1. Laboratory of The Biology of Addictive Diseases, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
2. Department of Psychiatry, Amsterdam Institute for Addiction Research, Academic Medical Center, University of Amsterdam, PO Box 22660, 1100DD Amsterdam, The Netherlands
3. Parnassia Addiction Research Centre (Brijder Addiction Treatment), PO Box 53002, 2505 AA The Hague, The Netherlands
4. Brain Center Rudolf Magnus, University Medical Center, Utrecht University, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands
5. Laboratory of Statistical Genetics, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA