Genomics and pharmacogenomics of brain disorders.

CNS disorders are the third major problem of health in developed countries, with approximately 10% of direct costs associated with a pharmacological treatment of doubtful cost-effectiveness. There is an alarming abuse of psychotropic drugs worldwide and only 20-30% of patients with CNS disorders appropriately respond to conventional drugs. The pathogenesis of most CNS disorders is the result of the interplay of genetic and epigenetic factors with environmental factors leading to post-transcriptional changes and proteomic and metabolomic dysfunctions. It is estimated that genetics accounts for 20% to 95% of variability in drug disposition and pharmacodynamics, and about 25-60% of the Western population is defective in genes responsible for drug metabolism. In the European population only 25% of subjects are pure extensive metabolizers for the trigenic cluster integrated by the CYP2D6, CYP2C19 and CYP2C9 genes. About 50% of adverse drug events in CNS disorders might be attributed to pharmacogenomic factors. The rationale for practical pharmacogenomics and personalized therapeutics based on individual genomic profiles implies the management of different types of genes and their products including (i) genes associated with the mechanism of action of psychotropic drugs (neurotransmitters, receptors, transporters), (ii) genes encoding enzymes responsible for drug metabolism (phase I, phase II reactions), (iii) disease-specific genes associated with a particular pathogenic cascade, and (iv) pleiotropic genes with multilocative effects in metabolomic networks. The incorporation of genomic medicine procedures and pharmacogenomics into clinical practice, together with educational programs for the correct use of medication, must help to optimize therapeutics in CNS disorders.