The unique N-terminal region of spastin-M1 contains a hydrophobic motif required for ER membrane association, and for molecular interaction with binding partner molecules receptor expression enhancing protein 1 (REEP1) and atlastin-1, which mediate ER fusion (atlastin-1) and morphology (REEP1) (Hu et al., 2009; Orso et al., 2009; Park et al., 2010); both of these molecules are also mutated to cause forms of HSP. This evidence concerns the gene ATL1 and hereditary spastic paraplegia.