Association of Genetic Variants, Such as the μ-Opioid Receptor 1 (OPRM1) rs1799971 and Catechol-O-Methyltransferase (COMT) rs4680, with Phenotypic Expression of Fibromyalgia.

Background/Objectives: Genetic variants, such as the µ-opioid receptor 1 (OPRM1) rs1799971 and the catechol-O-methyltransferase (COMT) rs4680, have been considered among the potential causes in the development of some chronic pain conditions. In this regard, there are controversial results regarding their roles in fibromyalgia (FM). We aimed to investigate whether the OPRM1 rs1799971 and COMT rs4680 polymorphisms are associated with the development of or susceptibility to FM, as well as their potential association with syndrome characteristic variables, in a sample of the Spanish population with and without FM. Methods: The present study analysed COMT Val158Met and OPRM1 Asn40Asp genetic variants in 311 FM patients (301 women and 10 men) and 135 non-FM participants (120 women and 15 men). In addition to clinical variables, widespread pain index (WPI), symptom severity scale (SSS) (fatigue, rest quality, and cognitive symptoms), pain, stress episodes, and Borg scale were collected. Results: The main results indicate that women carrying the Val/Val genotype (i.e., high COMT activity) exhibited significantly lower levels of fatigue, cognitive impairment, and total SSS than heterozygote carriers. In addition, Met allele carriers (i.e., lower COMT activity) showed higher probabilities of suffering a stress episode and higher levels of exertion during daily activities. Conclusions: The present research suggests a link between dopaminergic dysfunction and exacerbated, frequently described symptoms in female FM patients. Although further research with wider genetic variants and recruited patients is needed, these results point out the necessity of considering gender as a separate category in chronic pain studies.