tability for impulsiveness as measured by his multidimensional personality questionnaire.

Data are accumulating at this time on the association between receptor genes and pathological gambling, for example low platelet monoamine oxidase activity and high urinary and spinal fluid levels of norepinephrine or its metabolite among pathological gamblers. There is recent evidence that pathological gamblers are more likely than others to carry the D₂A1 allele (Comings et al., 1996; Comings, 1998), which has also been linked to a spectrum of other addictive and impulsive disorders (Blum et al., 1996). The implications of these findings and their relevance are explored further.

Theoretically, specific human genes can be linked to biochemical reward and reinforcement mechanisms in the brain, which in turn can be associated with impulsive or addictive behaviors. For example, alcoholism, substance abuse, smoking, compulsive overeating, attention-deficit disorder, Tourette's syndrome, and pathological gambling may be linked in the brain by cells and signal molecules that are "hard wired" together to provide pleasure and rewards from certain behaviors. If an imbalance occurs in the chemicals that participate in this reward system, the brain may substitute craving and compulsive behavior for satiation (Blum et al., 1996). Recently, research has identified an association between the Taq A1 variant of the human dopamine D₂ receptor gene (DRD₂) and drug addiction, some forms of severe alcoholism, and other impulsive or addictive behaviors (Comings et al., 1996).

Because the impulsive and addictive disorders that are associated with this variant are also related to pathological gambling, research was conducted to determine if a similar relationship might be present with pathological gambling. Based on this premise, genetic research on pathological gambling theorizes that variants in the DRD₂ gene, and perhaps other genes, might be associated with biochemical reward and dysfunctioning reinforcement mechanisms that effectively lead pathological gamblers to behave self-destructively.