MMP9 and Parkinson disease: Although only significant when considering such a large number of genes, the genes annotated with a role in extracellular matrix disassembly include those encoding the metalloproteinases MMP-7 and MMP-8, and the reduced expression of metalloproteinases has been noted in PD post-mortem brain tissue15 while a polymorphism in MMP-9 has been associated with PD and amyotrophic lateral sclerosis16.