may reflect true differences in the specific genes within pathways implicated by SNPs and CNVs, perhaps arising from the different mutational mechanisms responsible for generating large CNVs and SNPs, neither of which occur randomly with respect to the genomic sequence context. However, it is also likely that it reflects low power to identify specific risk genes. Although not supported at a genome-wide level of significance, the convergence of SNP and CNV association at CHRNA7, which encodes the cholinergic receptor nicotinic alpha 7, is intriguing. CHRNA7 is widely expressed in the brain, especially the hippocampus (34), and is involved in rapid synaptic transmission. CHRNA7 has been examined in relation to schizophrenia, associated cognitive deficits, and nicotine dependence (35, 36), although findings have not been entirely consistent. There has been little published work on ADHD, although incomplete evaluations of the gene in much smaller samples have not been supportive (37). Thus, to date this gene has yet to be comprehensively investigated in relation to ADHD.
