consistent findings in genome-wide studies on a wide variety of phenotypes related to drug abuse and dependence (Uhl et al. 2008a, b), although there is no clear indication, which region of the gene is most important. Possibly, different regions or risk factors might cause different phenotypes. CDH13 codes for cadherin 13 (or T-cadherin), a member of a family of cell–cell adhesion proteins (Patel et al. 2003), in addition to being a regulator of neural cell growth. CDH13 shows a brain expression profile consistent with a role in ADHD, being expressed in regions showing volumetric reductions in patients with this disorder (Takeuchi et al. 2000; Takeuchi and Ohtsuki 2001; Valera et al. 2007). Very little is known about the second associated gene, GFOD1 and its product, glucose–fructose oxidoreductase-domain containing 1, except that it is expressed in brain and possibly plays a role in electron transport (Lasky-Su et al. 2008b).
