Human monoamine oxidase: from genetic variation to complex human phenotypes

Monoamine oxidases A and B (MAOA and MAOB) have been suggested to be involved in human behavior and neuropsychiatric disorders. These observations were supported by several lines of evidence provided by pharmacological studies as well as enzyme deficiency investigations in humans and model animals. Numerous allelic association studies have attempted to detect a link between different alleles of the genes encoding monoamine oxidases and certain complex human traits. Many of these studies have reported contradictory findings, probably due to population stratification and limitations of the experimental and statistical designs used in the studies. Here, we review all the genetic variants described for the MAO genes, we summarize the allelic associations found with different traits, and we discuss these results in the context of the factors that affect detection of allelic association. Finally, we discuss the advantages of the use of haplotypes for studying associations with human traits.