Introduction Human beings differ widely in their rating and experience of painful stimulation. There are large variations in interindividual sensitivities to noxious pain, susceptibility to acute or chronic pain (even among patients with the same medical condition), and individual responses to analgesics. These individual responses arise from a multitude of factors, including environmental elements and genetic variations or polymorphisms. Understanding the factors that contribute to patient-related variability in pain behavior and responses to analgesics is critical for the effective treatment of patients and management of their pain. This chapter will review some important pain polymorphisms and how they can influence the pain behavior of patients.Genetic factors (Table 8.1) Mu opioid receptor (MOR) The mu receptor OPRM1 is the primary target site for opioid medications. The gene for this receptor is located on chromosome 6 and is a significant factor in the variability of how a patient responds to opioids. The most common single nucleotide polymorphism (SNP), or basepair change, of the MOR gene consists of a change of adenine to guanine in the 118 position that leads to a substitution of the amino acid asparagine for aspartate. This substitution affects the function of the receptor by increasing its binding affinity for β-endorphins and subsequently affects the action of opioids at the receptor site.
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