For the DAT1 VNTR, total genomic DNA (60 ng) was combined with 1× MBI Fermentas PCR buffer containing KCl, 1.5 mM MgCl (MBI Fermentas), 0.13 μg each primer (forward primer labeled with 5′ NED fluorescent tag), 10% DMSO (Sigma-Aldrich), 0.16 mM each dNTP (MBI Fermentas) and 2 U Taq polymerase (MBIFermentas) to a total volume of 25 μl in a 96-well PCR plate.