What is congenital hypothyroidism?

Causes and Symptoms

In humans, the thyroid gland
consists of two connected lobes in the front of the neck, on either side of the thyroid cartilage or Adam’s apple. It produces the thyroid hormones, the most important of which are L-triiodothyronine (T3) and L-tetraiodothyroxine or L-thyroxine (T4). These compounds circulate in the blood serum to the body’s cells and regulate virtually all metabolism: the production and consumption of proteins, carbohydrates, fats, and vitamins and the generation of energy that makes body heat. In these activities, the T3
molecule (which can be derived in the cells from T4) has two to four times the effectiveness of T4. Because of the high iodine content of both T3 and T4, sufficient dietary iodine must be supplied to maintain normal thyroid function.

Abnormal levels of T3 and T4 have a profound effect on all bodily functions. In adults, the low production of T3 and T4, known as hypothyroidism, leads to reduced mental and physical activity, weight gain, general weakness, and other symptoms. Elevated thyroid activity, or hyperthyroidism, produces restlessness and irritability, weight loss, and symptoms generally the opposite of those seen with hypothyroidism. When either of these conditions develops in adults, surgery or drug regimens, or both, are available to control them and to produce normal metabolism in the patient. When these conditions occur in utero, however, there is almost no way to counteract their effects.

A child born with congenital hypothyroidism (CH) has developmental disabilities with little or no chance of improvement and, unless immediately treated with thyroid hormones, may also be physically disabled or dwarfed, with the bone ends not growing or maturing normally. The typical infant with CH can show a variety of symptoms: low body temperature, poor appetite, decreased activity, flabbiness, low pulse rate, delayed union of bones of the skull, feeding difficulties even to the point of choking and cyanosis (turning blue from lack of oxygen), and thickened, off-color skin.

Treatment and Therapy

For the child born with CH, no treatment is available for the brain damage that has taken place. Thyroid replacement therapy from birth, using either natural or synthetic hormones, will avert most physical effects, but the intellectual disability is irreversible.

The most effective way to avoid this problem is to ensure that a pregnant woman consumes enough
iodine to be made into the T3 and T4 molecules by her fetus. The thyroid hormones do not transfer readily from the placental blood supply to that of the fetus, but the iodide ion does. This alone is enough, when made available before the end of the second trimester of pregnancy, to allow the fetal thyroid gland to develop normally, and the unborn fetus to have proper neurological and musculoskeletal function. Iodide ions are most easily supplied in iodized salt, but they can also be given as an injection of iodized oil or by the oral administration of a number of iodine-containing medicines, such as Lugol’s iodine solution.

When hypothyroidism develops in the older child or adolescent—often appearing as a goiter
, in addition to the other symptoms described above—iodine therapy is sometimes sufficient to return thyroid function to normal levels. Oddly, such therapy can also be counterproductive. The complex mechanisms that maintain proper hormone levels in blood serum can be misled by artificially high iodine concentrations and may close down hormone production because it appears high. For this condition, only thyroid hormone administration is effective.

Perspective and Prospects

Hypothyroidism, goiter, and CH are worldwide health problems because of the body’s dependence on dietary iodine. Many places in the world have low soil levels of iodine, leading to low iodine levels in crops and thus inadequate iodine intake from food. Such areas include high mountain country, such as the Himalayas, where glacial meltwater leaches iodine from the soil with no replacement from higher geologic formations, and the Ganges River basin, where the sheer volume of water removes iodine from crop lands. Some mountainous areas of the United States—such as the hill country of West Virginia, Kentucky, and Tennessee—have been, historically, centers of endemic goiter formation. Supplying iodine to inhabitants of these areas is a medical necessity but, like so many such problems, is complicated by logistic and political considerations.

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