Human brain function is mediated by biochemical processes, many of which can be 
visualized and quantified by positron emission tomography (PET). PET brain 
imaging of monoamine oxidase A (MAO A)-an enzyme metabolizing 
neurotransmitters-revealed that MAO A levels vary widely between healthy men and 
this variability was not explained by the common MAOA genotype (VNTR genotype), 
suggesting that environmental factors, through epigenetic modifications, may 
mediate it. Here, we analyzed MAOA methylation in white blood cells (by 
bisulphite conversion of genomic DNA and subsequent sequencing of cloned DNA 
products) and measured brain MAO A levels (using PET and [(11)C]clorgyline, a 
radiotracer with specificity for MAO A) in 34 healthy non-smoking male 
volunteers. We found significant interindividual differences in methylation 
status and methylation patterns of the core MAOA promoter. The VNTR genotype did 
not influence the methylation status of the gene or brain MAO A activity. In 
contrast, we found a robust association of the regional and CpG site-specific 
methylation of the core MAOA promoter with brain MAO A levels. These results 
suggest that the methylation status of the MAOA promoter (detected in white 
blood cells) can reliably predict the brain endophenotype. Therefore, the status 
of MAOA methylation observed in healthy males merits consideration as a variable 
contributing to interindividual differences in behavior.