Genetic variants of the monoamine oxidase A (MAOA) have been associated with 
aggression-, anxiety-, and addiction-related behavior in several nonclinical and 
clinical populations. Here, we investigated the influence of allelic variation 
of MAOA activity on aggression-related personality traits and disease risk in 
patients with personality disorders. Personality disorders were diagnosed with 
the Structured Clinical Interview of DSM-IV and were allocated to cluster A, B, 
and C. Personality features were assessed by the revised NEO Personality 
Inventory and the Tridimensional Personality Questionnaire. The genotype of the 
MAOA gene-linked polymorphic region (MAOA-LPR) was determined in 566 patients 
with personality disorders and in 281 healthy controls. MAOA genotype was 
significantly associated with cluster B personality disorders (chi2=7.77, 
p=0.005, df=1) but not with cluster C personality disorders. In total, 26.0% of 
cluster B patients were hemi- or homozygous for the low-activity variant of the 
MAOA genotype, compared to 16.4% in the control group. Associations between MAOA 
variants and personality domains related to impulsivity and aggressiveness were 
inconsistent. Our findings further support the notion that allelic variation of 
MAOA activity contributes modestly to the balance of hyper- 
(impulsive-aggressive) and hyporeactive (anxious-depressive) traits.