What you carry at this position in your DNA and what research says about it.
Blood Cell Production: 10/10 evidence, 23 publications.
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Sample genotype (not yours): T/T
Typical Blood Cell and Platelet Levels
Baseline platelet and white blood cell counts are typical and remain well within normal physiological ranges. This genotype is associated with slightly lower platelet counts compared to C allele carriers.
What this genotype means: Typical baseline platelet count; Typical white blood cell levels.
Sample genotype (not yours): C/C
Platelet and white blood cell counts are slightly higher than average but remain entirely within normal physiological ranges. This genotype represents the upper end of typical baseline blood cell production.
Sample genotype (not yours): T/C
Slightly higher platelet and white blood cell counts are typical, falling comfortably within normal physiological limits. This intermediate pattern reflects balanced regulatory signaling.
Gene function and biological role
Gene Function: JAK2 encodes Janus kinase 2, a non-receptor tyrosine kinase essential for cytokine receptor signaling. It plays a pivotal role in directing the growth and division of blood cells, particularly megakaryocytes which mature into platelets. RCL1, located nearby, encodes an RNA terminal phosphate cyclase-like protein involved in ribosomal RNA processing. Physical interactions between the chromosomal region of this variant and the JAK2 promoter suggest a regulatory role in hematopoiesis. Variations in this genomic neighborhood influence how efficiently the body produces platelets and other myeloid cells.
Variant Impact: Located in an intergenic region on chromosome 9, rs385893 acts as a regulatory expression quantitative trait locus. It sits within a region of open chromatin that physically loops to interact with the JAK2 gene promoter. This structural interaction modulates the transcription of JAK2, thereby influencing megakaryocyte maturation and the downstream release of platelets into circulation. The C allele is consistently associated with higher baseline levels of platelets, neutrophils, and overall white blood cells across diverse global populations.
Key Insight: This variant physically loops across the chromosome to interact with the JAK2 gene, a master regulator of blood cell production.
Location: RCL1. Chromosome 9 · 9p24.1 · 4.8 Mb
Estimated prevalence by population
Global 32.5%; European 23.8%; African 52.7%; East Asian 4.4%; South Asian 24.6%; Americas 30.4%; Ashkenazi 35.0%; Finnish 26.8%; Middle Eastern 46.7%; Amish 37.2%.
Estimated TT genotype frequency.
Global 46.4%; European 50.0%; African 39.8%; East Asian 33.2%; South Asian 50.0%; Americas 49.5%; Ashkenazi 48.3%; Finnish 49.9%; Middle Eastern 43.3%; Amish 47.6%.
Estimated TC genotype frequency.
Global 21.1%; European 26.2%; African 7.5%; East Asian 62.4%; South Asian 25.4%; Americas 20.1%; Ashkenazi 16.7%; Finnish 23.3%; Middle Eastern 10.0%; Amish 15.2%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Platelet Count. Evidence: 10/10. Source: PMID 19820697. Typical.
White Blood Cell Count. Evidence: 10/10. Source: PMID 34594039. Typical.
Neutrophil Count. Evidence: 10/10. Source: PMID 32888493. Typical.
Lifestyle, Fitness & Aging
Aging & Longevity
Mitochondrial DNA Copy Number. Evidence: 8/10. Source: PMID 33385171. Typical.
Showing effects for C/C genotype
Showing effects for T/C genotype
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Baseline blood cell production is maintained at standard physiological levels. Having two copies of the T allele is associated with a slightly lower platelet count compared to carrying the C allele, though still entirely within the normal range [1]. Large-scale genetic studies show that this variant influences the maturation of megakaryocytes, the precursor cells that shed platelets [2]. In addition to platelets, this genotype is linked to slightly lower counts of neutrophils and total white blood cells. These minor variations represent normal human diversity rather than any clinical deficiency or disease risk. The body's natural feedback loops continue to regulate blood cell counts effectively in response to physiological demands.
Typical baseline platelet count; Typical white blood cell levels.
Sample genotype: CC (Homozygous)
Baseline platelet and white blood cell counts are positioned at the higher end of the typical range. Carrying two copies of the C allele is associated with the highest relative platelet counts for this variant [1]. This genetic influence operates by subtly enhancing the expression of JAK2, a key driver of blood cell maturation [2]. Correspondingly, neutrophil counts and overall white blood cell counts show a small, healthy increase. These variations do not constitute a medical condition and are not linked to an increased risk of thrombosis or blood disorders. The body successfully maintains proper blood viscosity and immune cell balance. This genotype simply reflects a natural genetic setting for slightly more active blood cell production.
Sample genotype: TC (Heterozygous)
Blood cell counts are maintained within typical, healthy ranges with a slight upward shift. Carrying one copy of the C allele is associated with a modest increase in platelet count compared to the T/T genotype [1]. This effect is mediated by the variant's physical interaction with the JAK2 gene, which helps govern platelet production [2]. Minor increases are also observed in neutrophil and total white blood cell counts. These subtle shifts do not elevate the risk of clotting or inflammatory disorders. Instead, they represent normal, healthy variation in how the bone marrow responds to hematopoietic signals. Overall blood cell homeostasis remains fully functional and stable.
Variants with shared genetic architecture
rs2239630 · CEBPE Gene · Chr 14 · B-Cell Leukemia Risk
rs3735485 · MYO1G Gene · Chr 7 · Immune Cell Levels
rs445 · CDK6 Gene · Chr 7 · Immune Cell Levels
Content updated August 2026.
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