Congenital hypothyroidism: Encyclopedia II - Congenital hypothyroidism - Causes

Congenital hypothyroidism - Causes

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 mixture 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.

Congenital hypothyroidism can also occur due to genetic defects of thyroxine or triiodothyronine synthesis within a structurally normal gland. Among specific defects are thyrotropin (TSH) resistance, iodine trapping defect, organification defect, thyroglobulin, and iodotyrosine deiodinase deficiency. In a small proportion of cases of congenital hypothyroidism, the defect is due to a deficiency of thyroid stimulating hormone, either isolated or as part of congenital hypopituitarism.

In some instances, hypothyroidism detected by screening may be transient. The most common cause of this is the presence of maternal antibodies which 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.

Adapted from the Wikipedia article "Causes", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki