In posttraumatic stress disorder (PTSD), intrusive thoughts, changes in mood, and other symptoms after exposure to trauma can greatly impact a person's quality of life. About 6 percent of people who experience trauma develop the disorder, but scientists don't yet understand the neurobiology underlying PTSD. Now, a new genetic study of more than 1.2 million people has pinpointed 95 loci, or locations in the genome, that are associated with risk of developing PTSD, including 80 that had not been previously identified.