PSAP (Prosaposin): PSAP is a precursor protein that is processed into saposins, which are essential for the breakdown of lipids within lysosomes. These saposins play a key role in preventing the accumulation of complex lipids in cells. Deficiencies or mutations in PSAP can lead to lysosomal storage disorders, including Gaucher disease, Fabry disease, and metachromatic leukodystrophy.