Platelet monoamine oxidase activity in Huntington's chorea

SUMMARY The possibility that genetically determined abnormalities in the monoamine oxidase of certain central nervous system aminergic neurones may play a part in the pathology of Huntington's chorea was investigated using human platelet monoamine oxidase. Significantly elevated monoamine oxidase activity was found in male patients compared to control subjects suggesting this may be a screening test for this disorder. Low monoamine oxidase activity was associated with a better clinical response to drugs. Huntington's chorea is an autosomal dominant degenerative central nervous disorder producing chorea and dementia. The disorder has been con-sidered the "opposite " motor lesion to Parkinson's disease. The principal neuropathology involves degeneration of the basal ganglia, particularly the caudate nucleus, affecting the small interneurones, Golgi type 2 (Bruyn, 1968). The neurochemical changes involve findings in three neurotransmitter systems: amine, gamma aminobutyric acid (GABA), and cholinergic. Attempts to find reproducible abnormalities of amines, particularly dopamine and 5-hydroxy-tryptamine (5-HT) have failed (Bernheimer and Hornykiewicz, 1973; Chase, 1973; Bird and Iversen, 1974). Evidence from drug effects is more suggestive. Dopamine competitive inhibitors, such as haloperidol, and dopamine depleters, such as reserpine and tetrabenazine, improve choreatic movements temporarily, and this suggests that there is relative overactivity of the dopaminergic system. Decreased levels of GABA and its biosynthetic enzyme, glutamine acid decarboxylase (GAD) have been reported (Bird et al., 1973; Iversen et al., 1974; Urquhart et al., 1975). Degeneration of the small cholinergic interneurones of the corpus striatum and low levels of choline acetyltransferase have been found in choreatic brains at post