The genetic predisposition or genetic susceptibility means the genetic mass able to influence in the phenotype of a person, population or species. Phenotype is known as the expression of the genotype (from DNA) dependent on the environment. It’s the visible manifestation of the genotype and it refers to any characteristic or trait of a person; it involves morphology, physiology, behavior, biochemical properties, etc. Therefore, genetic predisposition is the increase or decrease of the probability of illness depending on genetics. Through simple nucleotide polymorphisms (SNPs) and following a multiplicative mathematical model with exceptions as haplotypes, it is possible to calculate the risk that a particular person could have in developing a disease, using incidence and allele frequencies.
It is the biological discipline that studies the effect of the genetic variability of individuals in the response of said individual to certain drugs. It offers the possibility of developing a new generation of drugs, optimizing their effectiveness and safety, having therefore important implications in clinical practice. A better understanding of pharmacogenetics will facilitate personalized medicine, tailoring therapy to each patient. We would be able to identify those drugs that are more effective, the most appropriate dose and the optimum concentrations of them in blood, avoiding undesirable side effects. This new tendency will allow moving from empiricism when prescribing drugs, reducing substantially the necessity for hospitalization and its associated costs. When a drug is administered, it is absorbed and distributed to its point of action where it interacts with its substrate (receptors and enzymes); it is metabolized and then excreted. In each of these steps, a genetic variation with a different clinical outcome can exist. These inherited variations play a role in the carriage, distribution, metabolism and the interaction objectives of the different drugs. The aim is to decode the growing complexity of the human genome and to obtain this knowledge in order to understand how the individual genetic influence drug metabolism. It remains a challenge for the coming decades.