REEP1 and neurodegenerative disease: Notably, REEP1, a neuro-enriched REEP protein, and its interaction with ATL1 has been shown to be important for maintaining ER tubular membrane in corticospinal neurons; defects in ER organization and this REEP1-ATL1 interaction have been shown to be the predominant pathogenic mechanism of hereditary spastic paraplegia, a neurodegenerative disease of the upper motor neurons.