hypothyroidism, congenital

The most common disease for which newborns are screened before leaving the hospital is congenital hypothyroidism - deficiency of thyroid hormone. Congenital hypothyroidism occurs in about 1 in 4,000 babies, with wide disparity in racial and ethnic groups. It may be mild or severe, occurring in families or arising sporadically. About 9 of ten cases are caused by failure of the thyroid gland to form properly (thyroid dysgenesis) or even to be present at all (aplasia). Since mother's thyroid hormone crosses the placenta from her bloodstream to that of the fetus, affected infants often appear normal at birth.

Congenital hypothyroidism is twice as common in girls as in boys. It is rarely diagnosed clinically, that is by examination of the patient; newborn screening tests identify most cases. Early and prolonged jaundice is an early warning sign of hypothyroidism. Sluggishness and lack of interest in nursing, excessive sleepiness, and choking spells during nursing can be present during the baby's first month. Enlargement of the tongue can cause noisy or difficult respirations and apnea spells. The abdomen is protruberant and there is often an umbilical hernia. Body temperature is low, with skin mottling of the extremities.

Mental retardation is the most serious consequence of congenital hypothyroidism. Early diagnosis and effective treatment with hormone replacement (thyroxine, Synthroid®) prevent all or most of the effects of congenital hypothyroidism. For this reason all states mandate screening of all newborns for the disease, and treatment is started even on suspicion of disease while awaiting laboratory confirmation.

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