GCH1 and Pain Sensitivity 15 single nucleotide polymorphisms 15 single nucleotide polymorphisms Pain protective haplotype in 15.4% Pain protective haplotype in 15.4% Distribution follows Hardy-Weinberg Equilibrium in general population Distribution follows Hardy-Weinberg Equilibrium in general population Associated with less pain following lumbar discectomy Associated with less pain following lumbar discectomy Homozygotes reduced experimental pain sensitivity Homozygotes reduced experimental pain sensitivity [Tegeder et al, Nature Med 2006] [Kim & Dionne, Mol Pain 2008]