Dr. Fumiichiro Yamamoto who determined the arrangement of ABO blood-group genes says about ABO & personality.
Appendix 34 ABO & Personality
ABO Polymorphism & Personality
The idea that the ABO blood type is partially involved in the determination of personality is still quite common. This belief is especially popular in Japan and Taiwan. A series of books written by Masahiko Nomi seem to have contributed, to some degree, to the popularity of this theory. The books depicted numerous anecdotal examples, but the statistical analyses were based on subjective data rather than objective one.BUT he is not negative about the idea of ABO relation with personality.
Because of this lack of objectivity, I do not think that any association between ABO polymorphism and personality has been really demonstrated. All the claims currently made on this regard seem to be groundless. Or at least they do not seem to withstand scientific evaluation...
The following is his conclusion:
ABO gene is one of 25,000-plus genes contained in the human genome. But because of the abundance and wide distribution of ABH antigens, I will not be so surprised if in the future, the currently fashionable genome-wide association studies (GWAS) find an association between certain definable personality traits and ABO SNPs.And...
ABH antigens are expressed in the primary sensory neurons of the posterior root ganglia in the nervous system.Very interesting. (^^)