Pharmacogenetics blends important components of the disciplines of genetics and pharmacology, and aims to describe the influence of inheritance on variable drug response. The field of pharmacogenetics began with a focus on drug metabolism, but it has been extended to encompass the full spectrum of drug disposition, including a growing list of transporters that influence drug absorption, distribution, and excretion as well as drug receptors. There are now numerous examples of associations between drug target polymorphisms and drug effects, which are crucial for clinical practice. Important example is the intolerance to azathioprine and 6-marcaptopurine due to thiopurine methyltransferase (TPMT) deficiency, determined by inheritance of TPMT mutated allele. Extreme intolerance to the drugs involves severe and even fatal cases of bone marrow aplasia. Another example of clinically relevant drug metabolizing enzymes’ polymorphisms affect CYP2D6, CYP2C9 and CYP2C19. Polymorphic forms of the allele modify response to antidepressant drugs and opioids (CYP2D6), warfarin (CYP2C9) and efficacy of Helicobacter pylori eradication (CYP2C19 is implicated in omeprazole metabolism). Genetically determined structure of receptors or other drug targets can also modify drug response. The best studied examples involve β₂-adrenergic receptors (treatment of asthma with β₂-adrenomimetics), dopamine receptors (neuroleptics) or ion channels (associated with long QT syndrome). Altered function of drug transporters, mediating drug absorption, distribution and elimination may be also important predictors of drug response, i.e. polymorphism of P-glycoprotein (encoded by MDR1 gene) involved in transport of immunosuppressants, anticancer drugs, glucocorticoids, protease inhibitors, statins as well as serotonin transporters (antidepressants). Based on the current knowledge it seems reasonably to state that pharmacogenetics has the potential to significantly enhance the ability of clinicians to use medications in a safe and effective manner, as such, represents an exciting field with tremendous clinical potential.

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1. C677T and A1298C MTHFR polymorphisms affect arechin treatment outcome in rheumatoid arthritis