Dual effect of α-synuclein disease variants on condensate formation.

α-synuclein is a pre-synaptic protein implicated in synucleinopathies including Parkinson's disease, Parkinson's disease dementia, and dementia with Lewy bodies, where it accumulates in intracellular aggregates termed Lewy bodies and Lewy neurites. Recent studies have reported that α-synuclein undergoes phase separation to form biomolecular condensates both in vitro and in mammalian cells. α-synuclein condensates are thought to contribute to disease through progressive aggregation. Here we show that specific PD-associated α-synuclein variants fail to form biomolecular condensates. We demonstrate that only two α-synuclein variants associated with disease, E46K and E83Q, enhance condensate formation. While other α-synuclein disease variants including A30G, G51D, and A53E fail to form condensates in cells. In iPSC-derived neurons, the extent of synaptic enrichment of different α-synuclein variants is linked to their propensity to undergo VAMP2-mediated phase separation. Our results emphasize that α-synuclein dysfunction may follow divergent pathways, with both increased and decreased condensate formation.