The gene activates the amygdala, a portion of the brain that controls its response to frightening situations, and has
     been weakly linked to increased anxiety.

     David Weinberger, chief of the Clinical Brain Disorders Branch at the National Institutes of Health, said the
     research is a key step in understanding the complex biological puzzle of human temperament.

     "Genes don't create personality, but they give you the building blocks. This is one building block of personality,"
     said Weinberger, director of the study published in the current issue of Science.

     Ahmad Hariri, lead author and staff fellow at the NIH, said that they have not discovered the "anxiety gene." This
     gene is part of a complex system for determining how people feel fear, added Weinberger. "There are lots of
     factors in how people react to fearful stimuli," he said. "One of those is genetic."

     The gene in question is part of the serotonin system, a brain-messaging chemical that has been implicated in mood.
     There is a naturally occurring variation in the gene -- a short form and a long form. Those with a shortened version
     have less of a protein, called the serotonin transporter, "that is like a vacuum, sucking the serotonin out of the
     synapses," Weinberger said.

     There have been some previous studies showing that people with the short form of the gene are more anxious, but
     the results are far from conclusive, Weinberger said.