TFG and hereditary spastic paraplegia: Although studies using homozygous mutant p.Arg106Cys TFG cells are of great value not only for elucidating the pathogenesis of HSP but also for studying the consequences of the loss of functional TFG, the knowledge obtained from TFG-knockout (KO) mouse models is necessary for understanding the physiological functions of TFG and neurodegenerative disorders caused by mutations affecting this gene.