Association of functional variations in COMT and GCH1 genes with postherniotomy pain and related impairment

Persistent postoperative pain is a well-established clinical problem with potential severe personal and socioeconomic implications. The prevalence of persistent pain varies across surgery types. Severe persistent pain and related impairment occur in 5% to 10% of patients after groin hernia repair. The substantial interindividual variability in pain-related phenotypes within each surgery type cannot be explained by environmental factors alone, suggesting that genetic variation may play a role. We investigated the contribution of COMT and GCH1 to persistent postherniotomy pain (PPP)-related functional impairment. Prospective data from 429 Caucasian male patients with hernia were collected. Three COMT and 2 GCH1 tagging single-nucleotide polymorphisms (SNPs) were genotyped and analyzed for association with PPP-related activity impairment at 6 months after herniotomy. Fifty-five (12.8%) patients had moderate-to-severe pain-related activity impairment 6 months postoperatively as measured by Activity Assessment Scale (≥8.3). Patients with the G allele of COMT SNP rs6269 and C allele of COMT SNP rs4633 had less impairment (P = 0.03 and 0.01, respectively); in addition, the COMT haplotype GCG was associated with less impairment. For GCH1, the A allele of SNP rs3783641, T allele of rs8007267, and AT haplotype showed a protective effect trend (although nonsignificant; P = 0.08, 0.06, and 0.08, respectively). A prediction model of substantial PPP-related activity impairment, combining COMT and GCH1 SNPs with clinical, psychophysical, and psychological risk factors, had a "good" (0.8 < area under curve < 0.9) discriminatory power. These data suggest that functional variations in COMT and GCH1 combined with clinical factors are predictive of PPP-related impairment after groin herniotomy.