ATL1 and hereditary spastic paraplegia: Depletion or mutation of human ATL1, a dominant form in the central nervous system, causes unbranched ER at the cellular level (Hu et al., 2009) and hereditary spastic paraplegia (HSP), a neurodegenerative disease characterized by axon shortening in corticospinal motor neurons and progressive spasticity and weakness of the lower limbs, at the organism level (Zhao et al., 2001; Salinas et al., 2008).