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Causes of congenital hypothyroidism Agenesis:- absence of the thyroid gland altogether.  It wasn't formed during the fetal period, when the baby's organs were developing. Disorders of thyroid hormonogenesis:- some hormones play an essential part in the manufacture of the hormones in the thyroid gland.  If they are defective or absent, thyroid hormones are not formed. Endemic cretinism:- owing to a deficiency of iodine, an element essential for manufacture of the hormones.  This needs addition of iodine to the diet, for example, as iodised salt. Pituitary gland disorders:- the pituitary gland, at the base of the brain, controls the thyroid by a hormone called the thyroid stimulating hormone (TSH).  If the pituitary doesn't produce enough TSH, thyroid hormone production will be low.

Congenital Hypothyroidism (Cretinism)

The thyroid is a gland in the neck.  Normally, we don't even notice it, but a defect in its functioning at birth can have lifelong consequences.  The thyroid gland produces three hormones called thyroxine, triiodothyronine, and calcitonin.  The first two are esential for growth, brain development, and many other bodily functions.  Deficiency or absence of these hormones at birth is congenital hypothyroidism.

Problems of hypothyroidism

The thyroid hormones are needed by almost all the body organs, but are especially important for the growing brain.  If not identified quickly and treated adequately, congenital hypothyroidism can leave permanent defects.  These children may have mental retardation, deafness, poor growth (low adult height), and other nervous system disorders.

Children with untreated congenital hypothyroidism have a slow heart rate, a weak cry, constipation, mottling of the skin (a lace like appearance), swelling on the face and limbs, protrusion of the tongue, and cool hands and feet.   Jaundice of the newborn  is often prolonged in these babies.  There is often a swelling at the belly button, called an umbilical hernia.  Most of these can be reversed by treatment.  Not all children show all these signs, and the diagnosis of congenital hypothyroidism is sometimes difficult, leading to delay in starting treatment.  The brain damage is irreversible.

Diagnosis and screening

A single blood test can diagnose congenital hypothyroidism, once it is suspected.  Diagnosis is essential soon after birth, if these children are to have a normal life.  However, not all children have the signs described above, and the disorder may not be suspected at all.

For this reason, newborn screening programs are used.  All newborns have a blood sample taken, and blood levels of either the thyroid hormone thyroxine, or TSH, are measured.  In the USA, for example, newborn screening for congenital hypothyroidism is done in all 50 states (and District of Columbia).  If the first blood sample is taken very early, as happens currently because mothers and babies are being discharged from hospitals early, some children with congenital hypothyroidism may be missed.  A second test after 2 weeks will catch an additional 10-12% of children.

Treatment

Once the diagnosis is made treatment is relatively simple.  The child has to take thyroid hormone tablets, to replace the hormone the body cannot manufacture.  The tablets are not very expensive, but must be taken lifelong.  Thyroid hormone is needed for daily living, and it is unlikely that the thyroid gland will start making it later.  

Children who are diagnosed early and take regular treatment have almost normal growth and development.  Intelligence is within the normal range, and the treatment is quite safe.  Treatment must be guided by repeated laboratory tests, to ensure that the thyroid hormone levels are in the upper normal range.

Last revision: July 15, 2007

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