SPTSSA (serine palmitoyltransferase small subunit A) is a regulatory component of the serine palmitoyltransferase (SPT) complex that catalyzes the rate-limiting step in sphingolipid biosynthesis 1. The SPT complex consists of catalytic subunits SPTLC1 and SPTLC2/SPTLC3, with SPTSSA serving as an activating small subunit that stimulates catalytic activity and determines substrate specificity 1. SPTSSA participates in acyl-CoA coordination, with different complex compositions showing distinct substrate preferences - the SPTLC1-SPTLC2-SPTSSA complex favors C16-CoA substrates while SPTLC1-SPTLC3-SPTSSA uses both C14-CoA and C16-CoA 2. The protein is subject to homeostatic regulation by ORMDL proteins that mediate feedback inhibition when sphingolipid levels become excessive 3. Pathogenic variants in SPTSSA cause hereditary spastic paraplegia by impairing ORMDL-mediated negative regulation, leading to excessive sphingolipid synthesis and neurological dysfunction 3. SPTSSA expression is also altered in various cancers, with upregulation associated with poor prognosis in gastric cancer and glioma 45, while decreased expression in renal cell carcinoma correlates with worse outcomes 6. Additionally, SPTSSA expression is affected by viral infections, potentially linking sphingolipid metabolism to immune responses 7.