Molecular Analysis of Mutated Thyroid Peroxidase Detected in Patients with Total Iodide Organification Defects

Abstract

Molecular analysis of mutated thyroid peroxidase detected in patients with total iodide organification defects Bikker, H.; Baas, F.; de Vijlder, J.J.M. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. ABSTRACTWild-type and mutant thyroid peroxidase (TPO) was expressed in a Semliki Forest Virus (SFV)-based transient expression system in Chinese hamster ovary-K1 cells. Twenty four hours after transfection, proteins immunoreactive with TPO antibodies could be detected on a Western blot. Peroxidase activity was assayed using both the guaiacol and the I 3 Ϫ assay. Addition of hematin was necessary to obtain enzymatic active TPO. Thyroid peroxidase complementary DNA constructs containing mutations originally found in patients with hereditary congenital hypothyroidism caused by total iodide organification defects were analyzed using these techniques. In all cases TPO was expressed as shown by Western blotting and immunostaining. Enzymatic activity (measured by guaiacol and iodide oxidation assay) was below the detection level in four out of five mutants. The only mutant yielding TPO with enzymatic activity was G 1858 A (Gly 590 Ser). However, the mutation could affect splicing of TPO messenger RNA, leading to inactive TPO, because it is located at the exon 10/intron 10 border.

High prevalence of thyroid peroxidase gene mutations in patients with thyroid dyshormonogenesis

“…This short amino acid sequence is partly conserved among other mammalian peroxidases, as shown in Table 3. Several other mutations causing TIOD have been identified in close proximity by other groups -I447F, Y453D, L458P, R491H, G493S, and P499L (13,19,20,22,25). Exons 8, 9 and 10 encode for the catalytic part of the enzyme and are the most frequent locations of inactivating mutations.…”

“…The TPO gene spans over 150 kb on the short arm of chromosome 2, locus 2p25, and consists of 17 exons (9,10). Published molecular genetic studies suggest that TPO gene mutations are one of the most common causes of thyroid dyshormonogenesis, with several different inactivating mutations being identified in patients with total iodide organification defects (TIOD; (7,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)). The inheritance is autosomal recessive (16,29).…”

Genetic analysis of thyroid peroxidase (<i>TPO</i>) gene in patients whose hypothyroidism was found in adulthood in West Bengal, India

“…We analysed non-parametric variables by Mann-Whitney U test. All tests were done using TPO catalyzes the iodination and subsequent coupling of tyrosine residues in thyroglobulin, resulting in the synthesis of the thyroid hormones T4 and T3 [13]. The human TPO gene (GenBank Accesion # NT_033000) is located on chromosome 2p25 and spans approximately 150 Kb, containing 17 exons [14].…”

Two novel missense mutations in the thyroid peroxidase gene, R665W and G771R, result in a localization defect and cause congenital hypothyroidism

“…The most prevalent cause of congenital defects in thyroid hormone synthesis is believed to be TPO deficiency (10). Mutations in the TPO gene described up to now have been classified as frameshift mutations (11 -18), missense mutations (13, 15 -17, 19), mutations affecting splicing (13,17,20), nonsense mutations (17,21), and gene deletion (22).…”