Genetic vulnerability refers to the inherited characteristics passed on from parents to children that make it more likely that a person will develop an addiction. For example, research by Slutske et al. (2010) found that identical twins had a higher concordance rate for pathological gambling (49% for male pairs and 55% for female pairs) in comparison to non-identical twins (21% for male pairs and for female pairs). In terms of specific genes, Blum and Payne (1991) correlated the dopamine D2 Receptor Taq 1 allele with alcoholism. This gene is associated with decreased dopamine availability in the reward centre of the brain, which means that anything which increases dopamine levels will produce strong feelings of pleasure. Blum called this gene a ‘reward gene’ and it is also related to other addictive behaviours, including drug addiction, smoking, overeating, and pathological gambling.