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AOP: 188


A descriptive phrase which references both the Molecular Initiating Event and Adverse Outcome.It should take the form “MIE leading to AO”. For example, “Aromatase inhibition leading to reproductive dysfunction” where Aromatase inhibition is the MIE and reproductive dysfunction the AO. In cases where the MIE is unknown or undefined, the earliest known KE in the chain (i.e., furthest upstream) should be used in lieu of the MIE and it should be made clear that the stated event is a KE and not the MIE.  More help

Iodotyrosine deiodinase (IYD) inhibition leading to altered amphibian metamorphosis

Short name
A name that succinctly summarises the information from the title. This name should not exceed 90 characters. More help
IYD inhib alters metamorphosis
The current version of the Developer's Handbook will be automatically populated into the Handbook Version field when a new AOP page is created.Authors have the option to switch to a newer (but not older) Handbook version any time thereafter. More help
Handbook Version v1.0

Graphical Representation

A graphical representation of the AOP.This graphic should list all KEs in sequence, including the MIE (if known) and AO, and the pair-wise relationships (links or KERs) between those KEs. More help
Click to download graphical representation template Explore AOP in a Third Party Tool


The names and affiliations of the individual(s)/organisation(s) that created/developed the AOP. More help

Jennifer H. Olker, Center for Computational Toxicology and Exposure, US EPA, Duluth, MN, USA <>

Jonathan T. Haselman, Center for Computational Toxicology and Exposure, US EPA, Duluth, MN, USA <>

Sigmund J. Degitz, Center for Computational Toxicology and Exposure, US EPA, Duluth, MN, USA <>

Michael W. Hornung, Center for Computational Toxicology and Exposure, US EPA, Duluth, MN, USA <>

Point of Contact

The user responsible for managing the AOP entry in the AOP-KB and controlling write access to the page by defining the contributors as described in the next section.   More help
Arthur Author   (email point of contact)


Users with write access to the AOP page.  Entries in this field are controlled by the Point of Contact. More help
  • Jonathan Haselman
  • Arthur Author


This field is used to identify coaches who supported the development of the AOP.Each coach selected must be a registered author. More help

OECD Information Table

Provides users with information concerning how actively the AOP page is being developed and whether it is part of the OECD Workplan and has been reviewed and/or endorsed. OECD Project: Assigned upon acceptance onto OECD workplan. This project ID is managed and updated (if needed) by the OECD. OECD Status: For AOPs included on the OECD workplan, ‘OECD status’ tracks the level of review/endorsement of the AOP . This designation is managed and updated by the OECD. Journal-format Article: The OECD is developing co-operation with Scientific Journals for the review and publication of AOPs, via the signature of a Memorandum of Understanding. When the scientific review of an AOP is conducted by these Journals, the journal review panel will review the content of the Wiki. In addition, the Journal may ask the AOP authors to develop a separate manuscript (i.e. Journal Format Article) using a format determined by the Journal for Journal publication. In that case, the journal review panel will be required to review both the Wiki content and the Journal Format Article. The Journal will publish the AOP reviewed through the Journal Format Article. OECD iLibrary published version: OECD iLibrary is the online library of the OECD. The version of the AOP that is published there has been endorsed by the OECD. The purpose of publication on iLibrary is to provide a stable version over time, i.e. the version which has been reviewed and revised based on the outcome of the review. AOPs are viewed as living documents and may continue to evolve on the AOP-Wiki after their OECD endorsement and publication.   More help
OECD Project # OECD Status Reviewer's Reports Journal-format Article OECD iLibrary Published Version
This AOP was last modified on May 26, 2024 20:39

Revision dates for related pages

Page Revision Date/Time
Inhibition, Iodotyrosine deiodinase (IYD) September 16, 2017 10:17
Decrease of Thyroidal iodide April 04, 2019 09:00
Thyroid hormone synthesis, Decreased November 04, 2022 09:25
Altered, Amphibian metamorphosis September 02, 2020 11:19
Thyroxine (T4) in serum, Decreased October 10, 2022 08:52
Inhibition, Iodotyrosine deiodinase (IYD) leads to Thyroidal Iodide, Decreased December 03, 2016 16:38
Thyroidal Iodide, Decreased leads to TH synthesis, Decreased June 04, 2018 06:11
Inhibition, Iodotyrosine deiodinase (IYD) leads to T4 in serum, Decreased September 09, 2021 05:27
TH synthesis, Decreased leads to T4 in serum, Decreased October 10, 2022 08:56
T4 in serum, Decreased leads to Altered, Amphibian metamorphosis August 25, 2020 16:43


A concise and informative summation of the AOP under development that can stand-alone from the AOP page. The aim is to capture the highlights of the AOP and its potential scientific and regulatory relevance. More help

This putative adverse outcome pathway describes the linkage between inhibition of iodotyrosine deiodinase (dehalogenase, IYD) and altered amphibian metamorphosis. Initial development of this AOP is based largely on IYD literature of clinical evidence in humans, rat model experiments, and biochemical and genetic analyses. The enzyme IYD catalyzes the recycling of iodide from the byproducts of thyroid hormone (TH) synthesis [monoiodotyrosine (MIT) and diiodotyrosine (DIT)] within the thyroid gland as well as other organs, including liver and kidney. IYD protects against excretion of critical iodide and promotes accumulation of iodide in thyroid follicular cells for TH synthesis, which is especially critical for low iodine diets and low iodine environments (including most freshwater ecosystems). Therefore, failure or chemical inhibition of IYD could reduce TH synthesis, resulting in TH insufficiency in tissues and subsequent altered development. Failure of this enzyme in humans, due to mutations in the IYD gene (DEHAL1), has been shown to have negative developmental consequences, including hypothyroidism, goiter, and mental retardation. In rat exposures with suspected IYD inhibitors, serum T4 and T3 were reduced, thyroid gland size and TSH increased, and weight gain was reduced. Additionally, IYD has been shown to be a potential chemical target for thyroid axis disruption through in vitro inhibition assays with polychlorinated biphenyls, polybrominated diphenyl ethers, agrichemicals, antiparasitics, pharmaceuticals, and food colorants. This molecular initiating event, inhibition of IYD, may have broad taxonomic applicability; IYD genes are highly conserved across a wide range of multicellular organisms with evidence that iodide salvage is important for many species.

AOP Development Strategy


Used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development.The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below. More help


Provides a description of the approaches to the identification, screening and quality assessment of the data relevant to identification of the key events and key event relationships included in the AOP or AOP network.This information is important as a basis to support the objective/envisaged application of the AOP by the regulatory community and to facilitate the reuse of its components.  Suggested content includes a rationale for and description of the scope and focus of the data search and identification strategy/ies including the nature of preliminary scoping and/or expert input, the overall literature screening strategy and more focused literature surveys to identify additional information (including e.g., key search terms, databases and time period searched, any tools used). More help

Summary of the AOP

This section is for information that describes the overall AOP.The information described in section 1 is entered on the upper portion of an AOP page within the AOP-Wiki. This is where some background information may be provided, the structure of the AOP is described, and the KEs and KERs are listed. More help


Molecular Initiating Events (MIE)
An MIE is a specialised KE that represents the beginning (point of interaction between a prototypical stressor and the biological system) of an AOP. More help
Key Events (KE)
A measurable event within a specific biological level of organisation. More help
Adverse Outcomes (AO)
An AO is a specialized KE that represents the end (an adverse outcome of regulatory significance) of an AOP. More help
Type Event ID Title Short name
MIE 1152 Inhibition, Iodotyrosine deiodinase (IYD) Inhibition, Iodotyrosine deiodinase (IYD)
KE 425 Decrease of Thyroidal iodide Thyroidal Iodide, Decreased
KE 277 Thyroid hormone synthesis, Decreased TH synthesis, Decreased
KE 281 Thyroxine (T4) in serum, Decreased T4 in serum, Decreased
AO 1101 Altered, Amphibian metamorphosis Altered, Amphibian metamorphosis

Relationships Between Two Key Events (Including MIEs and AOs)

This table summarizes all of the KERs of the AOP and is populated in the AOP-Wiki as KERs are added to the AOP.Each table entry acts as a link to the individual KER description page. More help

Network View

This network graphic is automatically generated based on the information provided in the MIE(s), KEs, AO(s), KERs and Weight of Evidence (WoE) summary tables. The width of the edges representing the KERs is determined by its WoE confidence level, with thicker lines representing higher degrees of confidence. This network view also shows which KEs are shared with other AOPs. More help

Prototypical Stressors

A structured data field that can be used to identify one or more “prototypical” stressors that act through this AOP. Prototypical stressors are stressors for which responses at multiple key events have been well documented. More help

Life Stage Applicability

The life stage for which the AOP is known to be applicable. More help
Life stage Evidence
Development High

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available. More help
Term Scientific Term Evidence Link
African clawed frog Xenopus laevis Low NCBI

Sex Applicability

The sex for which the AOP is known to be applicable. More help
Sex Evidence
Unspecific High

Overall Assessment of the AOP

Addressess the relevant biological domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and Weight of Evidence (WoE) for the overall AOP as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). More help

Domain of Applicability

Addressess the relevant biological domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context. More help

Essentiality of the Key Events

The essentiality of KEs can only be assessed relative to the impact of manipulation of a given KE (e.g., experimentally blocking or exacerbating the event) on the downstream sequence of KEs defined for the AOP. Consequently, evidence supporting essentiality is assembled on the AOP page, rather than on the independent KE pages that are meant to stand-alone as modular units without reference to other KEs in the sequence. The nature of experimental evidence that is relevant to assessing essentiality relates to the impact on downstream KEs and the AO if upstream KEs are prevented or modified. This includes: Direct evidence: directly measured experimental support that blocking or preventing a KE prevents or impacts downstream KEs in the pathway in the expected fashion. Indirect evidence: evidence that modulation or attenuation in the magnitude of impact on a specific KE (increased effect or decreased effect) is associated with corresponding changes (increases or decreases) in the magnitude or frequency of one or more downstream KEs. More help

Evidence Assessment

Addressess the biological plausibility, empirical support, and quantitative understanding from each KER in an AOP. More help

Known Modulating Factors

Modulating factors (MFs) may alter the shape of the response-response function that describes the quantitative relationship between two KES, thus having an impact on the progression of the pathway or the severity of the AO.The evidence supporting the influence of various modulating factors is assembled within the individual KERs. More help

Quantitative Understanding

Optional field to provide quantitative weight of evidence descriptors.  More help

Considerations for Potential Applications of the AOP (optional)

Addressess potential applications of an AOP to support regulatory decision-making.This may include, for example, possible utility for test guideline development or refinement, development of integrated testing and assessment approaches, development of (Q)SARs / or chemical profilers to facilitate the grouping of chemicals for subsequent read-across, screening level hazard assessments or even risk assessment. More help


List of the literature that was cited for this AOP. More help

Afink, G.; Kulik, W.; Overmars, H.; de Randamie, J.; Veenboer, T.; van Cruchten, A.; Craen, M.; Ris-Stalpers, C. (2008). Molecular characterization of iodotyrosine dehalogenase deficiency in patients with hypothyroidism. Journal of Clinical Endocrinology and Metabolism, 93, 4894-4901.

Fujimoto, K.; Matsuura, K.; Das, B.; Fu, L.; Shi, Y-B. (2012). Direct activation of Xenopus iodotyrosine deiodinase by thyroid hormone receptor in the remodeling intestine during amphibian metamorphosis. Endocrinology, 153, 5082-5089.

Gaupale, T.; Mathi, A.; Ravikuma, A.; Bhargave, S. (2009). Localization and enzyme activity Iodotyrosine dehalogenase 1 during metamorphosis of frog Microhyla ornata. Trends in Comparative Endocrinology and Neurobiology, 1163, 402-406.

Green, W.L. (1971). Effects of 3-nitro-L-tyrosine on thyroid function in the rat: an experimental model for the dehalogenase defect. The Journal of Clinical Investigation, 50, 2474-2484.

Moreno, J.; Klootwijk, W.; van Toor, H.; Pinto, G.; D’Alessandro, M.; Leger, A.; Goudie, D.; Polak, M.; Gruters, A.; Visser, T. (2008). Mutations in the iodotyrosine deiodinase gene and hypothyroidism. The New England Journal of Medicine, 358, 1811-1818

Meinhold, H.; Buchholz, R. (1983). Effects of iodotyrosine deiodinase inhibition on serum concentrations and turnover of diiodotyrosine (DIT) and thyrosine (T4) in the rat. Acta endocrinologica, 103, 521-527.

Phatarphekar, A.; Buss, J.; Rokita, S. (2014). Iodotyrosine deiosinase: a unique flavoprotein present in organisms of diverse phyla. Molecular Biosystems, 10, 86-92.

Shimizu, R.; Yamaguchi, M.; Uramaru, N.; Kuroki, H.; Ohta, S.; Kitamura, S.; Sugihara, K. (2013). Structure-activity relationships of 44 halogenated compounds for iodotyrosine deiodinase-inhibitory activity. Toxicology, 314, 22-29.