“The DRD4 gene has variations called alleles that differ in the number of times a segment of the gene repeats itself. The most common versions are either the 4-repeat allele, which is carried by approximately three-quarters of the population, or the 7-repeat (or more) allele. The presence of the higher-repeating alleles (7 or more) has been shown to be related to reduced sensitivity to dopamine. A reduced sensitivity to dopamine requires relatively more stimulation to provoke the same internal reward. People with at least one allele of 7-repeats or longer are more likely to engage in novelty-seeking or compulsive gambling.”