CYP2C19 Intermediate Metabolizer Prevalence
Approximately 46-57% of certain populations carry the CYP2C19 intermediate metabolizer genotype, though this varies substantially by ethnicity.
Population-Specific Prevalence Data
The frequency of CYP2C19 intermediate metabolizers (IM) shows marked ethnic variation:
South Asian Populations
- British-South Asians (Bangladeshi/Pakistani): 57% carry at least one loss-of-function allele, making them intermediate or poor metabolizers 1
- Indian population: 46.67% are intermediate metabolizers (including *1/*2, *1/*3, and *2/*17 genotypes) 2
Other Populations
- Venezuelan populations: 20-38% intermediate metabolizers, with frequencies similar to Asian populations and higher than other South Americans 3
Key Genetic Variants Driving IM Phenotype
The intermediate metabolizer phenotype results from carrying one functional allele and one loss-of-function allele. The most common loss-of-function variants are:
CYP2C19*2: Most prevalent LOF allele
- South Asians: 32.5% minor allele frequency
- East Asians: 31%
- Africans: 18%
- Non-Finnish Europeans: 15%
- Latinos: 10% 4
CYP2C19*3: Less common, rare in Europeans (0.025%) and Africans (0.037%) but more prevalent in Asians 4
Clinical Significance
Intermediate metabolizers have clinically meaningful reductions in clopidogrel active metabolite levels—approximately 32% lower AUC compared to normal metabolizers 4. This translates to:
- Higher rates of high residual platelet reactivity on clopidogrel
- Increased risk of major atherothrombotic events (adjusted HR 1.51-2.22 depending on concomitant CYP2C19 inhibitor use) 5
- 3-fold increased risk of recurrent myocardial infarction in poor metabolizers 1
Important Caveats
The prevalence estimates vary based on:
- Ethnic background: South Asian and East Asian populations have the highest frequencies of IM phenotypes
- Which alleles are tested: Studies testing only *2 and *3 may underestimate IM prevalence compared to those also testing gain-of-function alleles like *17
- Phenotype classification systems: Different guidelines may classify certain genotypes (e.g., *2/*17) differently 6
Given these high frequencies, particularly in South Asian populations where over half carry reduced-function alleles, preemptive CYP2C19 genotyping before clopidogrel prescription is increasingly recommended 7.