Serine palmitoyltransferase, which consists of two different subunits, is the key enzyme in sphingolipid biosynthesis. It converts L-serine and palmitoyl-CoA to 3-oxosphinganine with pyridoxal 5'-phosphate as a cofactor. SPT1 is the long chain base subunit 1 of mammalian serine palmitoyltransferase. SPT1 is not catalytically active but is necessary for the stabilization of the SPT2 subunit and anchoring the holoenzyme to the cytosolic face of the endoplasmic reticulum. Missense mutations in this gene have been identified in patients with hereditary sensory neuropathy type 1 (HSAN1). These mutations induce a shift in the substrate specificity of the holoenzyme, leading to the formation and accumulation of two neurotoxic sphingolipids.