These new studies invite us to change some of our views on trauma and its effect on our body. We have learned that increased glucocorticoid due to traumatic stress can cause the hippocampal atrophy and resultant memory disturbance (Yehuda, 1997), but now there is an indication that smaller volume of hippocampus itself can be a vulnerable factor for developing PTSD. In other words, resilience could be provided by an ample volume and its normal function of hippocampus which allows our capacity to resist our traumatic stress.
Yehuda, R. (1997) Stress and Glucocorticoid. Science 275: 1662-1663.
A series of studies which have been getting a lot of our attention currently deals with the serotonin transporter gene and its influence on resilience. It has been recognized that regulation of serotonin makes a contribution to emotional stability and genes for 5-HTT (serotonin transporter protein) has a large influence of child’s emotional development. Caspi and his group (Caspi, et al. 2003) studied how polymorphism in the promoter region of genes for 5-HTT moderates the influences of stressful life events on depression. This polymorphism consists of short alleles and long alleles. Based on this polymorphism, their subjects are divided into three groups: those with two copies of the short allele (17%), those with one copy of the short allele (51%), and those with two copies of the long allele (31%). The result indicated that individuals with one or two copies of the short allele exhibited more depressive symptoms, diagnosable depression, and suicidality in relation to stressful life events than individuals homozygous for the long allele. This epidemiological study thus provides evidence of a gene-by-environment interaction, in which an individual’s response to environmental stress is moderated by his or her genetic makeup.
Caspi, A., et al.S (2003)Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene Science,. 301: 386 – 389.
An important point to note here is that short allele of the genes for 5HTT itself is not the genes for depression. Those who have two short alleles are more likely to get depressed in relation to stressful life events. This means that clinical studies of trauma-related disorders are now on a new stage where how to treat them is no longer the only issue. It is also important to consider how to prevent PTSD by knowing one’s genetic makeup and related level of resilience.
By the way, some of the above-mentioned studies indicated that resilience is genetically determined, but the genes themselves are not unaltered by the environment. They are subject to “epigenetic change” in the developmental process. There was a report (Weaver, et al, 2004) that high level of rat’s maternal behaviors (increased pup licking, grooming and arched-back nursing) altered the offspring epigenome at a glucocorticoid receptor gene promoter in the hippocampus. Offspring of mothers that showed high levels of these maternal behaviors were found to have differences in DNA methylation, as compared to offspring of mothers that showed low level of maternal behaviors..
Weaver, I.C.G., Cervoni, N., Champagne, F.A., D'Alessio, AC., Sharma, S., Seckl, J.R., Dymov, S., Szyf, M. & Meaney, M.J (2004) Epigenetic programming by maternal behavior behavior Nature Neuroscience 7:847 – 854.
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