MAPK8 and proximal spinal muscular atrophy: Thus, we will focus on JNK roles in three different pathologies affecting MNs: amyotrophic lateral sclerosis (ALS), commonly diagnosed in middle and late adulthood, spinal muscular atrophy (SMA), which occurs in early childhood (Figure 4), and the spinal and bulbar muscular atrophy, an adult-onset disorder characterized not only by the degeneration of spinal MNs, but also of those in the brainstem.