Principles of Pharmacogenetics: Types of Genetic Variants

Single-nucleotide polymorphisms (SNPs) are the most common genetic variants, involving single-base changes in DNA. Other variants include insertions and deletions, where DNA segments are added or removed. Larger changes are called copy number variations (CNVs). These genetic variants exist at millions of positions across the human genome, contributing to individual differences in drug metabolism and response.

SNPs in noncoding regions regulate gene expression, which influences how individuals respond to medications. For example, certain SNPs can reduce platelet inhibition by clopidogrel, a common antiplatelet drug. These regulatory variants don't change protein sequences but alter the amount of protein produced, affecting drug efficacy and safety in different individuals.

Haplotypes are groups of linked SNPs inherited together as a unit on a DNA segment. They provide deeper insights into the genetic mechanisms underlying complex diseases and drug responses. By studying haplotypes rather than individual SNPs, researchers can better understand how multiple genetic variations work together to influence drug metabolism and phenotypic traits like poor metabolizer status.

Insertions add DNA segments to the genome, while deletions remove them. Smaller insertion-deletion events are termed indels. Copy number variations (CNVs) are larger changes that include gene duplications, increasing protein expression, or gene deletions, causing complete loss of function. These variations significantly impact drug metabolism and efficacy by altering the amount or activity of drug-metabolizing proteins.

Inherited nonfunctional alleles produce phenotypic traits such as poor metabolizer status, where individuals cannot efficiently metabolize certain drugs. These traits can be autosomal recessive, requiring two defective alleles, or show codominance, where heterozygotes display combined phenotypes. Understanding these inherited variations helps predict which patients will have altered drug responses and guides personalized medicine approaches.

Studying genetic variations helps predict individual drug responses and reduce adverse effects by identifying how polymorphisms in drug-metabolizing enzymes affect drug metabolism. Genetic variants influence pharmacogenetic phenotypes alterations in pharmacokinetics drug targets and biologic milieu. This knowledge enables clinicians to select appropriate medications and dosages based on a patient's genetic profile, improving treatment outcomes and safety.

Population-specific polymorphisms vary due to ancestry and evolutionary history. African Americans have the highest number of unique polymorphisms and the smallest haplotype blocks compared to other ethnic groups. These population differences in genetic variation affect how drugs are metabolized differently across populations, making it essential to study diverse groups when developing personalized medicine strategies and understanding disease susceptibility.