SPAST and hereditary spastic paraplegia: Among them, spastin is encoded by the SPAST gene, which is mutated in the most common form of dominant hereditary spastic paraplegia (HSP), a progressive neurological disease characterized by the dying-back of the long corticospinal axons (Hazan et al, 1999; Errico et al, 2002; Evans et al, 2005; Roll-Mecak & Vale, 2005, 2008; Reid & Rugarli, 2010; Fink, 2014).