Trace acid levels in the plasma and MAO activity in the platelets of violent offenders.

The plasma concentrations of the unconjugated and conjugated so-called "trace acids," phenylacetic acid (PAA), m- and p-hydroxyphenylacetic acid (mHPA, pHPA), and platelet monoamine oxidase (MAO) activity were measured in 103 male prisoners detained in a psychiatric institution. Twenty-three had been convicted of violent crimes, 18 of sexual offenses, 24 of armed robbery, 27 of nonviolent property offenses, and 11 of miscellaneous nonviolent offenses. Unconjugated pHPA and conjugated PAA were found to be significantly reduced in the violent offenders when compared with those of the "nonviolent" groups. The levels of pHPA were also found to be low in sexual offenders. Platelet MAO activities to phenylethylamine, tryptamine, and p-tyramine between any of the categories of prisoners were not significantly different.