BDNF and Huntington disease: The etiology of neuronal loss in HD has not been fully elucidated, and therefore, several mechanisms have been proposed to contribute to neuronal dysfunction and death in the HD brain, including oxidative stress, synaptic dysfunction, and neurotransmitter dysregulation (e.g., glutamate-mediated excitotoxicity and dopamine-mediated toxicity), as well as a decrease in trophic support (namely, a reduction in BDNF levels; for review, see [107]).