DNA was obtained from buccal cells using a cytology brush for collection. DNA was isolated using the InstaGene Matrix kit protocol for cell lysis absorption (Bio-Rad Laboratories, Hercules, CA, USA). Genotyping of the MAOA promoter polymorphism used samples with a working concentration of 5-20 ng/ml. Primer sequences were used as described previously (Sabol et al. 1998), specifically MAO APT1 labeled with the FAM-6 fluorophore (5′-ACAGCCTGACCGTG-GAGAAG-3′) and MAO APB1 (5′-GAACGGACGCTCCATTCGGA-3′). Polymerase chain reaction (PCR) amplification of the MAOA promoter region VNTR was performed in 96-well microtitre plates, using a 10-ml volume containing 50-200 ng of genomic DNA, 10 × PCR buffer (Invitrogen), 0.3 mM 2′-deoxynucleoside 5′-triphosphate (Invitrogen), 50 mM magnesium chloride, 0.3 mmol each of forward and reverse primer, and 0.5 U Platinum Taq DNA polymerase (Invitrogen). Cycling reactions were performed on a PTC-225 DNA engine (MJ Research Inc., Waltham, MA, USA) with a 3-min initial denaturation at 95 °C, followed by 35 cycles at 95 °C for 3 min, 62 °C for 1 min, 72 °C for 1.5 min, and concluding with a final extension at 72 °C for 8 min.
