SMN2 and proximal spinal muscular atrophy: As a result, indirect markers of axon degeneration are released by suffering motor neuron and detectable in CSF and bloodstream, such as phosphorylated neurofilament heavy chain (pNfH) and neurofilament light chain (NfL), which are increased both in pre-symptomatic SMA patients with 2 SMN2 copies and symptomatic SMA patients [10, 44–46].