As compared to the nonselective-irreversible MAO-A and MAO-B inhibitors (MAO-Is) which were initially used with severe side effects for treating depression [69], the present selective and reversible inhibitors of MAO-A and MAO-B are rather more useful for treating depression, anxiety as well as coadjuvant agents in the treatment of Parkinson’s and Alzheimer’s disease [70]. This evidence concerns the gene MAOA and major depressive disorder.