This glossary provides clear definitions of the key terms and concepts driving the CERSI-PGx project. As pharmacogenomics moves into routine clinical practice, establishing a shared technical language is essential for effective collaboration across research, regulation, and healthcare delivery. These definitions support the interpretation of our clinical guidelines and work package findings.

Pharmacogenomics (PGx): the study of how an individual’s genetic makeup (genome) influences their response to medications. Studies the influence of the entire genome and how multiple genes and their interactions affect drug response.

Pharmacogenetics: the study of variability in drug response due to heredity. Focuses on individual genes and their variations (e.g., single nucleotide polymorphisms or SNPs).

Chromosome: genetic structures that usually occur in functional pairs in the nucleus of cells (except in gametes and bacteria).

Gene: a short length of DNA found on a chromosome that codes for a particular characteristic or protein.

Genomics: the study of the entire genome of an organism.

DNA Sequencing: the process of determining the precise order of the four nucleotide bases (adenine, guanine, cytosine, and thymine) that make up a DNA molecule.

Genetic variation: the presence of differences in DNA sequences between individuals within a population.

Germline variants: A variant that occurs in a gamete (egg or sperm) or cells that produce gametes (germ cells). The resulting embryo and baby will have the variant in every cell of their body that contains a copy of the genome, including the cells that produce their own gametes. 

Somatic variants: Cells that are not part of the germline are called somatic cells, and any changes to the DNA that occur within these cells are known as somatic variants. They are not present in every cell in the body, and are not passed from parent to child. A somatic variant can be present in a large number of cells in the body or just a few, depending on when in a person’s lifetime the new variant occurs.

Allele: Each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Haplotype: a set of genetic determinants located on a single chromosome.

Adverse drug reaction (ADR): An unintended response to a medicine that occurs during normal use.

Drug-drug interactions (DDI): occur when one drug’s effect is altered by another drug, food, supplement, or even a medical condition, which can increase toxicity or decrease efficacy.

Toxicity: the harmful effect that occurs when the concentration of a drug in the bloodstream or tissues exceeds a safe level, whether due to overdose, impaired metabolism, or an adverse reaction to a normal dose.

Efficacy: the capacity of a medication (or other intervention) to produce a beneficial change or therapeutic effect under ideal, controlled conditions.

Pharmacokinetics (PK): describes the concentration–time course of a drug in plasma after dosing.

Pharmacodynamics (PD): links plasma drug concentration to the observed effect intensity (desired or undesired).

Pharmacovigilance (PV): the science and activities of detecting, assessing, understanding, and preventing the side effects of medicines. This continuous process monitors drugs from clinical trials through their marketing and patient use to identify and evaluate adverse drug reactions, with the ultimate goal of ensuring and improving patient safety.

Companion diagnostic: a medical device, often an in vitro diagnostic (IVD), which provides information that is essential for the safe and effective use of a corresponding drug or biological product.

Medical device: any instrument, apparatus, appliance, software, implant, or material intended for medical purposes, such as diagnosing, monitoring, treating, or preventing disease. 

Phenotype: the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Polypharmacy: the use of multiple medicines by one individual.

Polymorphisms: the presence of genetic variation within a population, upon which natural selection can operate.

Single nucleotide polymorphism (SNP): a variation in a single DNA building block (nucleotide) that occurs at a specific position in the genome.