What you carry at this position in your DNA and what research says about it.
Iron and Hemoglobin Levels: 10/10 evidence, 21 publications.
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Sample genotype (not yours): G/G
Lower Iron and Hemoglobin Levels
Two copies of the G allele are linked to lower circulating iron levels and smaller red blood cells. This genetic profile increases the likelihood of developing iron deficiency under dietary restriction.
What this genotype means: Lower circulating serum iron; Smaller red blood cell volume; Increased susceptibility to iron deficiency.
Sample genotype (not yours): A/A
Optimal Iron and Hemoglobin Levels
Two copies of the A allele are linked to higher circulating iron levels and larger red blood cells. This profile provides natural protection against iron deficiency.
What this genotype means: Higher circulating serum iron; Larger red blood cell volume; Reduced risk of iron-deficiency anemia.
Sample genotype (not yours): G/A
Typical Iron and Hemoglobin Levels
One copy of each allele results in intermediate iron levels and standard red blood cell characteristics. This balanced profile generally supports typical iron absorption and oxygen transport.
What this genotype means: Standard iron absorption; Typical red blood cell size; Average hemoglobin levels.
Gene function and biological role
Gene Function: The TMPRSS6 gene encodes matriptase-2, a transmembrane serine protease that plays a critical role in maintaining systemic iron homeostasis [1]. Matriptase-2 acts as a negative regulator of hepcidin, a liver-derived hormone that controls systemic iron availability by degrading the iron exporter ferroportin [1]. When matriptase-2 is active, it suppresses hepcidin expression, allowing increased dietary iron absorption in the gut and the release of stored iron into the bloodstream [2]. Genetic variations that alter matriptase-2 activity can significantly impact circulating iron levels, red blood cell characteristics, and overall susceptibility to iron-deficiency anemia [3].
Variant Impact: The rs4820268 variant is a synonymous single nucleotide polymorphism located in exon 13 of the TMPRSS6 gene. Although it does not change the encoded aspartic acid amino acid at position 512, this variant is in strong linkage disequilibrium with functional variants that influence matriptase-2 expression and activity [4]. The G allele of this variant is strongly associated with higher hepcidin expression, which leads to reduced iron absorption and lower serum iron concentrations [5]. Conversely, the major A allele is linked to more efficient matriptase-2 function, resulting in lower hepcidin levels and higher circulating iron [6].
Key Insight: Even though this genetic change is synonymous and does not alter the protein sequence directly, it is one of the strongest genetic predictors of normal variation in human iron levels and red blood cell size.
Location: TMPRSS6. Chromosome 22 · 22q12.3 · 37.1 Mb
Estimated prevalence by population
Global 18.3%; European 21.3%; African 7.2%; East Asian 28.5%; South Asian 32.0%; Americas 26.6%; Ashkenazi 20.0%; Finnish 19.0%; Middle Eastern 20.8%; Amish 15.6%.
Estimated GG genotype frequency.
Global 46.8%; European 49.7%; African 39.3%; East Asian 49.8%; South Asian 49.1%; Americas 50.0%; Ashkenazi 49.4%; Finnish 49.2%; Middle Eastern 49.6%; Amish 47.8%.
Estimated GA genotype frequency.
Global 34.9%; European 29.0%; African 53.5%; East Asian 21.7%; South Asian 18.9%; Americas 23.5%; Ashkenazi 30.6%; Finnish 31.8%; Middle Eastern 29.6%; Amish 36.5%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Iron Levels. Evidence: 6/10. Source: PMID 19084217. Lower Iron Levels.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 28017375. Lower Hemoglobin.
Red Blood Cell Size. Evidence: 6/10. Source: PMID 19853236. Smaller Red Cells.
Diabetes & Glycemic Traits
Blood Sugar Control. Evidence: 6/10. Source: PMID 28898252. Higher HbA1c.
Organ Systems
Liver Function & Disease
Liver Fat. Evidence: 5/10. Source: PMID 32247823. Higher Liver Fat.
Showing effects for A/A genotype
Iron Levels. Evidence: 6/10. Source: PMID 19084217. Higher Iron Levels.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 28017375. Higher Hemoglobin.
Red Blood Cell Size. Evidence: 6/10. Source: PMID 19853236. Larger Red Cells.
Blood Sugar Control. Evidence: 6/10. Source: PMID 28898252. Lower HbA1c.
Liver Fat. Evidence: 5/10. Source: PMID 32247823. Lower Liver Fat.
Showing effects for G/A genotype
Iron Levels. Evidence: 6/10. Source: PMID 19084217. Typical Iron Levels.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 28017375. Typical Hemoglobin.
Red Blood Cell Size. Evidence: 6/10. Source: PMID 19853236. Typical Red Cells.
Blood Sugar Control. Evidence: 6/10. Source: PMID 28898252. Typical HbA1c.
Liver Fat. Evidence: 5/10. Source: PMID 32247823. Typical Liver Fat.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Circulating iron levels are typically lower in individuals with this genotype due to increased baseline expression of hepcidin, which restricts iron absorption in the gut [1]. Research indicates that each copy of the G allele significantly reduces serum iron concentrations and hemoglobin levels [2]. Red blood cells also tend to be smaller in volume and contain less hemoglobin overall [3]. While this genotype does not cause severe clinical disorders on its own, it represents a predisposing factor for iron-deficiency anemia when dietary iron intake is low or during periods of increased iron demand [4]. Additionally, this genetic profile is associated with slightly higher HbA1c levels, which can subtly influence blood sugar assessments [5].
Lower circulating serum iron; Smaller red blood cell volume; Increased susceptibility to iron deficiency.
Sample genotype: AA (Homozygous)
Efficient iron absorption is a key characteristic of this genotype, driven by lower baseline levels of the iron-regulatory hormone hepcidin [1]. Individuals with this profile tend to have higher serum iron concentrations and robust hemoglobin levels [2]. Red blood cells are typically larger in volume and carry more oxygen-binding hemoglobin [3]. This genetic makeup provides a natural buffer against iron-deficiency anemia, making it easier to maintain healthy iron stores even during periods of physical exertion or lower dietary iron intake [4]. Furthermore, this genotype is associated with slightly lower HbA1c levels and lower liver fat accumulation [5].
Higher circulating serum iron; Larger red blood cell volume; Reduced risk of iron-deficiency anemia.
Sample genotype: GA (Heterozygous)
Balanced iron homeostasis is typical for individuals carrying one G allele and one A allele. Matriptase-2 enzyme activity remains moderate, allowing for standard regulation of hepcidin and steady dietary iron absorption [1]. Serum iron levels, hemoglobin concentrations, and red blood cell volumes generally fall within the average range for the population [2]. While there is a modest reduction in iron parameters compared to the A/A genotype, the presence of a single A allele helps buffer against the more pronounced iron-lowering effects seen in G/G homozygotes [3]. Standard dietary habits are usually sufficient to maintain healthy iron stores under normal physiological conditions [4].
Standard iron absorption; Typical red blood cell size; Average hemoglobin levels.
Variants with shared genetic architecture
rs855791 · TMPRSS6 Gene · Chr 22 · Iron and Anemia Risk
rs2413450 · TMPRSS6 Gene · Chr 22 · Red Blood Cell Health
rs7385804 · TFR2 Gene · Chr 7 · Iron Levels
Variants in TF and HFE explain approximately 40% of genetic variation in serum-transferrin levels.
A genome-wide association analysis of serum iron concentrations.
Sequence variants in three loci influence monocyte counts and erythrocyte volume.
Content updated August 2026.
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