SPG11 and hereditary spastic paraplegia: This was observed with KIF1A (SPG30), in which missense homozygous mutations located in the kinesin motor domain account for a relatively pure HSP (Erlich et al. 2011; Klebe et al. 2012b), whereas heterozygous mutations located in the ATP binding site of KIF1A were found in patients with severe mental retardation with axial hypotonia, peripheral spasticity and mild atrophy of cerebellum and or corpus callosum, a phenotype reminiscent of SPG11 (Hamdan et al. 2011; Chang et al. 2014).