The analysis of CSF and blood plasma in HSP patients with CYP7B1 gene mutation defined alterations in levels of several oxysterols including the accumulation of metabolic precursor substrates (25-OH and 27-OH), indicative of altered flux through the classical versus alternate arms (Abdel-Khalik et al., 2018; Marelli et al., 2018; Kakiyama et al., 2019). This evidence concerns the gene CYP7B1 and hereditary spastic paraplegia.