For most individuals, the pathology of Parkinson's and Alzheimer's disease begins in the nose with misfolded protein and spreads backwards into the brain.
"And the pathology, for most individuals the pathology of both these diseases begins in the nose with misfolded protein and then spreads backwards to the parts of the brain that control motor function in Parkinson's, and backwards to the part of the brain that controls memory in Alzheimer's disease." (said at 0:32:02)
The speaker states as an established fact that for 'most individuals' pathology begins in the nose with misfolded protein and spreads into the brain for both Parkinson's and Alzheimer's disease. While early olfactory involvement and smell deficits are well documented in both disorders, an initial nasal origin is a theoretical model (the olfactory vector hypothesis / Braak dual-hit hypothesis) rather than a confirmed universal pathway. In Parkinson's disease, Lewy pathology is hypothesized to originate either in the enteric nervous system (gut-first) or the olfactory bulb/dorsal motor nucleus (brain-first). In Alzheimer's disease, classical neuropathological staging (Braak and Thal staging) typically identifies the earliest hyperphosphorylated tau lesions in the locus coeruleus/transentorhinal cortex and amyloid-beta in neocortical regions, not the nasal mucosa. Presenting nasal initiation as the established mechanism for most cases of both diseases is therefore an overstatement.
- context: The olfactory vector hypothesis of neurodegenerative disease: is it viable? (Annals of neurology 2008)
"The presence of smell loss and the pathological involvement of the olfactory pathways in the formative stages of Alzheimer's and Parkinson's diseases, together with evidence that xenobiotics, some epidemiologically linked to these diseases, can readily enter the brain via the olfactory mucosa, have led to the hypothesis that Alzheimer's and Parkinson's diseases may be caused or catalyzed by agents that enter the brain via this route." (abstract, review, passage verified)
pubmedfull study (doi) - context: Olfactory bulb involvement in neurodegenerative diseases. (Acta neuropathologica 2014)
"Olfactory dysfunction is a common and early symptom of many neurodegenerative diseases, particularly of Parkinson's disease and other synucleinopathies, Alzheimer's disease (AD), and mild cognitive impairment heralding its progression to dementia." (abstract, results, passage verified)
pubmedfull study (doi) - partial: Pathogenesis of Parkinson disease--the gut-brain axis and environmental factors. (Nature reviews. Neurology 2015)
"The neuropathological process that leads to PD seems to start in the ENS or the olfactory bulb and spreads via rostrocranial transmission to the substantia nigra and further into the CNS, raising the intriguing possibility that environmental substances can trigger pathogenesis." (abstract, results/conclusions, passage verified)
pubmedfull study (doi)