Thyroid peroxidase

It is an enzyme expressed mainly in the thyroid where it is secreted into colloid.

It is encoded by the TPO gene.

It oxidizes iodide ions to form iodine atoms for addition onto tyrosine residues on thyroglobulin for the production of thyroxine (T4) or triiodothyronine (T3), the thyroid hormones.

TPO is stimulated by TSH, which upregulates gene expression.

TPO is inhibited by the thioamide drugs, such as propylthiouracil and methimazole.

It is a frequent epitope of autoantibodies in autoimmune thyroid disease.

Such antibodies being called anti-thyroid peroxidase antibodies.

Anti-thyroid peroxidase antibodies area is most commonly associated with Hashimoto’s thyroiditis, and an antibody titer can be used to assess disease activity in patients that have developed such antibodies.

The expression of thyroid peroxidase (TPO) is lost in papillary thyroid carcinoma.

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