Association between a functional polymorphism on the dopamine-β-hydroxylase gene and reward dependence in two independent samples

Although the general RD-NA hypothesis was corroborated, the directionality of the observed effect was antithetical. Based on previous functionality studies reporting low enzymatic activity related to the TT genotype, present results indicate high NA levels in subjects scoring high on RD (in contrast to Cloninger's thesis). Future studies have to analyze how DBH activity and NA levels are dependent on the availability of dopamine.