SNCA and Parkinson disease: It is also possible that TBI may advance or alter a pre-existing neurodegeneration cascade [28]; for example, variability in the gene encoding α-synuclein has been associated with an increased risk of developing PD after TBI, such that the increased levels of α-synuclein seen post-TBI could further the development of PD in someone with said genetic variability [114,118,119,120].