Plays a role in phosphate homeostasis. Mediates phosphate export from the cell (PubMed:23791524, PubMed:25938945). Binds inositol hexakisphosphate (Ins6P) and similar inositol polyphosphates, such as 5-diphospho-inositol pentakisphosphate (5-InsP7); these are important intracellular signaling molecules (PubMed:27080106). Widely expressed. Detected in spleen, lymph node, thymus, leukocytes, bone marrow, heart, kidney, pancreas and skeletal muscle. Expressed in fetal liver. The SPX domain has high affinity for inositol polyphosphates, such as myo-inositol hexakisphosphate and 5-diphospho-myo-inositol pentakisphosphate (5-InsP7). Its affinity for inorganic phosphate is tow to three orders of magnitude lower. The disease is caused by variants affecting the gene represented in this entry. Belongs to the SYG1 (TC 2.A.94) family. It is unclear whether its ability to act as a receptor for xenotropic and polytropic murine leukemia retroviruses is relevant in vivo and whether such viruses can infect human.