Astrocytes in the ventral spinal cord can be distinguished from astrocytes in the dorsal spinal cord by expression of semaphorin A3 (Sema3a), which is implicated in the specific vulnerability to FF-MNs in ALS (see section “Neuroprotective and Neurotoxic Factor Expression in MN Subpopulations” below). This evidence concerns the gene SEMA3A and amyotrophic lateral sclerosis.