NEFL and cerebellar ataxia: Gradual motor decline (balance and coordination tests worsen over months of exposure: falling off rotarod, widened gait) and an age-dependent rise in blood and CSF neurofilament light (NfL) levels; chronic diet lead to persistent mild ataxia and tremor; broad-based, unsteady gait; enhanced GABA_A signaling, reduced cerebellar metabolic activity; vermis atrophy (selective shrinkage of anterior lobules);