ADARB2 and major depressive disorder: In the overlapped MDD genes, we found several genes with various nervous system roles such as the adenosine deaminase, Adarb2, which can edit the serotonin receptor 2C mRNA and drastically affect its affinity for serotonin binding (Di Narzo et al. 2014) and the NADPH-dependent enzyme Hsd11b1, which converts cortisone to the stress hormone cortisol (Tomlinson et al. 2004).