Platelet monoamine oxidase activity in children and adolescents with psychiatric disorders.

Platelet monoamine oxidase (MAO) activity was studied in 108 children and adolescents with psychiatric illness and 67 control subjects. Platelet MAO activity was higher in male children with a psychiatric disturbance than in male control subjects. There was a gradual decline in platelet MAO activity during childhood and adolescence. Associations were demonstrated between MAO activity and hemoglobin, hematocrit, and platelet count, and should be considered in biological studies of vulnerability to psychiatric illness.