CYP2C19 rs72549307 (*8 Allele): Pharmacogenomic Impact
The genetic variant rs72549307 is a rare single-nucleotide polymorphism within the CYP2C19 gene that defines the CYP2C19*8 loss-of-function allele. Carrying this non-functional variant reduces the body's capacity to metabolize key pharmaceuticals, including the antiplatelet prodrug clopidogrel and the antidepressant escitalopram. Because of its rarity in the general population, it has limited direct clinical trial representation and is classified alongside other non-functional star alleles by pharmacogenetic consortia.
What each genotype means
Normal enzyme activity
This genotype represents the most common, fully functional version of the CYP2C19 enzyme. Individuals with this profile typically metabolize medications like clopidogrel and escitalopram at expected rates. Please discuss any medication dosing or concerns with your clinician or pharmacist.
This is the most common genotype globally, found in the vast majority of the population.
Reduced enzyme activity
This genotype includes one copy of the CYP2C19*8 loss-of-function allele, which may lead to reduced enzyme activity compared to those with two functional copies. This can potentially affect how your body processes certain drugs, such as clopidogrel or escitalopram. Please consult your healthcare provider or pharmacist to determine if this impacts your specific medication therapy.
This genotype is rare, occurring in less than 1% of the general population, and is primarily identified in cohorts of European descent.
Significantly reduced enzyme activity
This genotype indicates the presence of two copies of the CYP2C19*8 loss-of-function allele, which is associated with severely impaired enzyme function. This may significantly alter the metabolism of medications that rely on this enzyme for activation or clearance. It is important to discuss this genetic finding with your clinician or pharmacist before starting or adjusting any relevant medications.
This genotype is extremely rare, with a frequency significantly lower than 0.5% globally.
What is rs72549307 and Where is It Located?
The single-nucleotide variant rs72549307 is located within the CYP2C19 gene on chromosome 10 at 10q23.33. At the molecular level, this variation represents a missense substitution known as c.358T>C, which results in the replacement of a tryptophan residue with an arginine at codon 120 (p.Trp120Arg). In pharmacogenomic nomenclature curated by the Pharmacogene Variation (PharmVar) Consortium, this specific single-nucleotide change characterizes the CYP2C19*8 allele. Structurally, the replacement of this conserved amino acid disrupts normal protein folding or catalytic integrity, resulting in a protein with absent or negligible enzymatic capability. Unlike widespread non-functional variants like CYP2C19*2 or *3, which represent splicing or premature stop mutations, *8 is an uncommon missense alteration that leads to a similar functional null phenotype.
The Role of the CYP2C19 Enzyme in Drug Metabolism
The CYP2C19 gene provides the biological instructions for synthesizing cytochrome P450 2C19, a vital membrane-bound enzyme anchored in the endoplasmic reticulum of liver hepatocytes. This enzyme acts as a catalyst in the phase I oxidative metabolism of roughly 10% of commonly prescribed therapeutic drugs. Its substrates include cardiovascular agents such as clopidogrel, selective serotonin reuptake inhibitors (SSRIs) such as escitalopram and citalopram, and proton pump inhibitors like omeprazole. The functional outcome of CYP2C19 activity depends on the drug: for prodrugs like clopidogrel, the enzyme is required to bioactivate the compound into its antiplatelet form. For active drugs like escitalopram, the enzyme plays a primary role in clearing and inactivating the compound, protecting against excessive drug accumulation.
Research Associations and Evidence Strength
Clinical consortia like the Clinical Pharmacogenetics Implementation Consortium (CPIC) and PharmGKB classify CYP2C19*8 as a definitive 'no function' allele. However, the direct clinical evidence base specifically tracking rs72549307 outcomes is categorized as limited. Because rs72549307 is rare, broad-scale randomized cardiovascular and psychiatric trials evaluate outcomes by pooling it into aggregate 'loss-of-function' (LOF) or 'poor metabolizer' cohorts alongside common alleles like *2. In carriers of two loss-of-function alleles, clopidogrel bioactivation is severely diminished, leading to reduced platelet inhibition and elevated risks of secondary ischemic events. Conversely, for escitalopram, reduced clearance elevates plasma drug concentrations, increasing the likelihood of adverse side effects. While the mechanistic null assignment is experimentally sound, variant-specific statistical power in isolated studies remains modest.
Population Frequency and Ancestry Patterns
The rs72549307 variant is an exceedingly rare allele on a global scale. In major genomic repositories such as the Genome Aggregation Database (gnomAD) and PharmVar population surveys, the minor allele frequency (MAF) consistently measures below 0.005 (<0.5%). The variant has been observed predominantly in European-descent cohorts at very low frequencies and is virtually undetectable or absent in East Asian, African, and Indigenous populations. Consequently, homozygous carriers (C/C) are extraordinarily rare in clinical genetics. The vast majority of individuals carrying this variant are heterozygous (C/T), inheriting one null *8 allele paired with a normal function allele (*1) or another loss-of-function allele (*2 or *3), placing them in the intermediate or poor metabolizer phenotype classes.
Clinical Implications and How to Use This Information
Understanding your rs72549307 status offers useful insight into how your liver handles certain medications, but genetic data alone should never dictate your medical care. Never initiate, discontinue, or alter dosages of any medication—including antiplatelet agents like clopidogrel or antidepressants like escitalopram—without explicit guidance from a prescribing physician or pharmacist. Clinicians assess comprehensive clinical factors, such as kidney function, age, body weight, concurrent drug therapies, and overall cardiovascular risk, alongside your genotype. If a clinical pharmacogenetic test identifies a CYP2C19*8 allele, professional guidelines from organizations like CPIC and the FDA provide actionable recommendations to select alternative antiplatelet therapies or modify SSRI dosing to ensure safety and effectiveness.
How common is this variant?
The rs72549307 (C) allele is an extremely rare null variant with a global minor allele frequency below 0.005 (<0.5%), detected primarily in individuals of European ancestry and rarely found in other global populations.
Frequently asked questions
Does carrying rs72549307 mean clopidogrel will not work for me?
Carrying rs72549307 reduces your liver's ability to convert clopidogrel into its active antiplatelet form. If paired with another non-functional allele, clopidogrel may be significantly less effective, raising your risk for blood clots; however, only your doctor can determine if an alternative medication is necessary.
How does rs72549307 affect antidepressants like escitalopram?
The CYP2C19 enzyme is responsible for clearing escitalopram from the bloodstream. Carrying this loss-of-function variant can cause escitalopram to clear more slowly, potentially leading to higher drug concentrations and a greater risk of adverse effects, requiring careful dose monitoring by your physician.
Is CYP2C19*8 tested on standard genetic health screens?
Many routine commercial genetic screens only test for the most common CYP2C19 variants (*2, *3, and *17). Because rs72549307 is rare, it is usually only captured on comprehensive clinical pharmacogenetic panels that cover expanded star alleles (*4 through *8).
Can diet or lifestyle compensate for a CYP2C19*8 variant?
Dietary and lifestyle adjustments cannot alter your underlying genetic CYP2C19 enzyme structure. While avoiding certain enzyme inhibitors like omeprazole can prevent further metabolic slowdown, any medication adjustments must be managed directly by your medical provider.
Sources & further reading
Educational information only, last refreshed 9/8/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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The CYP2C19*2 loss-of-function splicing defect results in impaired biotransformation of prodrugs including clopidogrel and altered clearance of proton pump inhibitors and select antidepressants.
Defines the CYP2C19*17 increased function allele, conferring rapid or ultrarapid metabolism for CPIC-actionable drugs including clopidogrel, PPIs, and SSRIs.
Variant in the CYP2C19 locus associated with altered metabolism of clopidogrel and proton-pump inhibitors.
Defines the CYP2C19*8 loss-of-function variant (c.358T>C, p.Trp120Arg) which results in no enzymatic activity and impaired metabolism of CYP2C19 substrates.
Defines the non-functional CYP2C19*3 null allele resulting from a premature stop codon, leading to poor metabolism of drugs such as clopidogrel, escitalopram, and proton pump inhibitors.
Defines the CYP2C19*4 allele caused by an ATG start codon alteration that abolishes translation, resulting in reduced or absent drug metabolism capacity.