In the PGC GWAMA, MDD was established with structured clinical interviews (e.g., Clinical Interview Schedule-Revised, Diagnostic Interview for Genetic Studies, and the Structured Clinical Interview for DSM-IV). All clinical evaluations were made by experienced clinicians/interviewers. Most cases were ascertained from clinical sources. Controls were screened in most of the studies to require the absence of MDD and recruited from the general population. Full details about the PGC samples can be found in the previous publication (7). In the CHARGE GWAMA, depressive symptoms were assessed with validated questionnaires. Measures include the Center for Epidemiological Studies-Depression (CES-D) scale, Geriatric Depression Scale (GDS), Patient Health Questionnaire-9, and the Beck Depression Inventory-II (BDI-II) mostly assessing depressive symptoms in previous weeks rather than lifetime MDD (14). Persons with schizophrenia, bipolar disorder, and dementia were excluded. Persons aged 40 and older and with genotype data and depressive symptom score were included.
