title: Physiologic responses to sudden, loud tones in monozygotic twins discordant for combat exposure: association with posttraumatic stress disorder.
abstract: BACKGROUND
  Larger heart rate responses to sudden, loud (startling) tones represent one of the best-replicated psychophysiologic markers for posttraumatic stress disorder (PTSD). This abnormality may be a pretrauma vulnerability factor, ie, it may have been present prior to the event's occurrence and increased the individual's likelihood of developing PTSD on traumatic exposure. Alternately, it may be an acquired PTSD sign, ie, it may have developed after the traumatic exposure, along with the PTSD. Studying identical twins discordant for traumatic exposure offers an opportunity to resolve these competing origins.
  
  
  METHODS
  Subjects included pairs of Vietnam combat veterans and their non-combat-exposed, monozygotic twins. Combat veterans were diagnosed as having current PTSD (n = 50) or non-PTSD (ie, never had) (n = 53). All subjects listened to a series of 15 sudden, loud tone presentations while heart rate, skin conductance, and orbicularis oculi electromyogram responses were measured.
  
  
  RESULTS
  Consistent with previous reports, averaged heart rate responses to the tones were larger in Vietnam combat veterans with PTSD. These larger responses were not shared by their non-combat-exposed co-twins, whose responses were similar to those of the non-PTSD combat veterans and their non-combat-exposed co-twins. This result remained significant after adjusting for a number of potentially confounding factors.
  
  
  CONCLUSIONS
  The results suggest that larger heart rate responses to sudden, loud tones represent an acquired sign of PTSD rather than a familial vulnerability factor.
authors.affiliation: Department of Psychiatry, Massachusetts General Hospital and Harvard Medical School, Boston, USA. scott_orr@hms.harvard.edu
authors.forename: Scott P
authors.initials: SP
authors.lastname: Orr
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Metzger
authors.forename: Natasha B
authors.initials: NB
authors.lastname: Lasko
authors.forename: Michael L
authors.initials: ML
authors.lastname: Macklin
authors.forename: Frank B
authors.initials: FB
authors.lastname: Hu
authors.forename: Arieh Y
authors.initials: AY
authors.lastname: Shalev
authors.forename: Roger K
authors.initials: RK
authors.lastname: Pitman
mesh_terms: D000161:Acoustic Stimulation; D001767:Blinking / Q000502:physiology; D003130:Combat Disorders / Q000175:diagnosis* / Q000503:physiopathology / Q000523:psychology; D004200:Diseases in Twins / Q000175:diagnosis*; D004576:Electromyography; D005712:Galvanic Skin Response / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D013216:Reflex, Startle / Q000502:physiology*; D012042:Registries; D012107:Research Design; D013313:Stress Disorders, Post-Traumatic / Q000175:diagnosis* / Q000503:physiopathology / Q000523:psychology; D014430:Twins, Monozygotic; D014728:Veterans / Q000523:psychology; D014744:Vietnam