dependence in a sample of 430 unrelated ever-smokers with Fagerström Tolerance Questionnaire (61) scores of 0–2 or 7–11 (20). In addition to studies of OPRM1 variation association with nicotine withdrawal symptoms, dopamine receptor locus sequence variation has been evaluated for association with measures of nicotine withdrawal (62–63): one of two SNPs at the D2 dopamine receptor locus (DRD2) was observed to be significantly associated with acute nicotine withdrawal in interaction with time in a clinical sample of 116 smokers quitting smoking (62); and a trend towards significant association of the DRD4 Exon 3 variable number of tandem repeat polymorphism with the question “Did you feel a strong desire or craving for a cigarette?” was observed in a national probability sample of 204 current and former smokers (63).
