2c
Kerry L. Jang and Fiona Choi
Our chapter focused on issues surrounding the search for the genes underlying personality disorder, and the excellent commentaries provided further depth of thought to move this search forward. We believe together these three pieces provide a useful summary of where the field is going. In our rejoinder, we would like to take a different approach and raise the uncomfortable question of whether where we are going is where we should be going.
Turkheimer, Petterson, and Horn (2014) wrote a very interesting paper that turned our understanding of genetics upside down. They contend that the null hypothesis (H0) geneticists have been working from is not the correct one. Our work is predicated that H0 = 0, that is, genetic influences do not exist; and that the alternative hypothesis (H1) is that genetic effects do exist and are significantly greater than zero. However, they suggest that the null hypothesis that we should be trying to reject is that genetic effects do exist (H0 > 0) and that the alternative (H1 = 0) is what we should be trying to find support for. This reversal of what H0 and H1 are has significant implications for the approach we take.
If we assume that genetic effects are an inexorable part of personality function (H0 > 0) we have to think about what genes do. Typically, genes have been thought of in terms of liability – a risk factor – for the development of personality disorder. Our job has been to find these genes and develop ways to mitigate their expression using biochemical methods or identifying triggers, such as exposures to specific environments and experiences that would turn the liability on or off. Under the new null hypothesis (H0 > 0) genetic influences are seen less as a liability, but instead as the fundamental building blocks to normal personality. As such, they confer protective factors against the influences of the environmental stressors. Genetic influences are not a liability but a reflection of the stability of consistent and characteristic behavior – the very definition of personality – and as the bulwarks against the ever changing landscape of environmental and experiential influences that bombard and impinge upon us every day.
It is when the environmental influences overwhelm genetic bulwarks that disorders develop and are maintained. From this perspective, the research focus thus shifts to the environment and identifying those aspects that are instrumental in the development of personality disorder. To date, environmental research has typically focused on models of gene–environment moderation/interaction and correlation (e.g., Carpenter, Tomko, Trull, & Boomsma, 2013; Jafee & Price, 2007) that attempt to identify environmental factors that activate liability genes. The most recent papers also focus on the notion of a genetic liability that is turned off and on by exposure (Bulbena-Cabre, Bassir Nia, & Perez-Rodriguez, 2018; Gescher et al., 2018). The point is that perhaps there are no liability genes – personality disorder genes are rather protective factors and personality disorder is when these genetic defenses are overwhelmed by environmental stressors. Perhaps some of our research focus might be productively directed at understanding what these factors are. Are these overwhelming influences a response to specific traumatic events? Perhaps they develop because of small cumulative events such as parenting practices that exist over time? Are personality disorders the result of a lifetime of observational activity as to what works and what does not? The nature of human experience and how maladaptive behaviors are maintained and supported deserve a second examination and it may mean a return to reconsider foundational ideas about personality such as those discussed by Gordon Allport or Sigmund Freud. Speaking of Gordon Allport (1937), he wrote that personality is something and personality does something. Returning to his famous dictum in the light of our failure to find any genes for personality disorder suggests that the biological basis of personality as reflected in the genes protects us from the vagaries of the environment and is not a liability at all. The inability to find liability genes just might be the most important contribution of genetics research in this field.
References
Allport, G. (1937). Personality: A Psychological Interpretation. New York: Holt, Rinehart & Winston.
Bulbena-Cabre, A., Bassir Nia, A., & Perez-Rodriguez, M. M. (2018). Current knowledge on gene–environment interactions in personality disorders: An update. Current Psychiatry Reports, 20, 74.
Carpenter, R. W., Tomko, R. L., Trull, T. J., & Boomsma, D. I. (2013). Gene–environment studies and borderline personality disorder: A review. Current Psychiatry Reports, 15, 336.
Gescher, D. M., Kahl, K. G., Hillemacher, T., Frieling, H., Kuhn J., & Frodl, T. (2018). Epigenetics in personality disorders: Today’s insights. Frontiers in Psychiatry, 9, 579.
Jaffee, S. R., & Price, T. S. (2007). Gene–environment correlations: A review of the evidence and implications for prevention of mental illness. Molecular Psychiatry, 12, 432–442.
Turkheimer, E., Pettersson, E., & Horn, E. A. (2014). Phenotypic null hypothesis for the genetics of personality. Annual Review of Psychology, 65, 515–540.