A review of the role of genetic testing in pain medicine

Pain clinicians have always been challenged by the variability of response to pain treatment. Differences in the degree of pain stimulation and pain sensitivity, weight and age differences, prior opioid use and tolerance, as well as the differences in bioavailability of various opioid formulations have been cited as causes for the wide variability in analgesia seen with opioids. Genetics may explain the variability of responses and help to predict more effective (or less dangerous) medication choices and doses. Genetics may also help to predict the response to specific opioids and antidepressants. In this review article, we discuss the genetic influence of nociception, analgesia, and hyoanalgesia. The CYP450 enzymes involved in the metabolism and activity of opioids and adjuvant analgesics are genetically controlled, as are the opioid receptors and a variety of brain chemistries. This article discusses the specific pain implications of genetic variations in CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, CYP3A7, OPRM1, OPRK1, OPRD1, COMT, GABA, UGT, MC1R, GCH1, ABCB1, P-glycoprotein, 5HTR1A, 5HTR2A, MTHFR, CACNA2D2, and 5-HTTLPR. Recent research findings suggest the relationship between genetic predisposition and clinical behavior, including the risk of opioid misuse and addiction. While urine drug testing may hint at genetic issues regarding opioid metabolism, cheek swab DNA testing has become economically viable, and we review the current and future genetic pain issues that may influence the decisions that pain clinicians make every day. Genetic testing may explain and predict many of the clinical responses seen with opioids and adjuvant medications, and may help the clinician identify those patients at genetic risk of opioid misuse and addiction.