Human α-synuclein (either the wildtype or the A53T mutant form), associated with a dominant form of PD (Polymeropoulos, 1997), did not show any protection under the 9 mM MTZ treatment condition; mis-expression of the A53T mutant form of α-synuclein significantly worsened DA neuron integrity under the milder 4.5 mM MTZ treatment condition (Figure 1L–M). Here, SNCA is linked to Parkinson disease.