Genetics · BEGINNER LESSON
Allele
An allele is a version of a gene region, often a single genetic variant or a defined combination of variants called a haplotype. In some pharmacogenetics sources, star alleles are used to name these versions.
What an allele is
An allele is a version of a gene region. In the source framework, this can mean one genetic variant or a defined combination of variants within a gene region, often called a haplotype and sometimes labeled with a star allele name. Pharmacogenetic tests may report a genotype or a diplotype; here, genotype is sometimes used broadly for both.
[1] The Clinical Pharmacogenetics Implementation Consortium's ... [2] The Clinical Pharmacogenetics Implementation Consortium’s Consensus-Based Framework for Assigning Allele Function
What is measured and why it matters
For pharmacogenes, alleles are measured by their clinical functional status: increased, normal, decreased, no, unknown, or uncertain function. These labels describe how much activity a gene product is expected to have, especially for enzymes or transporters that affect drug handling. When both alleles for a gene are known, their combination helps predict phenotype, such as normal metabolizer or poor metabolizer.
[1] The Clinical Pharmacogenetics Implementation Consortium's ... [2] The Clinical Pharmacogenetics Implementation Consortium’s Consensus-Based Framework for Assigning Allele Function
How allele function is assigned
Function is assigned from the totality of evidence, not from one result alone. The sources describe a tiered review that relies mainly on published peer-reviewed literature, with possible use of other databases to gather relevant studies. Evidence can include case reports, lab-based studies, and computational predictions, and expert review is required to judge whether the evidence is enough for a clinical function label.
[1] The Clinical Pharmacogenetics Implementation Consortium's ... [2] The Clinical Pharmacogenetics Implementation Consortium’s Consensus-Based Framework for Assigning Allele Function
Why some alleles are called no function
Some variants are often assigned no function when they are expected to stop protein production or prevent correct gene expression. Examples given include a premature stop codon, disruption of a canonical splice site, loss of the translation initiation codon, frameshift changes, or a complete gene deletion. When both alleles have no function, the phenotype can be poor metabolizer, meaning very low or no metabolic activity.
[1] The Clinical Pharmacogenetics Implementation Consortium's ... [2] The Clinical Pharmacogenetics Implementation Consortium’s Consensus-Based Framework for Assigning Allele Function
Limits of the system
Not all genes fit this framework, and alleles with unknown or uncertain function are not considered actionable. The sources also note that assigning function is resource intensive and depends heavily on expert interpretation. In addition, a genotype made of two uncertain-function or unknown-function alleles leads to an indeterminate phenotype, which does not correspond to prescribing recommendations.
[1] The Clinical Pharmacogenetics Implementation Consortium's ... [2] The Clinical Pharmacogenetics Implementation Consortium’s Consensus-Based Framework for Assigning Allele Function
SEE THE IDEA
How allele naming connects to function
A defined stretch of DNA that can contain one or more variants.
A single variant or a defined combination of variants in that region.
Assigned from evidence as increased, normal, decreased, no, unknown, or uncertain.
The predicted result, such as normal metabolizer or poor metabolizer.
A gene region can have different alleles; evidence-based function labels for those alleles are combined to predict phenotype.
Allele names describe DNA versions, and function labels translate those versions into expected biological effects.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.