CONGENITAL HYPOTHYROIDISM (CH)

Congenital hypothyroidism (CH) is the most common congenital endocrine disorder in childhood and is one of the most common preventable causes of mental retardation. In majority of patients, CH is caused by an abnormal development of the thyroid gland (thyroid dysgenesis) that is a sporadic disorder and accounts for 85% of cases and the remaining 15% of cases are caused by dyshormonogenesis.

The clinical features of congenital hypothyroidism are so subtle that many newborn infants remain undiagnosed at birth and delayed diagnosis leads to the most severe outcome of CH, mental retardation, emphasizing the importance of neonatal screening.

The overall incidence of CH ranges from 1 in 3000 to 1 in 4000 newborn infants. The incidence of CH is higher in Hispanic and Asian individuals and lower in black individuals. There is a 2:1 greater incidence in females compared with males and there is an increased risk in infants with Down’s syndrome.

Very early in an unborn baby’s development the thyroid gland moves from the back of the tongue to its normal position in the neck. In some babies this fails to occur, and the gland does not develop at all. In others it is higher in the neck than normal and does not work as well as it should. Dysgenesis is the term that is often used to describe these forms of CHT. Around 80% of babies with CHT have dysgenesis and the risk of a couple having another child with this kind of CHT is low. The more uncommon type, dyshormonogenesis, affects around 20% of babies with CHT. The gland is in the right position but does not produce thyroxine normally because of a ‘production line’ problem. This type can be inherited and there is a risk that the baby’s siblings will also be affected.

If your baby tests positive, his or her condition should be managed by a pediatric endocrinologist or a pediatrician with a special interest in endocrinology (hormone specialist who deals with children) and treatment with levothyroxine (synthetic thyroid hormone, T4) should be started without delay. You only need to treat with T4 (rather than T3) in newborn babies because the body can use the T4 to make T3. The dose is carefully calculated based on factors such as the weight of the baby and will need adjusting regularly as the baby grows. The adjustment is monitored by blood tests that measure thyroid hormone and TSH levels. These tests are carried out every few weeks during the first year of life and every three to six months during infancy and childhood.