Congenital Hypothyroidism - Etiology

Etiology

Around the world, the most common cause of congenital hypothyroidism is iodine deficiency, but in most of the developed world and areas of adequate environmental iodine, cases are due to a combination of known and unknown causes. Most commonly there is a defect of development of the thyroid gland itself, resulting in an absent (athyreosis) or underdeveloped (hypoplastic) gland. A hypoplastic gland may develop higher in the neck or even in the back of the tongue. A gland in the wrong place is referred to as ectopic, and an ectopic gland at the base or back of the tongue is a lingual thyroid. Some of these cases of developmentally abnormal glands result from genetic defects, and some are "sporadic," with no identifiable cause. One Japanese study found a statistical correlation between certain organochlorine insecticides and dioxin-like chemicals in the milk of mothers who had given birth to infants with congenital hypothyroidism.

In some instances, hypothyroidism detected by screening may be transient. One common cause of this is the presence of maternal antibodies that temporarily impair thyroid function for several weeks.

Cretinism is an old term for the state of mental and physical retardation resulting from untreated congenital hypothyroidism, usually due to iodine deficiency from birth because of low iodine levels in the soil and local food sources. The term, like so many other 19th century medical terms, acquired pejorative connotations as it became used in lay speech. It is now rarely used by physicians.