This study from Okinawa suggests that alpha synuclein changes the way in which endocytosis works in neurons, disrupting neurotransmission.

I thought it was interesting because it suggests a mechanism of action of over-expressed alpha synuclein causing diminished neurotransmission.

Note that this is not an explanation of neuron death, which is thought to be caused by programmed cell death (apoptosis) when the cell's functionality is impaired. But it may be an explanation for the cause of the impairment itself.

Dan