Health Effects of the rs225014 (DIO2 Thr92Ala) C Allele

Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

This article is part of the PlexusDx Education Hub — your resource for evidence-based guidance on hormones & fertility. Browse all Hormones & Fertility education

The single-nucleotide polymorphism rs225014 sits in the DIO2 gene and produces the well-studied Thr92Ala variant, in which the amino acid threonine is replaced by alanine at position 92 of the type 2 deiodinase enzyme. The "C" allele codes for the alanine (Ala92) version. Because DIO2 helps convert thyroid hormone into its active form inside tissues, researchers have looked closely at what carrying this variant may mean for metabolism, joints, and well-being.

What DIO2 and the Thr92Ala variant do

The thyroid mainly releases thyroxine (T4), a relatively inactive prohormone. To act on cells, T4 must be converted to triiodothyronine (T3), and the type 2 deiodinase enzyme encoded by DIO2 performs much of that conversion inside tissues such as the brain, pituitary, and skeletal muscle. The Thr92Ala substitution created by the rs225014 C allele changes the enzyme's structure. Laboratory studies have reported reduced or altered enzyme activity and changes in where the protein localizes inside the cell, which could, in theory, lower local T3 availability in certain tissues even when blood thyroid levels look normal.

Health associations studied for the C allele

The Thr92Ala variant was first identified in research on insulin resistance and later linked, in some studies, to type 2 diabetes risk and to osteoarthritis, where DIO2 is expressed in cartilage. Additional work has explored associations with bone metabolism and mental well-being. It is important to read these findings carefully: associations are statistical, often modest, and not always replicated across populations. Carrying the C allele is common and does not mean a person has or will develop any of these conditions — it describes a probabilistic tendency studied at the group level, not an individual diagnosis.

Thyroid hormone, well-being, and the T3 question

The most debated question involves people treated for hypothyroidism with levothyroxine (synthetic T4). Some studies have asked whether Thr92Ala carriers report more residual symptoms — fatigue, low mood, or cognitive complaints — on T4-only therapy, on the theory that reduced local conversion could leave certain tissues relatively under-supplied with T3. The evidence remains mixed and is not considered strong enough to guide treatment on its own. Any decision about thyroid therapy belongs with a qualified healthcare provider who can review symptoms, lab results, and the whole clinical picture.

Why one variant is only part of the picture

Thyroid hormone metabolism depends on far more than a single SNP. Iodine and selenium status, other deiodinase genes, autoimmune activity, medications, and overall health all shape how the system behaves. A variant like rs225014 is one small tile in a large mosaic. This is why genetic information is best understood as context that adds nuance to a clinical evaluation, rather than a standalone answer about how a person feels or functions.

What a genetic test can and can't tell you

A genetic test provides pathway-level context about your biology, not a diagnosis or a treatment plan. The Precision Peptide Genetic Test analyzes 14 pathways, 49 peptides, 150+ genetic insights across peptide-related biological pathways. Variants such as DIO2 Thr92Ala (rs225014) show how a single change in an enzyme can influence a whole signaling system, but a wellness test does not tell you what to put in your body. It gives you information to discuss with a qualified provider — genetics as a guide, not a guarantee.

Frequently Asked Questions

What is the rs225014 C allele?

The rs225014 C allele codes for the alanine (Ala92) version of the DIO2 Thr92Ala variant, which swaps threonine for alanine in the type 2 deiodinase enzyme. This enzyme converts thyroid hormone T4 into active T3 inside tissues, so researchers study how the variant may affect local hormone activity.

Does carrying this variant mean I have a health problem?

No. The Thr92Ala C allele is common and describes a statistical tendency studied in groups, not an individual diagnosis. Associations with insulin resistance, osteoarthritis, and well-being are often modest and inconsistently replicated. Carrying it does not mean you have or will develop any of these conditions.

Does rs225014 predict how I will respond to thyroid medication?

No. Some studies explore whether carriers report more residual symptoms on T4-only therapy, but the evidence is mixed and not strong enough to guide treatment. A wellness genetic test does not predict drug response. Any thyroid treatment decision should be made with a qualified healthcare provider.

Can I change my genetics around thyroid conversion?

You cannot change your DNA, but thyroid hormone metabolism is influenced by many factors, including nutrient status, other genes, and overall health. Genetic insight is context, not destiny. Work with a qualified provider who can consider your symptoms, labs, and history together rather than any single variant.

Curious how your genetics fit into the bigger picture? The Precision Peptide Genetic Test offers pathway-level insight you can bring to a conversation with your healthcare provider — genetics as a guide, not a guarantee.

This article is part of the PlexusDx Education Hub. Browse all Hormones & Fertility education

The Precision Peptide Genetic Test analyzes how your genes influence peptide-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use. Consult a qualified healthcare provider before beginning any peptide protocol.

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.