Thyroid dysgenesis is a cause of

congenital hypothyroidism Congenital hypothyroidism (CH) is thyroid hormone deficiency present at birth. If untreated for several months after birth, severe congenital hypothyroidism can lead to growth failure and permanent intellectual disability. Infants born with cong ...

where the

thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thy ...

is missing, ectopic, or severely underdeveloped. It should not be confused with

iodine deficiency Iodine deficiency is a lack of the trace element iodine, an essential nutrient in the diet. It may result in metabolic problems such as goiter, sometimes as an endemic goiter as well as congenital iodine deficiency syndrome due to untreated cong ...

, or with other forms of

, such as

thyroid dyshormonogenesis Thyroid dyshormonogenesis is a rare condition due to genetic defects in the synthesis of thyroid hormones. It is due to either deficiency of thyroid enzymes, inability to concentrate, or ineffective binding. Signs and symptoms Patients develop h ...

, where the thyroid is present but not functioning correctly. Congenital hypothyroidism caused by thyroid dysgenesis can be associated with

PAX8 Paired box gene 8, also known as PAX8, is a protein which in humans is encoded by the ''PAX8'' gene. Function This gene is a member of the paired box (PAX) family of transcription factors. Members of this gene family typically encode proteins w ...

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Ectopic thyroid

An ''ectopic thyroid'', also called ''accessory thyroid gland'', is a form of thyroid dysgenesis in which an entire or parts of the thyroid located in another part of the body than what is the usual case. A completely ectopic thyroid gland may be located anywhere along the path of the descent of the thyroid during its embryological development, although it is most commonly located at the base of the tongue, just posterior to the foramen cecum of the tongue. In this location, an aberrant or ectopic thyroid gland is known as a ''lingual thyroid''. If the thyroid fails to descend to even higher degree, then the resulting final resting point of the thyroid gland may be high in the neck, such as just below the

hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical vertebr ...

. emedicine > Embryology of the Thyroid and Parathyroids > Thyroid Embryology Clinical Correlations
By David J Kay and Arlen D Meyers. Updated: Jan 14, 2010 Parts of ectopic thyroid tissue ("accessory thyroid tissue") can also occur, and arises from remnants of the

thyroglossal duct The thyroglossal duct is an embryology, embryological anatomical structure forming an open connection between the initial area of development of the thyroid gland and its final position. It is located exactly mid-line, between the anterior 2/3 and ...

, and may appear anywhere along its original length. Accessory thyroid tissue may be functional, but is generally insufficient for normal function if the main thyroid gland is entirely removed. Lingual thyroid is 4-7 times more common in females, with symptoms developing during puberty, pregnancy or menopause. Lingual thyroid may be asymptomatic, or give symptoms such as

dysphagia Dysphagia is difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, in some contexts it is classified as a disease#Terminology, condition in its own right. It may be a sensation that suggests difficulty in the passag ...

(difficulty swallowing),

dysphonia A hoarse voice, also known as dysphonia or hoarseness, is when the voice involuntarily sounds breathy, raspy, or strained, or is softer in volume or lower in pitch. A hoarse voice, can be associated with a feeling of unease or scratchiness in the ...

(difficulty talking) and

dyspnea Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathing, breathe well enough. The American Thoracic Society defines it as "a subjective experience of brea ...

(difficulty breathing).

References

External links

{{Congenital endocrine disorders Congenital disorders of endocrine system Thyroid