GPX1 rs1050450 (Pro198Leu): Selenium, Iodine, and Thyroid Biology

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 the genes behind antioxidant status and micronutrient metabolism. Browse all Blood Testing & Biomarkers education

The rs1050450 variant sits inside GPX1, the gene for glutathione peroxidase 1 — one of the body's most important antioxidant enzymes. Because GPX1 depends on selenium, and because selenium and iodine are both essential to healthy thyroid biology, people searching for the effect of the "G" allele at rs1050450 are usually asking a deeper question: how do my antioxidant genes interact with iodine and thyroid function?

This article explains what GPX1 does, what the rs1050450 (Pro198Leu) variant actually changes, and how antioxidant genetics connect to iodine metabolism. It is educational, not a diagnosis.

What GPX1 does and why selenium matters

Glutathione peroxidase 1 (GPX1) is a selenoenzyme: it uses a selenium-containing amino acid, selenocysteine, at its active site to neutralize hydrogen peroxide and other reactive oxygen species. This is a housekeeping antioxidant found throughout the body, protecting cells from oxidative damage.

Because GPX1 requires selenium to function, its activity tracks closely with selenium status. When selenium is low, GPX1 activity falls; when selenium is adequate, the enzyme works efficiently. That dependency is what links a single antioxidant gene to a broader nutritional and hormonal picture.

The rs1050450 variant (Pro198Leu) explained

The variant at rs1050450 is most often described as Pro198Leu, a change at amino acid position 198 of the GPX1 protein. On the coding strand it is a C-to-T substitution; reported on the opposite DNA strand, the reference "G" allele corresponds to proline (Pro198) and the "A" allele to leucine (Leu198).

The proline-associated form (the "G"/C reference version) is the more common variant in most populations. The leucine-associated form (the "A"/T allele) has been studied for its links to lower glutathione peroxidase activity and, in some research, a blunted rise in enzyme activity when selenium intake increases. In other words, the variant may influence how well your antioxidant system responds to the selenium you consume.

How antioxidant genes connect to iodine and thyroid biology

The thyroid gland is a hotspot for oxidative activity. To build thyroid hormone, the gland uses hydrogen peroxide to attach iodine to thyroglobulin — a process that inevitably generates reactive oxygen species. Selenoenzymes like GPX1 help keep that oxidative byproduct in check, which is one reason the thyroid holds some of the highest selenium concentrations in the body.

Iodine and selenium therefore work as partners: iodine is the raw material for thyroid hormone, and selenium-dependent enzymes protect the tissue and help convert hormone into its active form. The deiodinase enzymes (DIO1 and DIO2), which convert the storage hormone T4 into active T3, are themselves selenoproteins. A variant that shifts antioxidant capacity sits upstream of this entire iodine-handling system.

What the research shows

Studies of Pro198Leu have connected the leucine allele to reduced GPX1 enzyme activity in several tissues and to differences in antioxidant response to selenium supplementation. Research has also examined the variant in relation to oxidative-stress-related conditions, though findings vary by population and no single genotype is deterministic.

Importantly, genotype is only one input. Selenium and iodine intake, overall diet, and other genes in the selenoprotein family all shape the final biological outcome. A named variant like rs1050450 describes a tendency, not a fixed result.

What your genetic results can and cannot tell you

A pathway-level genetic test can show you which version of GPX1 you carry and place it within your broader antioxidant and micronutrient-handling biology. The Precision Peptide Genetic Test analyzes 14 pathways, 49 peptides, 150+ genetic insights, mapping variants like rs1050450 in the context of the pathways they influence rather than as isolated data points.

What it will not do is diagnose a thyroid condition, measure your iodine status, or tell you what to take. Genetics is a guide, not a guarantee. As the PlexusDx principle puts it: the test tells you about your biology — it does not tell you what to put in your body. Iodine and selenium intake decisions belong with a qualified healthcare provider who can order the right bloodwork.

Frequently Asked Questions

Does rs1050450 affect my iodine levels directly?

No. rs1050450 sits in GPX1, an antioxidant gene, and does not set your iodine level. It may influence how efficiently selenium-dependent enzymes protect thyroid tissue, and iodine and selenium work together in thyroid biology. Iodine status is measured through diet review and bloodwork, not genotype.

Is the leucine (Leu198) allele bad?

Not inherently. The leucine allele at rs1050450 has been associated in research with somewhat lower glutathione peroxidase activity, but a variant is a tendency, not a verdict. Selenium intake, overall diet, and other selenoprotein genes all shape outcomes. Many people carry this allele with no clinical consequence.

Should I take selenium if I carry this variant?

That is a decision for a qualified healthcare provider, not a genetic result. Selenium has a narrow safe range and excess can be harmful. A test can show your GPX1 variant and antioxidant-pathway context, but supplement choices should follow clinical evaluation and appropriate blood testing.

Can genetic testing diagnose a thyroid problem?

No. A pathway-level genetic test does not diagnose, treat, or predict thyroid disease. It provides context about antioxidant and micronutrient-handling pathways, including variants like rs1050450. Diagnosing thyroid conditions requires thyroid function bloodwork and evaluation by a licensed clinician.

Curious how your own antioxidant and micronutrient pathways are built? Take the Precision Peptide Genetic Test to see where variants like rs1050450 fall across your 14 mapped biological pathways — the "test before you invest" approach to precision wellness.

This article is part of the PlexusDx Education Hub. Browse all Blood Testing & Biomarkers education

Peptide testing disclaimer: 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.