Hyperkinetic manifestations in sporadic parkinsonism: An exploratory case series with APOE and NOS3 variants.

Background Hyperkinetic motor features are uncommon in Parkinson's disease and related parkinsonisms and may reflect underlying genetic susceptibility. Methods We describe three sporadic patients with parkinsonism and prominent hyperkinetic manifestations who underwent clinical exome sequencing. To provide preliminary context for these observations, we reviewed genetic data from an additional cohort of 11 patients with sporadic parkinsonism who underwent clinical exome sequencing in our center but did not exhibit early hyperkinetic manifestations Results All patients carried heterozygous variants in genes involved in vascular, inflammatory, and tau related pathways (NOS3 c.774 T > C; APOE c.388 T > C). Clinical phenotypes ranged from late-onset parkinsonism with severe choreic dyskinesias to young-onset dystonic parkinsonism with excellent dopaminergic responsiveness. Dopaminergic dysfunction was supported by functional neuroimaging. Conclusions These cases suggest that APOE and NOS3 variants may act as susceptibility modifiers, predisposing to hyperkinetic phenotypes within the parkinsonian spectrum.