A microarray study on the time-course of acute response to nicotine in the VTA of mice showed that RhoA expression levels increased significantly with the duration of nicotine treatment, and one SNP of RhoA gene, rs2878298, showed a highly significant genotypic association with the initiation of smoking and nicotine dependence (Chen et al., 2007). The gene discussed is RHOA; the disease is nicotine dependence.