Recently, several HSP proteins, including atlastin-1 (SPG3A), spastin (SPG4), seipin (SPG17), spartin (SPG20), and REEP1 (SPG31)—which together are mutated in over 50% of HSP patients –regulate the size and/or number of lipid droplets (LDs) in HEK293, COS7, and HeLa cells in vitro, as well as in fat bodies of worms and flies in vivo [14, 15, 19, 30, 51, 65]. This evidence concerns the gene SPAST and hereditary spastic paraplegia.