It is characterized by lower than average IQ (typically about 85), problematic impulsive behavior (such as pyromania, hypersexuality and violence), sleep disorders and mood swings.

There is no restrictive treatment for Brunner syndrome, although a potential treatment can be established by checking the patient for signs and symptoms and analysing different catabolites in bodily fluids, that would be indicative of excess amount of monoamines in the body and mediating the symptoms by targeting therapy for the most problematic neurotransmitter.

Brunner and his colleagues upon the discovery of a particular genetic defect in male members of a large Dutch family.

[6] Brunner found that all of the male family members with this defect reacted aggressively when angry, fearful, or frustrated.

[6] Brunner said that an "MAO-A deficiency is associated with a recognizable behavioural phenotype that included disturbed regulation of impulsive aggression".