Children provided buccal cells for DNA collection via Oragene kits from DNA Genotek (Ottawa, ON, Canada). Genomic DNA was collected and isolated using standard salting out and solvent precipitation methods. The 5-HTTLPR alleles were assayed42 and modified by using primers reported by Hu et al.43 The rs25531 single-nucleotide polymorphism genotypes (LA vs LG) were obtained by incubating the PCR products with MspI.44 Samples were analyzed on an ABI PRISM 3130xl Sequencer (Carlsbad, CA, USA). Three groups of participants were formed based on their genotyping: children homozygous for the higher expressing LA allele (L'L'), children heterozygous for the lower expressing alleles (S'S') and those heterozygous (L'S'). The 5-HTTLPR polymorphisms were in Hardy–Weinberg equilibrium. Genotype frequencies were 20 L'L', 47 L'S' and 32% S'S'. Genotype frequencies did not vary significantly by race (χ2=1.42, P=0.23) or sex (χ2=0.67, P=0.41).
