An exploratory analysis based on the GAIN/IMAGE sample made use of the age of onset of hyperactive–impulsive and inattentive symptoms, as assessed with a question from the PACS interview, each, as an informative phenotype for a GWAS (Lasky-Su et al. 2008a). Earlier work of the authors had suggested that environmental exposure outside the womb were less likely to contribute significantly to the development of ADHD with a very early age of onset (Lasky-Su et al. 2007). The number of children included in the analysis was 930 with a mean age of 10.86 years, 810 of them being males. The average age at onset of ADHD symptoms was 2.67 years; for the hyperactive–impulsive symptoms this age was 2.77, for the inattentive symptoms it was 4.31 years. The study investigated 429,784 autosomal SNPs using the FBAT-logrank algorithm (Lange et al. 2004a) to identify genetic variants that could predispose children to an earlier age of onset of disease symptoms. Additive, dominant and recessive genetic models were tested. A total of 16 SNPs reached P values for association <10−5 including 14 unique findings (Table
