Genetic susceptibility measures the predisposition of an individual to manifest a certain phenotype based on his or her genetic makeup. The phenotype is known as the visible expression or manifestation of the genotype (information represented in the DNA) which can be determined, to a greater or lesser extent, by the individual's environment and lifestyle. Through the analysis of the different single nucleotide polymorphisms (known as SNPs) and by applying the polygenic risk score methodology, it is possible to estimate the genetic risk that a given person has of presenting a disease or complex trait.
This is the biological discipline that studies the effect of an individual's genetic variability on his or her response to certain drugs. It offers the possibility of identifying the most effective drugs, applying the best doses and optimal concentrations of these drugs, avoiding undesirable side effects according to the genetic pattern of each individual. This will make it possible to move away from empiricism when prescribing, substantially reducing the need for hospitalization and the associated costs. When an active ingredient is administered, it is absorbed and distributed to its site of action where it interacts with its substrate (receptors and enzymes), is metabolized and then excreted. At each of these steps there could be a genetic variation with a different clinical outcome. The ultimate goal is to unravel the increasing complexity of the human genome and to understand how individual genetic variations influence drug metabolization, a challenge for the coming decades and a priority due to its important implication in clinical practice.