CYP2D6 rs1135839: What Your Genotype Means
The rs1135839 variant is a single nucleotide polymorphism located within the CYP2D6 gene, which encodes a critical liver enzyme responsible for metabolizing many common medications. This variant serves as a key marker in defining specific CYP2D6 star alleles, which are used to categorize how individuals may process certain drugs.
What each genotype means
Normal enzyme expression
This genotype is associated with the reference expression levels of the CYP2D6 enzyme. Because this variant is a component of common haplotypes like *2, your overall metabolic capacity depends on the full combination of your CYP2D6 alleles. Please discuss your medication response and any potential dosing adjustments with your clinician or pharmacist.
This is a common genotype found globally, though its frequency varies significantly depending on the prevalence of the *2 haplotype in your ancestral population.
Altered enzyme expression
Carrying one copy of this variant may influence the basal expression or activity of the CYP2D6 enzyme, as it is a defining marker for specific haplotypes such as *2 or *10. The clinical significance of this change depends on your other CYP2D6 genetic markers and the specific medication being metabolized. Always consult with your healthcare provider or pharmacist regarding how this may affect your personal treatment plan.
This heterozygous genotype is frequently observed across diverse global populations, reflecting the high prevalence of the associated haplotypes.
Modified enzyme expression
This genotype indicates the presence of this variant on both copies of your CYP2D6 gene, which is a core feature of certain haplotypes known to modulate enzyme activity. While this may alter how your body processes specific drugs, the overall impact is determined by your complete CYP2D6 profile. Please review your medication list and potential dosing needs with your clinician or pharmacist.
This genotype is common in many populations, particularly where the *2 or *10 haplotypes are prevalent.
Understanding the SNP and Its Location
The variant rs1135839 is a specific genetic change located within the CYP2D6 gene on chromosome 22. In the field of genomics, this gene is part of a complex cluster that includes several pseudogenes, which are non-functional DNA sequences similar to the active gene. Because of this structural complexity, identifying specific variants like rs1135839 is essential for researchers to distinguish between different functional versions of the gene. This SNP is not an isolated marker; rather, it is a component of the core haplotype—a set of DNA variations inherited together—that defines well-known CYP2D6 star alleles, such as *2 and *10. By tracking these specific combinations of SNPs, scientists can better understand the genetic architecture of the CYP2D6 locus and how it varies between individuals.
The Role of the CYP2D6 Gene
The CYP2D6 gene provides instructions for making an enzyme that is primarily expressed in the liver. This enzyme is a member of the cytochrome P450 family, which is responsible for the metabolism of a vast array of substances, including a significant portion of clinically used drugs such as antidepressants, antipsychotics, and pain medications. The activity of this enzyme can vary greatly from person to person, leading to different metabolic phenotypes: poor, intermediate, normal, or ultrarapid metabolizers. Because the CYP2D6 gene is highly polymorphic, meaning it has many different versions, an individual's specific genotype can dictate how efficiently their body breaks down or activates these medications. Understanding these variations is a cornerstone of pharmacogenomics, the study of how genes affect a person's response to drugs.
Research Associations and Evidence Strength
Research into rs1135839 primarily focuses on its role as a defining marker for CYP2D6 star alleles. While the variant itself is well-documented in databases like dbSNP, its individual clinical impact is often evaluated in the context of the larger haplotype it belongs to. The evidence linking this specific SNP to clinical outcomes is considered limited when viewed in isolation, as the functional impact on the enzyme is usually determined by the combination of multiple variants within the gene. Studies have explored associations between various CYP2D6 polymorphisms and drug response or disease susceptibility, but results can be mixed or controversial. It is important to note that while genetic associations are observed in population studies, they do not provide a definitive prediction of how a specific individual will respond to a medication. Always consult with a healthcare provider or pharmacist to discuss how your genetic profile might influence your treatment plan.
What You Can and Cannot Do With This Information
Knowing your genotype for rs1135839 provides insight into your genetic makeup, but it is not a diagnostic tool. You cannot use this information to self-diagnose conditions or make independent decisions about your medication dosages. Pharmacogenomic testing is a complex field where results must be interpreted by qualified clinicians who consider your entire genetic profile, medical history, and current medications. If you have received genetic testing results, the most appropriate step is to share them with your doctor or a clinical pharmacist. They can help determine if your specific CYP2D6 status warrants any adjustments to your therapy. Never stop or change the dose of a prescribed medication based on genetic data without professional medical guidance, as doing so could have serious health consequences.
How common is this variant?
The rs1135839 variant is common globally, with a minor allele frequency (MAF) typically ranging between 0.25 and 0.45 across European, Asian, and African populations.
Frequently asked questions
What is the CYP2D6 gene?
The CYP2D6 gene encodes a liver enzyme that plays a major role in metabolizing many common prescription drugs. Variations in this gene can lead to differences in how quickly or slowly a person processes these medications.
Is rs1135839 a dangerous mutation?
No, rs1135839 is a common genetic variant, not a disease-causing mutation. It is a normal part of human genetic diversity that helps define different versions of the CYP2D6 gene.
Can I use this SNP to predict my drug response?
While this SNP is a marker for CYP2D6 function, it is only one piece of a larger puzzle. Predicting drug response requires looking at the entire gene and other factors, so you should always discuss your results with a clinician.
Where can I find more information on CYP2D6 star alleles?
The Pharmacogene Variation (PharmVar) Consortium is the primary resource for standardized nomenclature and information regarding CYP2D6 star alleles. You can visit their website to learn more about how these alleles are defined.
Sources & further reading
Educational information only, last refreshed 9/19/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Get my report — $29Related variants in CYP2D6
This variant is a key marker for the CYP2D6*10 allele, which results in reduced enzymatic activity and altered metabolism of various psychiatric and analgesic medications.
This variant defines the CYP2D6*4 non-functional allele, which causes impaired metabolism of numerous clinically prescribed medications including antidepressants, tamoxifen, and codeine.
Defines the CYP2D6*17 allele (p.Thr107Ile), which exhibits reduced enzyme activity towards substrates like codeine and certain antidepressants.
Defines the CYP2D6*29 variant (p.Val338Met) conferring decreased metabolic capacity, primarily observed in populations of African descent.
Promoter variant defining the CYP2D6*41 allele, associated with reduced enzyme expression and decreased metabolic capacity for various drugs.
Defines the non-functional CYP2D6*41 splice defect associated with intermediate metabolizer phenotype affecting codeine, tamoxifen, and SSRI metabolism.