Clarifying the Origin of Biological Abnormalities in PTSD Through the Study of Identical Twins Discordant for Combat Exposure

Harvard University, Cambridge, Massachusetts, United States
Annals of the New York Academy of Sciences (Impact Factor: 4.38). 08/2006; 1071(1):242-54. DOI: 10.1196/annals.1364.019
Source: PubMed


A biological abnormality found to be associated with posttraumatic stress disorder (PTSD) may be, among other things, a pretrauma vulnerability factor, that is, it may have been present prior to the event's occurrence and increased the individual's likelihood of developing PTSD upon traumatic exposure. Alternately, it may be an acquired PTSD sign, that is, it may have developed after the traumatic exposure, along with the PTSD. We have studied pairs of Vietnam combat veterans and their noncombat-exposed, identical twins in an effort to resolve these competing origins. Combat veterans were diagnosed as current PTSD or non-PTSD (i.e., never had). Average heart rate responses (HRRs) to a series of sudden, loud-tone presentations were larger in Vietnam combat veteran twins with PTSD, but these larger responses were not shared by their noncombat-exposed cotwins, whose responses were similar to those of the non-PTSD combat veterans and their noncombat-exposed cotwins. These results suggest that larger HRRs to sudden, loud tones represent an acquired sign of PTSD. In contrast, increased neurological soft signs (NSSs), diminished hippocampal volume, and presence of abnormal cavum septum pellucidum (CSP) were found in Vietnam combat veteran twins with PTSD and their "high-risk," unexposed cotwins compared to Vietnam combat veteran twins without PTSD and their "low-risk," unexposed cotwins. These results support the conclusion that the latter abnormalities represent antecedent, familial vulnerability factors for developing chronic PTSD upon exposure to a traumatic event.

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    • "Several potential PTSD biomarkers including disturbances in hormones or neurotransmitter systems, impaired physiological responses to stimuli, and structural or functional brain abnormalities have been investigated (Lanius et al., 2002; Yehuda et al., 2002; Karl et al., 2006; Pitman et al., 2006; Geuze et al., 2008; Kovacic et al., 2008; Eckart et al., 2011; Zolad and Diamond, 2013); yet, none have previously emerged as definitive PTSD biomarkers. Indeed, to be useful, a PTSD biomarker must first be both reproducible and highly accurate; many previously proposed biomarkers meet one but not both of these criteria. "
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    • "A recent meta-analysis further supported the hypothesis that impairments in cognitive functioning, in this case verbal memory, are partially related to illness duration (). It is important to note, however, that questions remain if these biological abnormalities are an acquired PTSD sign or pretrauma vulnerability factors that increase likelihood of developing PTSD after trauma exposure (Pitman et al., 2006). Another possibility some may argue for the findings in the current study is that the PTSD-fail group reported significantly more symptoms on the PCL than the other groups, thus explaining why they performed significantly poorer on all measures of neuropsychological functioning. "
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