It's associated with...

Anxiety like behavior..
Restless leg syndrome, panic disorder, bio-polar affective disorder, implications for Norrie Disease, aggressive Behavior violence, delinquent behavior in adolescence and young adults.
And we know also in Autism and ADHD..

Mercury can effect brain serotonin and cause aggressive behavior too..
This is interesting..
Got to read up more on this.

ADHD Treatments..

http://adhd-treatment-options.blogspot.com/2009/03/adhd-gender-and-maoa-gene.html

... Brunner's syndrome involves an MAO-A deficiency, .... or failure to distinguish autism from ADHD, obsessive compulsive disorder, ...

Or OCD too..

http://linkinghub.elsevier.com/retrieve/pii/S0006322398003199

Mutations in genes coding for monamine oxidase A (MAO-A), a mitochondrial enzyme which oxidizes 5HT, dopamine and norepinephrine..

http://neuro.psychiatryonline.org/cgi/content/full/18/1/86

There is something that may be helpfull here in difficult to treat cases and relations to other like conditions.