Genotype underlying this is possibly partly based on linkage disequilibrium of ABO gene with the DBH gene with high levels found in the spectrum of A>O>B. This would decrease the dopamine to norepinephrine ratio and thus increase Persistence trait and decrease Impulsiveness trait. Other traits found related to higher DBH and ABO A>O>B>AB include increased sensation seeking, increased attachment, high openness to warm communication, high dependence, high pain perception.
While research has been done on ABO blood groups and personality, no consensus exists. As more genomic research is done, more will be known, but some data is available on whole genomic comparison. One starting point would be to look at the difference between the genomes of two well known individuals one of whom, Craig Venter, has ABO A, and one, James Watson, has ABO O. In looking at their catecholamine genes for differences, one finds lower MAOA in the individual with ABO O genetics. This could be a factor as lower MAOA would increase catecholamine levels and thus decrease drive behaviors. And other research has supported ABO O association with low MAOA.
While assessing personality by appearance is interesting, it also has many non-transfusion related and non-obstetric related clinical uses given the increasing knowledge about how ABO genes associate with health risks. Cardiovascular and thromboembolic disease is associated with non-O blood groups. Cancers, most definitively pancreatic, is associated with non-O blood groups. Neurologic illness tends to follow that pattern as well. Mental health diagnoses are not as clearly related though some research does support that. Given the logic of mind-body connection, more will be found in future research. And given the research showing that mental health diagnoses may represent extremes of personality traits, the relevance of work on ABO blood groups and personality traits seems reasonable.
While the more genomic research is done, the more it appears that complexity of genotype-phenotype relationship is the rule instead of the exception, the consensus that most traits are at least 50% genetic makes understanding genotype-phenotype
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