For thermal pain, men with the G allele reported lower pain ratings, while women reported more pain [12]. Another study found the minor allele of the intronic variant rs9479757 to also be associated with a higher pressure pain threshold [13]. Although these experiments can provide valuable information about functional genetic variation, there is no guarantee that these effects are relevant to patient populations in less experimentally controlled settings. There is evidence, however, that OPRM1 variants do affect pain in some patients in a clinical setting. Women with the G allele of A118G report higher intensity pain from migraines, and have more pain and slower recovery from herniated discs [14, 15]. Fibromyalgia patients carrying the G allele also suffer from more pain, further suggesting that A118G is associated with pain sensitivity [16]. Patients with A/A genotypes have been found to have less pain from diabetic foot ulcers than G carriers [17]. Despite the evidence that the G allele of A118G is associated with increased pain from several different sources, a study of persistent widespread pain also found no association between pain ratings and genotype at A118G [18]. That study also found no association with rs563649 [18]. These findings suggest that OPRM1
