Two Studies: The dopamine beta-hydroxylase (DBH) gene may be in linkage with the ABO gene

Shoko Tsuchimine, Junji Saruwatari, Ayako Kaneda, Norio Yasui-Furukori (2015), ABO Blood Type and Personality Traits in Healthy Japanese Subjects
[http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126983]

Donna K. Hobgood (2011), Personality traits of aggression-submissiveness and perfectionism associate with ABO blood groups through catecholamine activities.Medical Hypotheses, Volume 77, Issue 2, Pages 294-300.
[http://www.sciencedirect.com/science/article/pii/S0306987711002106]