Is a circulating neurotoxin involved in the pathogenesis of Huntington's chorea?

We tested the hypothesis that the premature neuronal death which occurs in Huntington's chorea (HC) might be the result of a genetically-determined enzymatic failure in the degradation of a circulating neurotoxin of either endogenous of exogenous origin. Infant rats were given daily subcutaneous injections of large quantities of whole serum (for 24 days), or of a concentrated serum ultrafiltrate (for 37 days), obtained from HC patients or control subjects. Animals were killed 4 months after the end of injections, and their striata were examined neurochemically. There was a significant but small (16%) reduction in the mean striatal content of gamma-aminobutyric acid (GABA) in rats treated with whole serum from HC patients, but no striatal GABA deficiency was observed in rats treated with ultrafiltrates of serum from HC patients. Nor did these rats have any reduction in their striatal choline acetyltransferase activity. We conclude that if a circulating neurotoxin does contribute to the pathogenesis of HC, it must either be a small molecule which is tightly bound to serum proteins, or less likely a large compound with a molecular weight greater than 10 000.