ACKR1 rs2814778: The Duffy-Null Variant and Neutrophil Counts
The rs2814778 variant in the ACKR1 gene is a genetic marker associated with the 'Duffy-null' phenotype, which leads to lower baseline neutrophil counts known as benign ethnic neutropenia (BEN). This variant is highly prevalent in populations of African ancestry and is a significant factor in the clinical assessment of patients prescribed clozapine.
What each genotype means
Duffy-null genotype
This genotype is known as the Duffy-null status because it prevents the expression of the Duffy antigen on your red blood cells. While this trait provides a protective effect against certain types of malaria, it is also associated with benign ethnic neutropenia, where you may have lower-than-average neutrophil counts that are normal for your genetic background. If you are prescribed medications like clozapine that require monitoring of neutrophil levels, please discuss your Duffy-null status with your clinician or pharmacist.
This genotype is highly prevalent in populations of African ancestry and common in those of Middle Eastern ancestry, but is rare in populations of European or East Asian ancestry.
Duffy-positive heterozygous
You carry one copy of the Duffy-null allele and one copy of the functional Duffy allele. Research indicates that individuals with this genotype typically express the Duffy antigen on their red blood cells and generally maintain neutrophil counts within standard, expected ranges. As you are Duffy-positive, you do not have the Duffy-null associated benign neutropenia profile.
The frequency of this genotype varies significantly by ancestry, appearing most often in populations with mixed ancestral backgrounds.
Duffy-positive homozygous
You carry two copies of the functional Duffy allele, meaning your red blood cells express the Duffy antigen. Your blood profile regarding neutrophil counts and Duffy antigen status is considered typical for populations where the Duffy-null variant is absent. You do not have the Duffy-null associated benign neutropenia profile.
This is the most common genotype in populations of European and East Asian ancestry, where it is found in the vast majority of individuals.
Understanding the rs2814778 Variant
The rs2814778 variant is a single nucleotide polymorphism (SNP) located in the promoter region of the ACKR1 gene, formerly known as DARC (Duffy Antigen Receptor for Chemokines). This specific genetic change involves a substitution of a thymine (T) for a cytosine (C). When an individual inherits two copies of the C allele, they exhibit the 'Duffy-null' phenotype. This means the ACKR1 protein is not expressed on the surface of their red blood cells. This variant is not a disease-causing mutation in the traditional sense; rather, it is a regulatory change that alters how the body manages certain blood cell populations. Because it is a common genetic trait in many parts of the world, it is considered a normal variation in human biology, though it has specific implications for clinical laboratory testing and medication monitoring.
The Role of the ACKR1 Gene
The ACKR1 gene encodes the Duffy antigen receptor for chemokines, a protein that acts as a receptor for various inflammatory molecules. Beyond its role in blood cell regulation, this protein serves as a gateway for the malaria parasite Plasmodium vivax to enter red blood cells. Historically, the Duffy-null phenotype provided a survival advantage in regions where malaria was endemic, as the absence of the receptor prevents the parasite from invading the cells. While this provided protection against a specific type of malaria, the absence of the receptor also influences the circulation of neutrophils—a type of white blood cell essential for immune defense. In individuals with the Duffy-null genotype, neutrophils are often sequestered in the bone marrow or other tissues, leading to lower counts in the peripheral blood, a condition clinically recognized as benign ethnic neutropenia (BEN).
Clinical Associations and Evidence
The primary clinical relevance of rs2814778 lies in the interpretation of blood tests. Because individuals with the CC genotype naturally have lower baseline neutrophil counts, they may be incorrectly flagged for neutropenia—a condition that can signal serious infection or adverse drug reactions. This is particularly critical for patients taking clozapine, an antipsychotic medication that requires strict monitoring of neutrophil levels to prevent agranulocytosis. Research indicates that patients with the Duffy-null genotype are more likely to experience lower neutrophil counts while on clozapine, which can lead to unnecessary treatment interruptions. While the association between the CC genotype and lower neutrophil counts is robust, the evidence regarding the actual risk of infection in these patients remains nuanced. Clinicians are increasingly using this genetic information to distinguish between benign, genetically-driven low counts and true drug-induced bone marrow suppression.
Population Frequency
The frequency of the rs2814778 variant varies significantly across global populations. The Duffy-null genotype (CC) is highly prevalent in populations of African ancestry, with estimates often ranging between 80% and 100%. It is also found in significant proportions of Middle Eastern populations, particularly among Bedouin Arabs and individuals with ancestry from Yemen. In contrast, the variant is extremely rare in populations of European or East Asian descent, where the majority of individuals carry the T allele and express the Duffy antigen. This stark difference in frequency highlights the importance of considering genetic ancestry when interpreting clinical laboratory results, as a 'low' neutrophil count may be a healthy, expected baseline for one individual but a clinical concern for another.
Navigating Your Genetic Information
If you are aware of your status for rs2814778, it is important to understand that this information is primarily used to provide context for blood test results. Having the CC genotype does not mean you are 'sick' or immunocompromised; it simply means your baseline neutrophil count is likely lower than the standard reference ranges established in populations where the Duffy-positive phenotype is more common. If you are prescribed medications like clozapine, share this information with your psychiatrist or pharmacist. They can use this context to interpret your blood work more accurately and ensure that your treatment plan is safe and appropriate for your specific genetic profile. Never make changes to your medication regimen based on genetic test results without consulting your healthcare provider, as they are best equipped to balance your genetic data with your overall clinical health.
How common is this variant?
The Duffy-null (CC) genotype is found in 80-100% of individuals of African ancestry and approximately 25% of those with Middle Eastern ancestry, while it is rare in European and East Asian populations.
Frequently asked questions
Is the Duffy-null genotype a disease?
No, the Duffy-null genotype is not a disease. It is a common genetic variation that results in lower baseline neutrophil counts, which is considered a normal, healthy state for many people of African and Middle Eastern descent.
Does having the CC genotype mean I have a weak immune system?
Not necessarily. While the CC genotype is associated with lower neutrophil counts in the blood, this is often described as 'benign' because it does not typically correlate with an increased risk of infection.
Why does my doctor care about this for clozapine treatment?
Clozapine requires monitoring of neutrophil counts to detect potential bone marrow suppression. Because the CC genotype naturally lowers these counts, doctors need to know your genotype to avoid misinterpreting a normal, healthy count as a sign of a dangerous drug reaction.
Can I change my genotype?
No, your genotype is determined at conception and cannot be changed. It is a permanent part of your genetic makeup.
Sources & further reading
Educational information only, last refreshed 10/27/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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The Duffy-null variant (c.-67T>C, often referenced as rs2814778) in the promoter of ACKR1 prevents expression of the Duffy antigen on erythrocytes, causing benign ethnic neutropenia (BEN) and conferring resistance to Plasmodium vivax malaria.
Provides resistance to Vivax malaria; common in those with African ancestry.