CYP7B1 and hereditary spastic paraplegia: Mutations in CYP7B1 were initially defined in patients with an early onset, autosomal recessive form of pure HSP (SPG5) (Tsaousidou et al., 2008); however, more clinically complex forms of HSP (including spastic ataxia and white matter lesions, demyelinating polyneuropathy, optic atrophy, and familial macular dystrophy) have subsequently been infrequently described (Tsaousidou et al., 2008; Arnoldi et al., 2012; Schöls et al., 2017; Marelli et al., 2018).