FAAH selectively influences placebo effects.

Endogenous opioid and cannabinoid systems are thought to act synergistically regulating antinociceptive and reward mechanisms. To further understand the human implications of the interaction between these two systems, we investigated the role of the common, functional missense variant Pro129Thr of the gene coding fatty acid amide hydrolase (FAAH), the major degrading enzyme of endocannabinoids, on psychophysical and neurotransmitter (dopaminergic, opioid) responses to pain and placebo-induced analgesia in humans. FAAH Pro129/Pro129 homozygotes, who constitute nearly half of the population, reported higher placebo analgesia and more positive affective states immediately and 24 h after placebo administration; no effects on pain report in the absence of placebo were observed. Pro129/Pro129 homozygotes also showed greater placebo-induced µ-opioid, but not D(2/3) dopaminergic, enhancements in neurotransmission in regions known involved in placebo effects. These results show that a common genetic variation affecting the function of the cannabinoid system is serving as a probe to demonstrate the involvement of cannabinoid and opioid transmitters on the formation of placebo effects.

Age-of-onset of menopause is associated with enhanced painful and non-painful sensitivity in fibromyalgia.

Fibromyalgia (FM) is a chronic pain condition characterized by high prevalence in women. In particular, estrogen deficit has been considered as a potentially promoting factor of FM symptoms. This study was aimed to examine the relationship between age-of-onset of menopause and pain sensitivity in FM. For this purpose, pain sensitivity was assessed in 74 FM and 32 pain-free control women. All participants were postmenopausal and underwent a detailed semi-structured clinical interview, including data about menopause transition, previous history of hysterectomy or ovariectomy, and menses time. Participants were divided into two groups depending on age-of-onset of menopause: early menopause [≤49 years] vs. late menopause [>49 years]. Pain and non-pain thresholds were assessed by using cold, heat, mechanical, and electrical stimulation. FM women showed higher overall pain sensitivity as compared with healthy subjects. FM women with early age-of-onset of menopause displayed greater pain and non-pain sensitivity than FM women with late age-of-onset of menopause, whereas no differences were observed in healthy women due to age-of-onset of menopause. These results suggest that an early transition to menopause (shortening the time of exposure to estrogens) may influence pain hypersensitivity and could be related to aggravation of FM symptoms.

Pain sensitivity in fibromyalgia is associated with catechol-O-methyltransferase (COMT) gene.

BACKGROUND: Recent evidence suggests that genetic factors might contribute to individual differences in pain sensitivity, risk for developing clinical pain conditions and efficacy of pain treatments. The purpose of the present study was to investigate the relationship of three common haplotypes of COMT gene affecting the metabolism of catecholamines on pain sensitivity in patients with fibromyalgia (FM). METHODS: One hundred and thirteen FM patients and 65 age-matched healthy volunteers participated in the study. We genotyped four single-nucleotide polymorphisms (SNPs) (rs6269, rs4633, rs4818 and rs4680 or Val158Met) and identified haplotypes previously designated as low (LPS), average (APS) and high pain sensitivity (HPS). Thermal, pressure and touch thresholds were also examined using a quantitative sensory testing protocol. RESULTS: The frequency of genetic variations associated with low COMT enzyme activity was significantly higher in FM patients than in healthy volunteers. FM patients were more sensitive to experimental pain than healthy volunteers and, in particular, FM individuals with the met/met genotype (Val158Met SNP) or the HPS-APS haplotypes showing higher sensitivity to thermal and pressure pain stimuli than patients carrying the LPS haplotype or val alleles (Val158Met SNP). No differences due to genotype or haplotypes were found on non-painful touch thresholds. CONCLUSIONS: According with previous research, our findings revealed that haplotypes of the COMT gene and genotypes of the Val158Met polymorphism play a key role on pain sensitivity in FM patients.