Dual effect of α-synuclein disease variants on condensate formation

α-synuclein is a pre-synaptic protein ^1,2 implicated in synucleinopathies like Parkinson’s disease and Dementia with Lewy Bodies, where it accumulates in intracellular aggregates termed Lewy bodies and Lewy neurites ³ . Recent studies have reported that α-synuclein undergoes phase separation to form biomolecular condensates both in vitro and in mammalian cells ^4–7 . α-synuclein condensates are thought to contribute to disease through progressive aggregation ^5,8,9 . 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 familial disease, E46K and E83Q, enhance condensate formation in vitro and in cells. However, variants including A30G, G51D, and A53E fail to form or have reduced levels of condensate formation in cells. The same phenotypes are reflected in the budding yeast model showing differential inclusion formation. In iPSC-derived neurons, the propensity of α-synuclein variants to undergo VAMP2-mediated phase separation reflects the level of synaptic enrichment. We show that the intrinsic propensity of α-synuclein to form condensates and the ability to bind lipid membranes are important to mediate condensate formation in cells. Our results emphasize that α-synuclein pathology follows divergent pathways, with both increased and decreased condensate formation contributing to disease. This study establishes biomolecular condensates as a key intermediate in α-synuclein dysfunction, providing a novel foundation for translational research.