For example, Sarm1 and Nmnat2 contribute to axonal degeneration—a critical, early event in neurodegenerative diseases 42, 43, while Unc13a, Vgf, Rtn2, Lrp11 and Rundc3a have been implicated in amyotrophic lateral sclerosis 44, frontotemporal dementia 45, hereditary spastic paraplegias 46, and Parkinson's disease and AD 47, 48, 49. This evidence concerns the gene NMNAT2 and hereditary spastic paraplegia.