A 45-year-old woman presents to neurology clinic with a 2-year history of progressive involuntary jerky movements, cognitive decline, and mood disturbances. She reports her father died at age 52 with dementia and similar movement abnormalities. On examination, she demonstrates choreiform movements of the upper extremities, emotional lability, and mild cognitive slowing on mental status testing. Brain MRI shows bilateral caudate nucleus atrophy with preserved cortical volume. Genetic testing confirms a CAG trinucleotide repeat expansion in the HTT gene (45 repeats; normal <27). Which of the following best explains the primary neuropathology underlying her clinical syndrome?

1. A)Selective loss of GABAergic neurons in the striatum leading to relative overactivity of thalamocortical pathwaysGABARITO
2. B)Preferential degeneration of dopaminergic neurons in the substantia nigra pars compacta
3. C)Calcium-mediated excitotoxicity from excessive glutamate signaling at N-methyl-D-aspartate receptors
4. D)Depletion of acetylcholine-producing neurons in the nucleus basalis of Meynert
5. E)Loss of serotonergic projections from the dorsal raphe nucleus to the prefrontal cortex