Before the start of the NESDA and NTR biological sample collection, processing, and storage protocols were harmonized and DNA extraction was conducted concurrently in the same laboratory. For NESDA, blood sampling for the NESDA participants took place during the baseline visit (between 0830-0930) and DNA was isolated using the FlexiGene DNA AGF3000 kit (Qiagen, Valencia, CA, USA) on an AutoGenFlex 3000 workstation (Autogen, Holliston, MA, USA). For NTR, biological samples were taken in the subject's home (between 0700-1000) and DNA was extracted using the Puregene DNA isolation kit (Gentra, Minneapolis, MN, USA) for frozen whole blood samples. DNA concentrations were determined using the PicoGreen dsDNA Quantitation kit (Invitrogen Corporation, Carlsbad, CA, USA). All procedures were performed according to the manufacturer's protocols.
