What you carry at this position in your DNA and what research says about it.
Duffy Blood Group and Immunity: 10/10 evidence, 42 publications.
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Sample genotype (not yours): T/T
Typical Duffy-Positive Blood Type
Normal expression of the Duffy antigen on red blood cells is present. This results in typical white blood cell counts and standard susceptibility to certain types of malaria.
What this genotype means: Standard Duffy-positive blood group; Typical white blood cell counts; Standard susceptibility to Plasmodium vivax malaria.
Sample genotype (not yours): C/C
Duffy-Negative: Malaria Protection and Lower White Blood Cells
Complete absence of the Duffy antigen on red blood cells provides resistance to certain malaria parasites. It also naturally lowers baseline white blood cell counts without increasing infection risk.
What this genotype means: Duffy-negative blood group; Harmlessly lower baseline white blood cell counts; Near-complete resistance to Plasmodium vivax malaria.
Sample genotype (not yours): T/C
Typical Duffy-Positive Carrier
Duffy antigen expression remains normal on red blood cells despite carrying one copy of the null variant. White blood cell counts and malaria susceptibility are typical.
What this genotype means: Standard Duffy-positive blood group; Typical white blood cell counts; Carrier of the Duffy-null genetic variant.
Gene function and biological role
Gene Function: The ACKR1 gene, formerly known as DARC, encodes the atypical chemokine receptor 1, which acts as the Duffy blood group antigen on red blood cells [1]. This receptor binds various inflammatory signaling molecules called chemokines and regulates their levels in the bloodstream [2]. It also serves as the primary gateway for certain malaria parasites to invade red blood cells [3]. Because of this, genetic variations in this gene have been heavily shaped by natural selection in regions where malaria is common [3].
Variant Impact: The rs2814778 variant is a single nucleotide change in the promoter region of the ACKR1 gene [1]. This change disrupts a binding site for the GATA1 transcription factor, which is essential for turning on the gene in red blood cells [1]. As a result, individuals with two copies of the variant allele do not express the Duffy antigen on their red blood cells, a state known as Duffy-negative or Duffy-null [4]. However, the gene remains normally expressed in other tissues, such as the lungs and blood vessel linings [4].
Key Insight: Two copies of the C allele completely shut down Duffy antigen expression on red blood cells, providing near-total protection against Plasmodium vivax malaria. However, this same change naturally lowers baseline white blood cell counts, which is entirely harmless but frequently misdiagnosed as a medical disorder.
Location: ACKR1. Chromosome 1 · 1q23.2 · 159.2 Mb
Origin Story: The Duffy-null variant is one of the most striking examples of recent positive selection in human history. In West Africa, where Plasmodium vivax malaria was historically endemic, the protective C allele swept through the population and is now present in nearly 100% of individuals, whereas it remains extremely rare (less than 1%) in populations of European or East Asian descent.
Estimated prevalence by population
Global 70.9%; European 99.3%; African 3.2%; East Asian 100.0%; South Asian 98.2%; Americas 82.8%; Ashkenazi 96.1%; Finnish 99.9%; Middle Eastern 67.7%; Amish 99.8%.
Estimated TT genotype frequency.
Global 10.4%; European 0.7%; African 29.3%; East Asian 0.0%; South Asian 1.8%; Americas 16.4%; Ashkenazi 3.8%; Finnish 0.1%; Middle Eastern 29.1%; Amish 0.2%.
Estimated TC genotype frequency.
Global 18.7%; European < 0.1%; African 67.6%; East Asian 0.0%; South Asian < 0.1%; Americas 0.8%; Ashkenazi < 0.1%; Finnish < 0.1%; Middle Eastern 3.1%; Amish < 0.1%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Immunity & Inflammation
Infection Susceptibility & Resistance
Malaria Resistance. Evidence: 5/10. Source: PMID 7663520. Typical Risk.
HIV Susceptibility. Evidence: 7/10. Source: PMID 18621010. Typical Risk.
Cardiovascular & Metabolic
Blood Cell & Iron Traits
White Blood Cell Count. Evidence: 10/10. Source: PMID 18179887. Typical Counts.
Pharmacogenomics
Antidepressant & Psychiatric Drug Response
Clozapine Toxicity. Evidence: 6/10. Source: PMID 30647433. Typical Risk.
Showing effects for C/C genotype
Malaria Resistance. Evidence: 5/10. Source: PMID 7663520. Highly Resistant.
HIV Susceptibility. Evidence: 7/10. Source: PMID 18621010. Increased Risk.
White Blood Cell Count. Evidence: 10/10. Source: PMID 18179887. Naturally Lower.
Clozapine Toxicity. Evidence: 6/10. Source: PMID 30647433. Increased Risk.
Showing effects for T/C genotype
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Expression of the Duffy antigen on red blood cells proceeds normally with this genotype [1]. Having this blood group means the red blood cells can be easily invaded by the Plasmodium vivax malaria parasite [2]. However, baseline white blood cell and neutrophil counts remain within the standard reference ranges [3]. There is no elevated risk of drug-induced neutropenia when taking medications like clozapine [4]. Standard clinical guidelines for blood counts apply without the need for ethnic-specific adjustments [3]. This genotype is the most common across European, Asian, and Native American populations [5].
Standard Duffy-positive blood group; Typical white blood cell counts; Standard susceptibility to Plasmodium vivax malaria.
Sample genotype: CC (Homozygous)
Absence of the Duffy antigen on red blood cells prevents the Plasmodium vivax parasite from invading, offering near-complete protection against this form of malaria [1]. This lack of expression also alters how signaling molecules interact with white blood cells, leading to naturally lower baseline neutrophil counts [2]. This benign condition, often called benign ethnic neutropenia, is entirely harmless and does not increase the risk of infections [3]. However, it can lead to false alarms on routine blood tests or unnecessary delays in chemotherapy [3]. Additionally, there is a significantly higher risk of falling below safety thresholds when taking the antipsychotic drug clozapine [4]. While some studies suggest a slight increase in HIV susceptibility upon exposure, progression of the disease is typically slower if infection occurs [5].
Duffy-negative blood group; Harmlessly lower baseline white blood cell counts; Near-complete resistance to Plasmodium vivax malaria; Increased risk of clozapine-induced neutropenia flags.
Sample genotype: TC (Heterozygous)
A single copy of the promoter variant does not significantly reduce Duffy antigen expression on red blood cells [1]. The presence of one normal allele is sufficient to allow Plasmodium vivax malaria parasites to enter red blood cells [2]. Baseline neutrophil and white blood cell levels remain within typical ranges [3]. No increased risk of clozapine-induced blood toxicity is associated with this heterozygous state [4]. Clinical blood tests can be interpreted using standard reference intervals [3]. This genotype is common in populations with admixed African ancestry [5].
Standard Duffy-positive blood group; Typical white blood cell counts; Carrier of the Duffy-null genetic variant.
Variants with shared genetic architecture
rs34599082 · ACKR1 Gene · Chr 1 · Duffy Blood Group
rs12075 · ACKR1 Gene · Chr 1 · Duffy Blood Group
rs33930165 · HBB Gene · Chr 11 · Hemoglobin C Status
Emergence of FY*A(null) in a Plasmodium vivax-endemic region of Papua New Guinea.
Ethnic and genetic causes of neutropenia: clinical and therapeutic implications.
Content updated August 2026.
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