Platelet enzyme abnormalities in neuropsychiatric disease.

Blood platelets accumulate, store and release a variety of biogenic amines including norepinephrine, serotonin and dopamine (DA) which are known to act as neurotransmitter substances. Platelet monoamine oxidase (MAO) shares many biochemical properties with the mitochondrial MAO present in brain tissue. For these reasons it has been suggested that platelets might serve as a diagnostic and research model for nerve cells in a variety of neuropsychiatric diseases. In some patients with schizophrenia and manic depressive phychoses, platelet MAO activity is significantly decreased. Central nervous system inhibition of MAO could lead to excess accumulation of monoamines in the brain; this would be consistent with the DA hypothesis of schizophrenia. Disturbances of monoamines and enzyme kinetics in the hereditary ataxias and in Huntington disease have been described, but these findings are unproven and controversal. If platelet models for human neuropsychiatric disease can be established, they will be immensely important in preclinical diagnosis, therapy and genetic counseling.