SLC9A9 and attention deficit-hyperactivity disorder: GWAS in ADHD have shown suggestive evidence for association of cadherin 13 (CDH13) and other candidate genes, including monoamine system-related genes (e.g. SLC9A9 and SNAP25), the glutamate metabotropic receptor 5 (GRM5), the glucose-fructose oxidoreductase domain containing 1 (GFOD1), the cannabinoid receptor 1 (CNR1), the protein kinase CGMP-dependent 1 (PRKG1) or the nicotinic acetylcholine receptor alpha 7 (CHRNA7), among others2–4, 8.