A long-term prospective evaluation of first-degree relatives of panic patients who underwent the 35% CO2 challenge

Background: This follow-up study investigated the potential priming effect of the 35% CO2 challenge on the development of anxiety disorders and/or pan ic attacks in healthy first-degree relatives of panic patients across a per iod of 3-4 years subsequent to the challenge. Methods: Thirty-one relatives who underwent the 35% CO2 challenge 3-4 years before and 14 relatives, free from psychiatric diagnoses in the same perio d were directly reevaluated for the presence of anxiety disorders and panic attacks. Results: None developed anxiety disorders and only 1, among relatives previ ously tested with the 35% CO2 challenge, reported sporadic panic attacks. Conclusions: The 35% CO2 challenge is a safe research paradigm in the inves tigation of healthy subjects with a familial vulnerability to panic, and CO 2 hypersensitivity might be considered a trait marker of an underlying fami lial vulnerability to panic disorder. Biol Psychiatry 1999;45:365-367 (C) 1 999 Society of Biological Psychiatry.