Genetic regulation of thyroid development

Defects in any of the essential steps in thyroid development or thyroid hor mone synthesis may result in morphologic abnormalities and, impaired hormon ogenesis. These defects can be partial or complete, leading to varying degr ees of hypothyroidism. Morphologic, alterations associated with congenital hypothyroidism include the absence of detectable thyroid tissue, ectopic, t issue, thyroid hypoplasia, or a goitrous thyroid. However, in some patients with hypothyroidism, the thyroid is of normal size. This article focuses o n defects in thyroid development. Recent insights into the developmental re gulation: of the caloitonin-producing C cells will not be discussed, and de fects in hormone synthesis are discussed in an accompanying article [1]. (C ) 2001 Lippincott Williams & Wilkins, Inc.