What you carry at this position in your DNA and what research says about it.
Platelet Count and Size: 10/10 evidence, 29 publications.
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Sample genotype (not yours): T/T
Lower Platelet Count and Larger Platelet Size
Fewer but larger platelets in circulation are typical for this genetic profile. It also correlates with a slightly higher risk of developing low platelet counts.
What this genotype means: Lower circulating platelet count; Larger average platelet size (MPV); Increased risk of thrombocytopenia.
Sample genotype (not yours): C/C
Typical Platelet Count and Size
Standard platelet counts and typical platelet sizes are characteristic of this genetic profile. It is linked to the lowest risk of developing low platelet counts.
What this genotype means: Typical circulating platelet count; Standard average platelet size; Lowest risk of thrombocytopenia.
Sample genotype (not yours): T/C
Slightly Lower Platelet Count and Larger Platelets
A single T allele is linked to a mild reduction in platelet count and slightly larger platelet size. It also carries a modest increase in the risk of low platelet counts.
What this genotype means: Slightly lower platelet count; Slightly larger average platelet size; Modestly increased risk of thrombocytopenia.
Gene function and biological role
Gene Function: The ARHGEF3 gene encodes a Rho guanine nucleotide exchange factor that plays a critical role in megakaryocyte maturation and platelet formation [1]. It acts as a key regulator of the RhoA signaling pathway, which controls cell shape and cytoskeletal rearrangements during blood cell development [1]. Variations in this gene are strongly linked to differences in how platelets are produced and structured [2]. Understanding ARHGEF3 function helps clarify individual differences in blood cell traits and clotting dynamics [2].
Variant Impact: The rs1354034 variant is a common genetic change located in the promoter region of the ARHGEF3 gene [2]. This variant acts as an expression quantitative trait locus (eQTL), meaning it directly alters the level of ARHGEF3 gene expression in platelets and their precursor cells [2]. Specifically, the T allele is associated with higher gene expression, whereas the C allele leads to lower expression [2]. These expression differences directly influence platelet count and mean platelet volume in the bloodstream [3].
Key Insight: This variant is one of the most powerful genetic regulators of platelet size and count in the human genome, directly altering how megakaryocytes mature into functional platelets.
Location: ARHGEF3. Chromosome 3 · 3p14.3 · 56.8 Mb
Estimated prevalence by population
Global 28.1%; European 15.3%; African 55.8%; East Asian 18.2%; South Asian 23.2%; Americas 29.9%; Ashkenazi 21.8%; Finnish 8.3%; Middle Eastern 28.5%; Amish 22.4%.
Estimated TT genotype frequency.
Global 44.9%; European 47.6%; African 37.8%; East Asian 48.9%; South Asian 49.9%; Americas 49.6%; Ashkenazi 49.8%; Finnish 41.1%; Middle Eastern 49.8%; Amish 49.9%.
Estimated TC genotype frequency.
Global 27.1%; European 37.1%; African 6.4%; East Asian 32.8%; South Asian 26.9%; Americas 20.5%; Ashkenazi 28.4%; Finnish 50.6%; Middle Eastern 21.7%; Amish 27.7%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Platelet Count. Evidence: 10/10. Source: PMID 27863252. Lower Platelet Count.
Mean Platelet Volume. Evidence: 10/10. Source: PMID 27863252. Larger Platelets.
Lymphocyte Count. Evidence: 10/10. Source: PMID 27863252. Typical.
Rare Genetic Disorders
Bleeding & Coagulation Disorders
Thrombocytopenia. Evidence: 8/10. Source: PMID 38064665. Increased Risk.
Showing effects for C/C genotype
Platelet Count. Evidence: 10/10. Source: PMID 27863252. Typical Platelet Count.
Mean Platelet Volume. Evidence: 10/10. Source: PMID 27863252. Typical Platelet Size.
Lymphocyte Count. Evidence: 10/10. Source: PMID 27863252. Higher.
Thrombocytopenia. Evidence: 8/10. Source: PMID 38064665. Typical Risk.
Showing effects for T/C genotype
Lymphocyte Count. Evidence: 10/10. Source: PMID 27863252. Slightly Higher.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Presence of two T alleles at this locus is associated with lower overall platelet counts and a corresponding increase in mean platelet volume [1]. Platelets are the cell fragments responsible for blood clotting, and their size and number are tightly regulated [1]. This genetic variant acts as an expression quantitative trait locus, with the T allele driving higher expression of the ARHGEF3 gene in megakaryocytes, the precursor cells that produce platelets [2]. Higher expression of this gene alters the maturation process of these cells, resulting in larger but fewer platelets being released into the bloodstream [2]. Consequently, this genotype is linked to an increased risk of gestational and general thrombocytopenia, a condition characterized by abnormally low platelet levels [3]. While this genetic tendency is common and usually does not cause active bleeding issues on its own, it can influence clinical blood test interpretations [1]. Understanding this baseline genetic profile helps contextualize routine complete blood count results [1].
Lower circulating platelet count; Larger average platelet size (MPV); Increased risk of thrombocytopenia.
Sample genotype: CC (Homozygous)
Possessing two copies of the C allele at this locus is associated with typical platelet counts and standard mean platelet volume [1]. The C allele is linked to lower expression of the ARHGEF3 gene in megakaryocytes, allowing for standard platelet maturation and release [2]. As a result, individuals with this genotype tend to have a higher, more optimal concentration of platelets in circulation compared to T allele carriers [1]. This genotype also confers the lowest genetic risk for thrombocytopenia, a condition of low platelet counts [3]. Having a typical number of standard-sized platelets supports healthy blood clotting and vascular homeostasis [1]. This genetic profile represents the baseline standard for platelet parameters in complete blood counts [1]. It is a highly stable genetic profile that minimizes risk for platelet-related blood variations [1].
Typical circulating platelet count; Standard average platelet size; Lowest risk of thrombocytopenia.
Sample genotype: TC (Heterozygous)
A heterozygous T/C genotype is linked to a moderate reduction in platelet count and an increase in mean platelet volume [1]. This intermediate effect occurs because the T allele increases the expression of the ARHGEF3 gene in platelet-producing megakaryocytes, altering their normal maturation [2]. The resulting platelets tend to be slightly larger but fewer in number compared to those with the C/C genotype [2]. This genetic profile is also associated with a slightly elevated risk of thrombocytopenia, particularly during physiological stressors like pregnancy [3]. Because platelets play a vital role in blood clotting, these subtle shifts in cell size and count can influence overall clotting dynamics [1]. For most individuals, this variation remains within the normal physiological range and does not lead to clinical symptoms [1]. It is primarily useful for understanding personal baselines in routine blood panels [1].
Slightly lower platelet count; Slightly larger average platelet size; Modestly increased risk of thrombocytopenia.
Variants with shared genetic architecture
rs1613662 · GP6 Gene · Chr 19 · Venous Thrombosis Risk
rs6065 · GP1BA Gene · Chr 17 · Platelet Function and Stroke
rs6141 · THPO Gene · Chr 3 · Platelet Levels and Bleeding
New gene functions in megakaryopoiesis and platelet formation.
The Allelic Landscape of Human Blood Cell Trait Variation and Links to Common Complex Disease.
The Polygenic and Monogenic Basis of Blood Traits and Diseases.
Genetic basis of pregnancy-associated decreased platelet counts and gestational thrombocytopenia.
Content updated August 2026.
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