TPPP and Parkinson disease: The pathophysiology of the assembly/aggregation of SYN resulting from interaction with TPPP is a complex process that is yet to be understood in detail; this incomplete understanding comes from the fact that the two proteins are significantly co-enriched and co-located in inclusions in neurons (PD and DLB) and OLGs (MSA) whilst still being expressed endogenously in two different cell types of the normal human brain [17,31,32,33].