The role of the VNTR functional polymorphism of the promoter region of the MAOA gene on psychiatric disorders

Introduction: A functional variable number of tandem repeats (VNTR) polymorphism of the promoter region of the monoamine oxidase A (MAOA) gene has been described and many studies have investigated the association of this polymorphism with human behaviors, as well as with several psychiatric disorders. Objective: This study aimed to review the literature on the role of the VNTR functional polymorphism of the promoter region of the MAOA gene on the modulation of human behavior for the development of psychiatric disorders. Method: Searches on the Medline, Embase, Web of Science and PsycInfo databases were performed including works from January 1998 to June 2009. The words used were: "MAOA and human behavior" and "MAOA and psychiatry". Results: Several studies were found (N = 3,873). After the selection process, 109 papers were included in the review. There was found an association of MAOA low activity alleles with antisocial personality disorder, conduct disorder, ADHD, pathological gambling, and substance abuse. High activity alleles were associated with neuroticism, anorexia nervosa and depression and anxiety disorders. There was no association between the MAOA polymorphisms and bipolar disorder and schizophrenia. Discussion: The main findings, summarized in this paper, support a role of MAOA VNTR polymorphism in some psychiatric disorders although some divergences were found due to methodological difficulties in genetic studies. In general, the studies associated the low activity alleles with impulsivity and aggressive behavior ("hyperactive behaviors"), and the high activity alleles of the gene with "hypoactive behaviors", such as depression and anxiety, which demonstrates a modulation of the MAOA enzyme in "hyperactive" and "hypoactive" disorders.