Over 50% of cases of pure AD-HSP are caused by mutations in spastin (Hazan et al., 1999), which encodes one of a small family of microtubule-severing proteins – hexameric ATPases that disassemble microtubules along their length (Roll-Mecak and McNally, 2010; Sharp and Ross, 2012). Here, SPAST is linked to hereditary spastic paraplegia.