As noted, the GPC was designed as a multiethnic, multiracial cohort of treated patients and a population of screened ancestrally matched controls. Fourteen collaborating sites participated in the GPC, applying a standardized approach to case ascertainment and assessment. Medically confirmed cases were recruited from hospitals, clinics, group homes, and other accommodations. As noted, special efforts were put in place to recruit minority cases and controls by selecting participating sites with large numbers of minorities in treatment. The GPC thus has a unique sample of minority cases and controls, although the number currently available for discovery studies (2,000 Latino and 2,000 African ancestry subjects) needs to be enriched.
Initial participation in the GPC involved a screening questionnaire designed for the study and either administered by study staff or completed as a self-report. Both cases and controls completed the same screening questionnaire and donated a small blood sample (<50 mL). Cases were also administered a structured diagnostic interview that lasted approximately 45 minutes. Remuneration was provided to all participants. The vast majority of GPC participants (88%) gave permission to be recontacted for follow-up investigations. Future studies are being planned that include deeper phenotypic characterizations of individuals with particular genetic profiles and studies of targeted interventions and treatments.