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Congenital hypothyroidism refers to hypothyroidism -- a deficiency or lack of thyroid hormone-- at birth.

In the era of newborn screening, congenital hypothyroidism is extremely rare. Still, if present, itis especially important that it be diagnosed and properly treated . Failing to properly treat

congenital hypothyroidism can negatively affect IQ and neurological development. Congenitalhypothyroidism is actually one of the most common -- yet treatable -- causes of mentalretardation worldwide.

There are two main forms of congenital hypothyroidism -- permanent congenital hypothyroidismand transient congenital hypothyroidism.

Permanent Congenital Hypothyroidism

This sort of hypothyroidism requires lifelong treatment, and has a number of causes: The most common cause of congenital hypothyroidism is a defect or abnormal

development of the thyroid gland, known as dysgenesis. In particular, abnormally located(ectopic) thyroid tissue is the most common defect. Approximately two-thirds of congenital hypothyroidism is a result of dysgenesis.

Some infants inherit defects in the ability to synthesize and secret thyroid hormone.These account for approximately 10% of cases of congenital hypothyroidism.

Congenital hypothyroidism can be due to a defect in the thyroid hormone transportmechanism.

In some infants, central hypothyroidism -- which involves hypothalamic or pituitary problems -- is the cause of congenital hypothyroidism.

Transient Congenital Hypothyroidism

It's thought that 10% to 20% of newborns who are hypothyroid have a temporary form of thecondition known as transient congenital hypothyroidism. Transient hypothyroidism in newbornshas several causes:

An iodine deficiency in the newborn, which results from insufficient iodine intake in themother

TSH-receptor blocking antibodies (TRB-Ab) in a pregnant woman with autoimmunethyroid disease transferring across the placenta and affecting thyroid function of the fetus,causing hypothyroidism at birth. This does not happen in all women with autoimmunethyroid disease. Typically, when it does, the hypothyroidism resolves in the one to threemonths after birth as the mother's antibodies are naturally cleared from the infant.

Antithyroid drugs (PTU, methimazole) taken by a pregnant woman who is hyperthyroidcrossing the placenta, causing hypothyroidism in the newborn. Usually, thehypothyroidism resolves several days after birth, and normal thyroid function returnswithin a few weeks.

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Fetus or newborn exposure to very high doses of iodine, which can cause transienthypothyroidism. This sort of iodine exposure results from use of an iodine-basedmedication like amiodarone (used to treat irregular heart rhythms) in mother or baby, or use of iodine-containing antiseptics or contrast agents.

Signs and Symptoms of Congenital Hypothyroidism

Most newborns with congenital hypothyroidism do not have any signs or symptoms of thecondition. This is due to the presence of some maternal thyroid hormone, or some residualthyroid function of their own.

But, clinical signs and symptoms can include the following:

Increased birth weight Increased head circumference

Lethargy (lack of energy, sleeps most of the time, appears tired even when awake) Slow movement

A hoarse cry

Feeding problems

Persistent constipation, bloated or full to the touch

An enlarged tongue

Dry skin

Low body temperature

Prolonged jaundice

A goiter (enlarged thyroid)

Abnormally low muscle tone

Puffy face

Cold extremities

Thick coarse hair that goes low on the forehead

A large fontanel (soft spot)

A herniated bellybutton

Little to no growth, failure to thrive

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Congenital hypothyroidism is more common in infants who have other congenital malformations(mostly heart-related) and Down syndrome.

Detection and Diagnosis of Congenital Hypothyroidism

Congenital hypothyroidism is most often detected by screening of newborns, usuallyaccomplished by a heel prick test done within a few days of birth. The test is usually followed upwithin two to six weeks after birth.

To get the latest on the current state of screening for congenital hypothyroidism, I consulted thetrusted online medical reference resource used by many physicians, UpToDate .

According to UpToDate :

"Screening of all newborns is now routine in all 50 states of the United States, Canada, Europe,Israel, Japan, Australia and New Zealand, and is under development in Eastern Europe, South

America, Asia, and Africa. In the United States, for example, more than 4 million infants arescreened annually, leading to the detection of 1000 infants with congenital hypothyroidism.Worldwide, it is estimated 12 million infants are screened and 3,000 with hypothyroidism aredetected annually."

When the initial blood screening test identifies a potential problem, follow-up typically includesadditional blood work and may include other tests, such as thyroid imaging tests . UpToDate hasextensive details regarding the various diagnostic procedures used to confirm congenitalhypothyroidism and assess its causes.

Prognosis for Congenital Hypothyroidism

If you have a child born with congenital hypothyroidism, what is his or her prognosis? If your child's condition is detected at birth and treated quickly, the prognosis is excellent. According toresearch, children detected at birth who receive early treatment typically have normal growth anddevelopment, and most studies report no difference in IQ.

Some studies, however, have found a slight reduction in verbal, math, and IQ scores, as well asslight deficits in memory and attention in some children restored to normal thyroid levels moreslowly, due to delayed diagnosis or lower starting doses. Early and sufficient treatment for congenital hypothyroidism is, therefore, especially important.

Want to learn more? See UpToDate 's topic "Clinical Features and Detection of CongenitalHypothyroidism" for additional, in-depth, current and unbiased medical information oncongenital hypothyroidism, including expert physician recommendations.

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