothyroidism is apparently more common, although both are collectively not very common. Congenital hypothyroidism occurs in about 1 in every 2,000 to 4,000 newborns.
This condition comes in various forms, namely:
- Thyroid dysgenesis — This is a developmental defect of the thyroid gland characterized by an absent or underdeveloped thyroid gland. While its cause remains largely unknown, this is the most common form of congenital hypothyroidism. It is twice as common in females as in males. Studies suggest that only a small percentage (about 2% to 3%) of this condition is inherited.
- Thyroid dyshormonogenesis — This occurs when the thyroid gland is present, but thyroid hormone production is minimal or absent due to genetic mutations that disrupt the production of thyroid hormones. The thyroid gland may be either normal-sized or enlarged (goiter).
- Central/pituitary hypothyroidism — This is a disorder where the pituitary gland, which is located at the base of the brain, is unable to properly stimulate the thyroid hormone production process, resulting in diminished levels of the thyroid hormone, even though the thyroid gland is, in this case, functioning normally. Typically, the pituitary gland produces enough thyroid-stimulating hormone (TSH) to induce thyroid hormone production by the thyroid gland. However, a defective pituitary gland, hypothalamus, or both disrupt this process.
Syndromic congenital hypothyroidism — This is when congenital hypothyroidism occurs as part of syndromes affecting other organs of the body. Brain-lung-thyroid syndrome and Pendred syndrome are examples of this condition.
The most common cause of congenital hyperthyroidism in newborns is Graves’ disease in the mother. Neonatal Graves’ disease (GD), also known as neonatal hyperthyroidism, remains the most common cause of hyperthyroidism in neonates and is potentially fatal if not detected and treated early by a pediatric endocrinologist. An increased level of circulating and free T4 with a concomitantly decreased level of TSH in the blood of the neonate or fetus is typically indicative of hyperthyroidism. Treatment can begin as early as the fetal stage before the baby is born. While still a fetus, the condition at this stage can be treated using antithyroid medication taken by the mother.
Neonatal GD occurs in about 1% to 5% of infants born to mothers with GD and may cause permanent impairment of brain development if it is not detected and treated early. Although this disorder is rare, it is transient (not permanent). This condition occurs when a mother with Graves’ disease passes her thyrotropin receptor antibodies (TrAb) to her child. These antibodies cross the placenta and stimulate the thyroid gland of the baby. Once these antibodies are cleared from the infant’s bloodstream, the disease should finally disappear.
In the meantime, antithyroid medication is used to manage the condition before the antibodies are cleared from the baby’s blood circulation. Essentially, the prognosis of this condition is good with early detection and treatment. It is also best to still have your child regularly checked by a pediatric endocrinologist, as it is possible for the child to develop a thyroid condition later in the first year of life.
- Can you pass your thyroid disease to your child? Yes, you can, but it is generally not very likely. Genetic factors only account for a small fraction of cases of congenital hypothyroidism.
- Can a child be born with a thyroid condition even if one or both parents are euthyroid? Yes, this is possible, albeit rare.
- Thyroid disorders can develop at any stage of life. Anyone can be affected, even though some people may be at a higher risk.
- Congenital hypothyroidism remains one of the easily preventable causes of intellectual disability. Early diagnosis and treatment prevent neonates from growing with neurodevelopmental challenges.
- Neonatal Graves’ disease, albeit rare, is eminently treatable without permanent sequelae if detected early.
- Newborn screening of congenital thyroid disorders is essential so treatment can begin soon after a diagnosis. Pediatric endocrinologists usually treat cases of congenital thyroid disorders.