FBXL5 and movement disorder: Lastly, target gene searches for another movement disorder called Hereditary spastic paraplegia (HSP) resulted in identification of a disease gene at the 4p16-p15 locus (SPG 38, [36]), which is near a new E3 ubiquitin ligase called F-box and leucine-rich repeat protein 5 (FBXL5, 4p15.32).