Two major therapeutic categories of MAOI: the MAO-A inhibitors in certain mental disorders such as depression and anxiety (Amrein et al., 1999[2]) and MAO-B inhibitors proved their remedial value in neurodegenerative diseases (Youdim et al., 2006[45]; Foley et al., 2000[10]) including Parkinson's (Cesura and Pletscher, 1992[5]) and Alzheimer's (Volz and Gleiter, 1998[43]). This evidence concerns the gene MAOA and psychiatric disorder.