Sociodemographic characteristics and genotype distribution for the proenkephalin SNPs studied in the Caucasian Greek cohort.

All subjects were healthy control males from a highly homogenous Caucasian population of army conscripts. Minor allele frequency was 0.44 (rs2576573) and 0.46 (rs2609997). Hardy-Weinberg equilibrium for the full population: χ2 = 3.2 (p = 0.07) rs2576573 and 1.8 (p = 0.18) for rs2609997. SD: standard deviation.#one non-smoker with missing genotype;##one smoker and two non-smokers with missing genotype.