The association between pain responses and SNP rs563649 was tested in an independent cohort of healthy Caucasian subjects recruited at the University of Florida. Because of the smaller cohort size (n = 133) and necessity to control for gender in this cohort, limited genetic analyses were conducted. Only SNP rs563649 was chosen for an exploratory analysis because it exhibits the strongest individual contribution to the associations and can be considered as a marker of a functional haplotype. Analysis of covariance was used to examine the association of the rs563649 SNP with the summed z-pain scores. This analysis determined whether summed pain scores for individuals with one or two copies of minor alleles (n = 21) differed from those of individual homozygous for the major allele (n = 112), after controlling for age and gender. In agreement with association in the first cohort, the minor allele group had higher z-scores than the major allele group [0.63 (1.19) versus −0.95 (0.52)], (Supplementary Material, Table S2), although this difference did not reach statistical significance.
