The MAO-A gene plays a critical role in breaking down brain chemicals like serotonin and dopamine, which influence mood and behavior. When both MAO-A and MAO-B genes are missing due to a rare genetic deletion, it causes severe developmental challenges, intellectual disabilities, and autism-like behaviors. A loss of only the MAO-A gene results in Brunner Syndrome, a rare condition characterized by mild intellectual disabilities, increased aggression, and some autism traits. In contrast, losing the MAO-B gene alone does not appear to cause behavioral issues.
A common variation of the MAO-A gene, called a variable-number tandem repeat (uVNTR), affects how much of the MAO-A enzyme is produced. The two most common forms are the “3-repeat” (low-activity) and “4-repeat” (high-activity) versions. Boys with the 3-repeat form often show more aggression and struggle with emotional control, particularly if they’ve experienced childhood trauma. For example, one study found that prisoners convicted of violent crimes were more likely to carry the 3-repeat version compared to those convicted of non-violent crimes. Boys with this low-activity gene variant have also been linked to lower IQ scores and more severe autism symptoms.
Research suggests that this low-activity gene variant may influence brain development, leading to structural differences in areas of the brain. For instance, boys with autism and the 3-repeat variant often show higher levels of brain chemicals like serotonin, which can impact behavior and emotional regulation.
Understanding MAO-A gene variations helps researchers uncover how genetics shape behavior, brain development, and conditions like autism. This knowledge could one day lead to better treatments and support for those affected.