DIO1

DIO1
Identifiers
Aliases	DIO1, 5DI, TXDI1, D1, ITDI1, deiodinase, iodothyronine type I, iodothyronine deiodinase 1, THMA2
External IDs	OMIM: 147892; MGI: 94896; GeneCards: DIO1
Enzyme activity
Gene location (Human)
Chr.	Chromosome 1 (human)
End	53,911,086 bp
Gene location (Mouse)
Chr.	Chromosome 4 (mouse)
End	107,164,366 bp
RNA expression pattern
	Top expressed in
	right lobe of thyroid gland; ; kidney tubule; ; liver; ; left lobe of thyroid gland; ; right lobe of liver; ; glomerulus; ; metanephric glomerulus; ; human kidney; ; testicle; ; bronchial epithelial cell;
	Top expressed in
	left lobe of liver; ; islet of Langerhans; ; jejunum; ; crypt of lieberkuhn of small intestine; ; left colon; ; ileum; ; right kidney; ; duodenum; ; epithelium of stomach; ; human kidney;
	More reference expression data
	n/a
Gene ontology
Molecular function	selenium binding; oxidoreductase activity; thyroxine 5'-deiodinase activity;
Cellular component	endoplasmic reticulum membrane; plasma membrane; membrane; integral component of membrane; endoplasmic reticulum;
Biological process	thyroid hormone generation; hormone biosynthetic process; thyroid hormone metabolic process;
	Sources:Amigo / QuickGO
Orthologs
Databases	NCBI: entry; OMA: entry
	1733
	13370
	ENSG00000211452
	ENSMUSG00000034785
	P49895
	Q61153
	NM_000792; NM_001039715; NM_001039716; NM_213593; NM_001324316
	NM_007860
	NP_000783; NP_001034804; NP_001034805; NP_001311245; NP_998758
	NP_031886
	Wikidata
View/Edit Human	View/Edit Mouse

Type I iodothyronine deiodinase is an enzyme that in humans is encoded by the DIO1 gene. This enzyme is a type of iodothyronine deiodinase (EC 1.21.99.3/EC 1.21.99.4), which are enzymes involved in activating and deactivate thyroid hormones by removing iodine atoms from them (called deiodination). This form is distinct in being capable of both activation and inactivation, unlike type II iodothyronine deiodinase which can only activate (EC 1.21.99.4) thyroid hormones, and type III iodothyronine deiodinase which can only deactivate (EC 1.21.99.3) thyroid hormones.

Function

As an (outer ring) thyroxine 5-deiodinase, (EC 1.21.99.4) the DIO1 enzyme is able to catalyze the following reaction:

L-thyroxine + AH₂ → 3,3',5-triiodo-L-thyronine + iodide + A + H⁺

Which converts the less active thyroxine (T₄) into the more active triiodothyronine (T₃) hormone. It is also able to act as an (inner ring) thyroxine 5'-deiodinase, (EC 1.21.99.3), which means it is also able to catalyze:

L-thyroxine + AH₂ → 3,3',5'-triiodo-L-thyronine + iodide + A + H⁺

Which instead produces reverse triiodothyronine (rT₃).

Medical significance

Certain variants in the DIO1 gene have been associated with unusually high levels of rT₃ in blood tests, called Thyroid hormone metabolism, abnormal, 2 (THMA2). However, the effect of this on health, if any, remains unclear.

References

1 2 3 GRCh38: Ensembl release 89: ENSG00000211452 – Ensembl, May 2017
1 2 3 GRCm38: Ensembl release 89: ENSMUSG00000034785 – Ensembl, May 2017
↑ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
↑ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
↑ "DIO1 iodothyronine deiodinase 1". Entrez Gene. NCBI. Retrieved 2026-09-24.
1 2 3 4 5 "Type I iodothyronine deiodinase". uniprot.org. UniProt consortium. Retrieved 2026-09-24.
↑ Köhrle J, Frädrich C (2022-11-20). "Deiodinases control local cellular and systemic thyroid hormone availability". Free Radical Biology and Medicine. 193: 59–79. doi:10.1016/j.freeradbiomed.2022.09.024.
1 2 "THYROID HORMONE METABOLISM, ABNORMAL, 2; THMA2". Online Mendelian Inheritance in Man. Johns Hopkins University. 2022-04-25. Retrieved 2026-09-24.

This article on a gene on human chromosome 1 is a stub. You can help Wikipedia by adding missing information.

[refGRCh38Ensembl-1] 1 2 3 GRCh38: Ensembl release 89: ENSG00000211452 – Ensembl, May 2017

[refGRCm38Ensembl-2] 1 2 3 GRCm38: Ensembl release 89: ENSMUSG00000034785 – Ensembl, May 2017

[3] "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.

[4] "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.

[entrez-5] "DIO1 iodothyronine deiodinase 1". Entrez Gene. NCBI. Retrieved 2026-09-24.

[uniprot-6] 1 2 3 4 5 "Type I iodothyronine deiodinase". uniprot.org. UniProt consortium. Retrieved 2026-09-24.

[7] Köhrle J, Frädrich C (2022-11-20). "Deiodinases control local cellular and systemic thyroid hormone availability". Free Radical Biology and Medicine. 193: 59–79. doi:10.1016/j.freeradbiomed.2022.09.024.

[omim-8] 1 2 "THYROID HORMONE METABOLISM, ABNORMAL, 2; THMA2". Online Mendelian Inheritance in Man. Johns Hopkins University. 2022-04-25. Retrieved 2026-09-24.