[Hyperbranching axons template α-synuclein deposits and non-localizing clinical manifestations of Parkinson disease].

The "proteinopathy" hypothesis, which states that pathological inclusions result in neuronal death, is classically invoked to explain neurodegeneration. In this review on α-synuclein (αS), attention is shifted to the distal axons, where αS deposits earlier than in the cytoplasmic formation of Lewy bodies (LBs). Because LBs are preferentially formed in axons with abundant branching, hyperbranching may accentuate axonal degeneration and αS deposition in their distal ends. This hyperbranching may also explain why motor/non-motor symptoms of Parkinson disease (PD) are so generalized and diffuse with barely any localizing value. Such underlying structure templates both the distal-dominant degeneration with αS deposition, and the non-localizing nature of clinical manifestations of PD, and as such can be considered a "structural template" thereof. The evolution of PD symptoms can be highly variable, ranging from restricted LB lesions and corresponding, long-lived, symptoms (pure autonomic failure, cardiac denervation, essential tremor, and REM-related behavioral disorders, which may be collectively called "focal LB disease") to the more haphazard appearance of dementia or anosmia without developing parkinsonism or brainstem lesions. This variability is better explained by the parallel involvement of multiple systems with hyperbranching axons rather than the stereotyped upward spread of LB in the brainstem. Awareness of presynaptic dysfunctions of these hyperbranching systems may enhance the sensitivity and specificity of clinical diagnoses of PD for earlier therapeutic intervention.