What you carry at this position in your DNA and what research says about it.
Platelet Size: 8/10 evidence, 9 publications.
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Sample genotype (not yours): C/C
Typical Platelet Size
Two copies of the C allele are associated with typical platelet size and a standard baseline for clotting activity. While your platelet size is typical, some studies suggest a lower survival rate following an ischemic stroke compared to T allele carriers.
What this genotype means: Typical mean platelet volume; Slightly higher platelet count; Standard baseline cardiovascular risk.
Sample genotype (not yours): C/T
Larger Platelets but Better Stroke Survival
Carrying one copy of the T allele is linked to larger, more active platelets, which can slightly increase clotting activity. Paradoxically, this genotype is also associated with a significantly higher survival rate one year after a stroke.
What this genotype means: Increased mean platelet volume; Slightly lower platelet count; Improved post-stroke survival rate.
Sample genotype (not yours): T/T
Larger Platelet Size
Two copies of the T allele are linked to significantly larger, more active platelets, which can increase clotting activity. This genotype is also associated with a lower risk of arterial stiffness and better survival rates after a stroke.
What this genotype means: Significantly increased mean platelet volume; Lower overall platelet count; Improved post-stroke survival rate.
Gene function and biological role
Gene Function: CFAP251, previously known as WDR66, encodes a protein associated with cilia and flagella that is also highly expressed in megakaryocytes, the precursor cells that produce platelets [1]. Genetic variations within this gene are among the strongest known determinants of mean platelet volume in human populations [2]. By influencing how megakaryocytes mature and release platelets, this gene plays a central role in determining the physical characteristics of circulating blood cells [1]. These physical traits directly impact platelet activation, clotting speed, and overall vascular dynamics [2].
Variant Impact: The rs7961894 variant is located within an intron of the CFAP251 gene on chromosome 12. The T allele of this variant is strongly associated with an increase in mean platelet volume, resulting in larger and more active platelets [2]. Conversely, the C allele is linked to a slightly higher overall platelet count but smaller individual platelet size [1]. This single nucleotide change explains a significant portion of the natural genetic variation in platelet size and function observed across different ancestries [2].
Key Insight: While larger platelets are traditionally linked to higher cardiovascular risk, carriers of the T allele paradoxically show significantly better survival rates one year after an ischemic stroke.
Location: CFAP251. Chromosome 12 · 12q24.31 · 121.9 Mb
Estimated prevalence by population
Global 86.2%; European 80.0%; African 96.1%; East Asian > 99.9%; South Asian 93.8%; Americas 85.1%; Ashkenazi 81.3%; Finnish 81.9%; Middle Eastern 87.5%; Amish 73.5%.
Estimated CC genotype frequency.
Global 13.1%; European 18.9%; African 3.9%; East Asian < 0.1%; South Asian 6.1%; Americas 14.3%; Ashkenazi 17.8%; Finnish 17.2%; Middle Eastern 12.1%; Amish 24.4%.
Estimated CT genotype frequency.
Global 0.7%; European 1.1%; African < 0.1%; East Asian < 0.1%; South Asian 0.1%; Americas 0.6%; Ashkenazi 1.0%; Finnish 0.9%; Middle Eastern 0.4%; Amish 2.0%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Mean Platelet Volume. Evidence: 8/10. Source: PMID 19110211. Typical.
Platelet Count. Evidence: 8/10. Source: PMID 22139419. Slightly Higher.
Stroke
Post-Stroke Survival. Evidence: 3/10. Source: PMID 32576634. Lower Survival Rate.
Showing effects for C/T genotype
Mean Platelet Volume. Evidence: 8/10. Source: PMID 19110211. Increased.
Platelet Count. Evidence: 8/10. Source: PMID 22139419. Typical.
Post-Stroke Survival. Evidence: 3/10. Source: PMID 32576634. Higher Survival Rate.
Showing effects for T/T genotype
Mean Platelet Volume. Evidence: 8/10. Source: PMID 19110211. Highly Increased.
Platelet Count. Evidence: 8/10. Source: PMID 22139419. Slightly Lower.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
This genotype represents the most common genetic profile globally, found in over 90% of the population. Having two copies of the C allele means your platelets are of typical average size, or mean platelet volume [1]. Larger platelets are generally more reactive and prothrombotic, so having typical-sized platelets is considered a neutral baseline for cardiovascular health [2]. However, clinical research has uncovered a paradoxical relationship: stroke patients with the C/C genotype had higher one-year mortality rates compared to those carrying the T allele [3]. This suggests that while your platelets are not enlarged, they may lack certain protective properties during recovery from a vascular event [3].
Typical mean platelet volume; Slightly higher platelet count; Standard baseline cardiovascular risk.
Sample genotype: CT (Heterozygous)
Having one copy of the T allele increases your mean platelet volume, meaning your body produces larger platelets on average [1]. Larger platelets contain more active substances and tend to clump together more readily, which is a known contributor to cardiovascular risk [2]. Despite this prothrombotic tendency, clinical studies have shown that stroke patients carrying the T allele have a 70% lower risk of mortality within one year of the event [3]. This suggests a complex biological trade-off where larger platelets might play a different, potentially protective role during acute recovery [3]. Additionally, this genotype is associated with a slightly lower overall platelet count, balancing the total clotting potential [2].
Increased mean platelet volume; Slightly lower platelet count; Improved post-stroke survival rate.
Sample genotype: TT (Homozygous)
Having two copies of the T allele is associated with the largest average platelet size, or mean platelet volume [1]. Larger platelets are metabolically more active and aggregate more rapidly, which is traditionally linked to higher cardiovascular risk [2]. However, carrying the T allele is also associated with a lower risk of arterial stiffness, which may protect blood vessels [3]. Most notably, clinical research indicates that stroke patients with the T allele experience a significantly lower one-year mortality rate compared to those with the C/C genotype [3]. This suggests that the T allele confers a survival advantage during vascular recovery despite promoting larger platelets [3]. You also likely have a slightly lower overall platelet count, which helps balance overall clotting dynamics [2].
Significantly increased mean platelet volume; Lower overall platelet count; Improved post-stroke survival rate.
Variants with shared genetic architecture
rs10886430 · GRK5 Gene · Chr 10 · Blood Clot Risk
rs12041331 · PEAR1 Gene · Chr 1 · Blood Thinner Response
rs1354034 · ARHGEF3 Gene · Chr 3 · Platelet Count and Size
New gene functions in megakaryopoiesis and platelet formation.
A genome-wide association study identifies three loci associated with mean platelet volume.
Mean platelet volume and its genetic variants relate to stroke severity and 1-year mortality.
Content updated August 2026.
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