DNA was collected from CDP participants from February 2006 to July 2007. For many participants, DNA collection took place at an annual follow-up visit. Following completion of phenotypic assessments, participants were invited to provide a DNA sample. However for some participants, especially for the considerable number who lived away from the main research offices, DNA was collected in the context of a special visit. DNA was collected via saliva sample using Oragene collection kits, under the supervision of a specially trained interviewer. Participants received an additional $20 for participating in the DNA collection portion of the project and provided separate consent for the genotyping component of the project. Saliva samples were subsequently labeled anonymously and mailed to the laboratory of Dr. Alison Goate at Washington University, St. Louis, where DNA extraction and genotyping occurred. DNA samples were obtained from 452 individuals (52% female), representing 91% of those participants who were able to be contacted: 378 European Americans, 64 African Americans, and 10 individuals of other ethnic origin. Institutional Review Boards at each site approved this project.
