Thyroid peroxidase (TPO) is responsible for the oxidation of I- to I2. In addition, thyroid peroxidase catalyzes the organification of I2 into thyroglobulin and the coupling of formed DIT/MIT molecules.
Synthesis of thyroid hormones occurs in the follicular lumen, where thyroglobulin and I- molecules are extruded. Here, via reactions catalyzed by thyroid peroxidase, thyroid hormones are synthesized. Following follicular cell simulation, thyroglobulin (with attached hormones), is brought back into the cell, T4/T3 are cleaved from thyroglobulin, and the hormones are exported from the cell.
Gaitonde et al. present the epidemiology of hypothyroidism. They report that one in 300 persons in the United States has hypothyroidism, with prevalence increasing with age and female gender. The most common cause of hypothyroidism in the United States is autoimmune thyroid disease.
Ozbek et al. investigate the genetic mutations in the thyroid oxidase gene that lead to congenital hypothyroidism. They report that over 60 different mutations have been described in the TPO gene which may lead to hypothyroidism.
Illustration A displays the process of thyroid hormone synthesis.
Answer 1: Thyroid deiodinase is responsible for recycling (deiodination) of MIT and DIT.
Answer 3: 5-deiodinase is responsible for the synthesis of T3 from T4 molecules.
Answer 4: Perchlorate is a chemical that inhibits iodine from entering follicular cells.
Answer 5: Propylthiouracil is a chemical that inhibits thyroid peroxidase.
Gaitonde DY, Rowley KD, Sweeney LB. Hypothyroidism: an update. Am Fam Physician. 2012 Aug 1;86(3):244-51.
PMID:22962987 (Link to Abstract)
Ozbek MN, Uslu AB, Onenli-Mungan N, Yuksel B, Pohlenz J, Topaloglu AK. Thyroid peroxidase gene mutations causing congenital hypothyroidism in three Turkish families. J Pediatr Endocrinol Metab. 2009 Nov;22(11)
PMID:20101889 (Link to Abstract)
USMLE World Step 1 QBank Question #770. Copyright © USMLEWorld, LLC 2012