At Wave IV (2008-2009), Add Health expanded its saliva DNA collection to include the entire sample of Add Health participants (N = 15,701), affording greater statistical power for genetic analyses, especially gene x environment interactions, and opportunities for replication. Saliva was collected using the Oragene collection method (Oragene™, DNAgenotek, Ottawa, Ontario, Canada) and genomic DNA isolated from the Oragene™ solutions using ZymoResearch (Irvine, CA). Consent rates for Wave IV DNA collection were high; 96% of all sibling pairs consented to provide saliva for DNA extraction, and there was little variation by type of genetic relatedness (similar to the consent rate for all Wave IV respondents, see “Add Health Wave IV Documentation: Candidate Genes” at http://www.cpc.unc.edu/projects/addhealth/data/guides/DNA_documentation.pdf). The Wave IV Program Project was budgeted to genotype ten candidate loci and a panel of SNPs in at least five of the following candidate genes: the dopamine transporter (DAT1, locus symbol SLC6A3); dopamine D4 receptor (DRD4); dopamine D2 receptor (DRD2); serotonin transporter (5HTT, locus symbol SLC6A4); serotonin 2A receptor (5-HT2A); Monoamine Oxidase A promoter (MAOA-uVNTR); Monoamine Oxidase A STR (MAOA[GT]n); dopamine D5 receptor (DRD5);
