Pendred's Syndrome was described in 1896 by Pendred but discovering its genetic basis took a century.
Inheritance: autosomal recessive
Genetic locus: PDS gene (SLC26A4) on chromosome 7 (7q22.31.1), which encodes the protein pendrin
Function of pendrin: ion transport of iodide, chloride and bicarbonate
Clinical findings:
(1) bilateral sensorineural hearing loss
(2) goiter with defective organification of iodide. The goiter varies in severity since there are other proteins involved in iodine transport that may partially compensate for the defect.
The perchlorate discharge test involves administration of radioiodine followed a little while later by potassium perchlorate (KCl04). Normally absorbed iodide enters the thyroid follicular cell, is incorporated into thyroid hormone and is then secreted into the colloid. If pendrin is defective this "organification" of iodide is impaired. Perchlorate inhibits the iodide trapping that keeps the iodide within the follicular cell and allows it to escape. A positive perchlorate discharge test is when greater than 10% of an administered dose of radioiodine escapes from the thyroid gland after perchlorate is given. Several conditions including Pendred's Syndrome are associated with a positive perchlorate discharge test.
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