Genetic influences on the dynamics of pain and affect in fibromyalgia.

OBJECTIVE: The purpose of the present investigation was to determine if variation in the catechol-O-methyltransferase (COMT) and mu-opioid receptor (OPRM1) genes is associated with pain-related positive affective regulation in fibromyalgia (FM). DESIGN: Forty-six female patients with FM completed an electronic diary that included daily assessments of positive affect and pain. Between- and within-person analyses were conducted with multilevel modeling. MAIN OUTCOME MEASURE: Daily positive affect was the primary outcome measure. RESULTS: Analyses revealed a significant gene x experience interaction for COMT, such that individuals with met/met genotype experienced a greater decline in positive affect on days when pain was elevated than did either val/met or val/val individuals. This finding supports a role for catecholamines in positive affective reactivity to FM pain. A gene x experience interaction for OPRM1 also emerged, indicating that individuals with at least one asp allele maintained greater positive affect despite elevations in daily pain than those homozygous for the asn allele. This finding may be explained by the asp allele's role in reward processing. CONCLUSIONS: Together, the findings offer researchers ample reason to further investigate the contribution of the catecholamine and opioid systems, and their associated genomic variants, to the still poorly understood experience of FM.