MDD cases were mainly from NESDA, a longitudinal cohort study designed to be representative of individuals with depressive and/or anxiety disorders. Recruitment of participants for NESDA took place from 09/2004-02/2007, and ascertainment was from outpatient specialist mental health facilities and via primary care screening. Additional cases were from the population-based cohorts NEMESIS (25), ARIADNE (26), and the NTR. Regardless of recruitment setting, similar inclusion and exclusion criteria were used to select MDD cases. Inclusion criteria were a lifetime diagnosis of DSM-IV MDD (1) as diagnosed via the Composite International Diagnostic Interview psychiatric interview (27), age 18-65 years, and self-reported western European ancestry. Persons who were not fluent in Dutch and those with a primary diagnosis of schizophrenia or schizoaffective disorder, obsessive compulsive disorder, bipolar disorder, or severe substance use dependence were excluded (the etiology of MDD in these subjects may be distinct). The 1,862 cases included in GAIN were recruited from mental health care organizations (N=785), primary care (N=603), and community samples (NEMESIS N=218, ARIADNE N=96 and NTR N=160).
