A 35-year-old woman presents to neurology with a 2-year history of progressive involuntary jerking movements of her arms and legs, facial grimacing, and difficulty with voluntary movement initiation. She reports declining performance at work, increased irritability, and poor concentration. Her father died at age 55 with similar symptoms. On examination, she has choreiform movements that worsen with stress and disappear during sleep. Brain MRI shows generalized cerebral atrophy with particular involvement of the caudate and putamen. Genetic testing confirms an expanded CAG trinucleotide repeat (>40 repeats). Which of the following best explains the primary neuropathological mechanism underlying her clinical presentation?

1. A)Selective loss of medium spiny neurons in the striatum with disruption of the indirect motor pathwayGABARITO
2. B)Degeneration of cholinergic interneurons leading to unopposed acetylcholine activity
3. C)Excitotoxic neuronal death from sustained glutamate receptor activation
4. D)Loss of serotonergic neurons in the raphe nuclei causing mood and motor dysregulation
5. E)Depletion of GABA-producing neurons in the substantia nigra pars reticulata