Limitations of Pharmacogenomic Testing

Consumer Genotyping Array Limitations

Consumer DNA testing services (23andMe, AncestryDNA, etc.) use genotyping arrays that test for specific known variants. These arrays do not sequence your entire genome. As a result:

• Not all known pharmacogenomic variants are covered by every array. Some clinically relevant alleles may not be detectable from your raw data.
• When a defining variant for a star allele is not on the array, we assume the reference (wild-type) allele is present. This means some alleles carrying ungenotyped variants may be missed.
• Structural variants (gene deletions, duplications, gene conversions) — particularly relevant for the CYP2D6 gene — cannot be reliably detected from genotyping array data.

Provider Compatibility

The number of pharmacogenomic markers available depends on the genotyping chip used by your DNA testing provider. Below is a summary of typical coverage expected from major providers:

Coverage levels are approximate and may change as providers update their genotyping chips. Your actual coverage is calculated during analysis and shown in your report.

Not All Genes Are Covered

DecodeMyBio analyzes a specific set of pharmacogenes with established clinical guidelines (CPIC Level A/B). Hundreds of genes may influence drug response, but only a subset have sufficient evidence for clinical actionability. Our reports reflect current guideline coverage, not the full scope of pharmacogenomic knowledge.

Phenoconversion

Your predicted metabolizer phenotype is based on your genotype alone. In practice, your actual metabolic activity can be altered by other medications you are taking. This is called phenoconversion — for example, a CYP2D6 normal metabolizer taking a strong CYP2D6 inhibitor (like fluoxetine or paroxetine) may functionally behave as a poor metabolizer.

DecodeMyBio reports do not account for phenoconversion. Your healthcare provider should consider your current medication regimen alongside your genetic results.

Polypharmacy

Drug response is influenced by the interaction between multiple medications. Pharmacogenomic reports assess gene-drug pairs individually and do not model complex drug-drug-gene interactions that occur with polypharmacy (taking multiple medications simultaneously).

Population-Specific Allele Gaps

Star allele definitions and frequency data have historically been developed primarily from populations of European descent. Individuals from underrepresented populations may carry pharmacogenomic variants that are not well-characterized or not included in current allele definition tables. This can lead to incomplete or less accurate results for some populations.

Environmental and Non-Genetic Factors

Drug response is not determined by genetics alone. Age, weight, organ function (liver, kidney), diet, smoking status, and other environmental factors significantly influence how you metabolize and respond to medications. Pharmacogenomic information is one component of a comprehensive clinical assessment.

Evolving Guidelines

Pharmacogenomics is an active area of research. CPIC and DPWG guidelines are periodically updated as new evidence emerges. A report generated today reflects current guidelines, which may change as the science evolves. Recommendations that are not actionable today may become so in the future, and vice versa.

Not a Substitute for Clinical Testing

Consumer-grade pharmacogenomic analysis from DecodeMyBio is not equivalent to clinical pharmacogenomic testing performed in a CLIA-certified laboratory. If you or your healthcare provider need validated, clinical-grade results for prescribing decisions, clinical testing should be pursued through an appropriate healthcare setting.

Despite these limitations, consumer-derived pharmacogenomic information can still offer a useful starting point for conversations with your prescriber. To understand how raw data becomes a report, read how pharmacogenomic testing works, or preview a sample Medication Safety Report.