DNA was extracted from blood samples or buccal swabs using a manual salting procedure.53 The length of the 5-HTTLPR alleles was determined by direct analysis on an automated capillary sequencer (ABI3730, Applied Biosystems, Nieuwerkerk a/d Ijssel, The Netherlands). The rs25531 single-nucleotide polymorphism genotypes (LA vs LG) were obtained using a custom-made Taqman assay (Applied Biosystems). For more details see Nederhof et al.54 The 5-HTTLPR polymorphisms were in Hardy–Weinberg equilibrium. Genotype frequencies were 24 L'L', 50 L'S' and 26% S'S'. Genotype frequencies did not vary significantly by sex (χ2=1.07, P=0.59) or ethnicity (F=1.35, P=0.26).
