1. A method for diagnosing an anxiety disorder in a subject, comprising:a. collecting a DNA sample from the subject;
b. analyzing the DNA sample for the presence of a SNP in a PAC1 receptor gene and/or for epigenetic methylation at a first site within a ADCYAP1R1 CpG island;
c. diagnosing the anxiety disorder in the subject having the SNP in the PAC1 receptor gene and/or having elevated levels of epigenetic methylation; and
d. administering a therapeutically effective amount of a PACAP inhibitor or PACAP receptor antagonist.