Presynaptic dysfunction in Huntington's disease.

HD (Huntington's disease) is produced by the expression of mutant forms of the protein htt (huntingtin) containing a pathologically expanded poly-glutamine repeat. For unknown reasons, in HD patients and HD mouse models, neurons from the striatum and cerebral cortex degenerate and lead to motor dysfunction and dementia. Synaptic transmission in those neurons becomes progressively altered during the course of the disease. However, the relationship between synaptic dysfunction and neurodegeneration in HD is not yet clear. Are there early specific functional synaptic changes preceding symptoms and neurodegeneration? What is the role of those changes in neuronal damage? Recent experiments in a Drosophila model of HD have showed that abnormally increased neurotransmitter release might be a leading cause of neurodegeneration. In the present review, we summarize recently described synaptic alterations in HD animal models and discuss potential underlying molecular mechanisms.