# Lewy body / α-synuclein

Lewy bodies are clumps that build up inside your brain cells, made mostly of a misfolded protein called α-synuclein. Friedrich Lewy first described them in 1912, and they are the defining feature of Parkinson's disease, dementia with Lewy bodies (DLB), and Parkinson's disease dementia. Normally α-synuclein (made by the SNCA gene) helps shuttle dopamine-carrying vesicles at the connections between neurons. But under the wrong conditions (extra copies or mutations of SNCA, oxidative stress, broken autophagy and lysosome problems), it misfolds and sticks to itself, first into small clusters and then into amyloid-like fibers. These can spread from neuron to neuron in a prion-like way, matching how Parkinson's pathology fans out across the brain (Braak's staging). Is α-synuclein the root cause of the nerve damage, or a downstream symptom? It is debated. But the fact that extra SNCA copies cause inherited Parkinson's, and that the small clusters are toxic in lab models, points toward a causal role. In DLB (the second most common neurodegenerative dementia) the pathology produces fluctuating thinking, visual hallucinations, acting out dreams (REM sleep behavior disorder), and parkinsonism, often alongside Alzheimer's changes.

## Sources

- Spillantini MG, Schmidt ML, Lee VM, Trojanowski JQ, Jakes R, Goedert M. (1997). Alpha-synuclein in Lewy bodies. Nature. https://doi.org/10.1038/42166
- Spillantini MG, Crowther RA, Jakes R, Hasegawa M, Goedert M. (1998). Alpha-synuclein in filamentous inclusions of Lewy bodies from Parkinson's disease and dementia with Lewy bodies. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.95.11.6469

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