Study to Identify the Genetic Variations Associated With Phantom Limb Pain

Chronic PLP Group: * At least 18 years of age. * Written informed consent and written authorization for use or release of health and research study information * Single or multiple upper and/or lower limb amputation * At least three months post-amputation * Ability to follow study instructions and likely to complete required visit(s) * Experienced PLP for at least one month and at least 3 times per week * Phantom limb pain differentiated from residual limb pain by physical exam. * Subjects taking blood thinners or other medications that do not increase risk during a blood draw. Non-Chronic PLP Group: * At least 18 years of age. * Written informed consent and written authorization for use or release of health and research study information * Single or multiple upper and/or lower limb(s) amputation * At least three months post-amputation * Ability to follow study instructions and likely to complete required visit(s) * Experienced PLP less than 10 times total and/or for less than two weeks * Subjects taking blood thinners or other medications that do not increase risk during a blood draw.