Although personality is thought to be 50% heritable, consensus has not been reached about the specific genes involved, interest in genes affecting personality and behavior continues because of the linkage of personality traits with both physical and mental illness. One hundred and twenty years of study of the ABO blood types and the genes causing them has led to more precise assignment of genotype-phenotype linkage.

Countries like Japan and Korea with 100 years history of study of ABO blood groups and personality as well as other countries have published research with no consensus.

Introversion is a well-studied personality trait with 50% genetic causation. Dopamine system has been linked to the introversion-extroversion spectrum with high dopamine linked to introversion. Dopamine beta hydroxylase determines the ratio of dopamine to norepinephrine. Dopamine beta hydroxylase gene, DBH, is in linkage disequilibrium with ABO gene thus offering insight into the ABO findings related to personality traits. ABO blood groups have been studied with some but not all studies finding type AB associated with introversion. One explanation for the inconsistent replication of findings could be that genotypes would show more differences than phenotypes. ABO A allele, ABO B allele or the synergism of both alleles could be the driver of introversion trait in ABO AB.

Patients in an obstetric gynecology practice appeared to demonstrate a tendancy to introversion in phenotype ABO B. Since we had access to ABO blood phenotypes instead of genotypes of our obstetric gynecology office patients, we hypothesized that phenotype ABO AB when compared with ABO O would be associated with higher introversion since these phenotypes were also genotypes and since ABO O unlike ABO AB is not found associated with introversion in extant research. Though ABO B allele was observed to be the likely cause of introversion in patients and since we had available only phenotypes of ABO to use in search of genetic allele that causes introversion trait, ABO AB needs to be dissected to see whether ABO A allele or ABO B allele is the driver of the introspective trait. Based on the literature and on observation, the hypothesis was that ABO B is the driver of introversion trait.

A pilot student of 225 obstetric gynecology patients using the online NPA personality test showed higher scores for introversion tendancies in ABO AB compared to ABO O and when ABO AB was compared to ABO A.

This supports ABO B as the driver of introversion tendancies in the ABO gene. Studies using ABO genotypes instead of ABO phenotypes should provide further support for this hypothesis. Given the support for introversion tendancies in personality caused by higher dopamine genetically with dopamine beta hydroxylase low activity and this dopamine state being common mechanism for such conditions as schizophrenia and autism, continued discoveries of genes that impact this state will lead to many health implications.

尽管认为人格可遗传50％，但尚未就所涉及的特定基因达成共识，但由于人格特质与身心疾病的联系，人们对影响人格和行为的基因的兴趣仍在继续。对ABO血型及其致病基因的一百二十年研究已经导致基因型-表型连锁的更精确分配。

日本和韩国等拥有100年ABO血型和性格研究历史的国家以及其他国家尚未发表研究。

内向是一种经过充分研究的人格特质，具有50％的遗传因果关系。多巴胺系统已与内向-外向谱联系在一起，而高多巴胺与内向有关。多巴胺β羟化酶决定了多巴胺与去甲肾上腺素的比例。多巴胺β羟化酶基因DBH与ABO基因连锁不平衡，从而提供了与人格特质相关的ABO发现的见解。已经对ABO血型进行了研究，但并非所有研究都发现与内向性相关的AB型。对于发现的重复复制的一种解释可能是，基因型比表型显示出更多的差异。ABO A等位基因，ABO B等位基因或两个等位基因的协同作用可能是ABO AB内向性状的驱动因素。

妇产科实践中的患者似乎表现出内向型ABO B倾向。由于我们能够获得ABO血液表型而不是我们妇产科办公室患者的基因型，因此我们假设与ABO O相比，ABO AB表型会相关内向性较高，​​因为这些表型也是基因型，并且在现有研究中未发现与ABO AB不同的ABO O与内向性相关。尽管观察到ABO B等位基因可能是患者内向性的原因，并且由于我们只有ABO表型可用于寻找引起内向性状的遗传等位基因，所以需要解剖ABO AB以查看是否是ABO A等位基因还是ABO B等位基因是内省性状的驱动力。根据文献和观察，

使用在线NPA人格测验的225名妇产科患者的试验学生显示，与ABO O相比，ABO AB的内向性倾向得分更高；当ABO AB与ABO A进行比较时，内向性倾向得分更高。

这支持了ABO B作为ABO基因内向倾向的驱动力。使用ABO基因型代替ABO表型的研究应为该假设提供进一步的支持。鉴于多巴胺在基因上具有较高的活性，而多巴胺β羟化酶的活性较低，导致人格的内向倾向得到支持，并且这种多巴胺状态是精神分裂症和自闭症等疾病的常见机制，继续发现影响这种状态的基因将导致许多健康问题。