Synaptic vesicle phosphoprotein that enhances spontaneous neurotransmitter release but does not effect induced neurotransmitter release (By similarity). Unlike other synaptotagmins, it does not bind Ca(2+) or phospholipids (By similarity). Essential for mossy-fiber long-term potentiation in the hippocampus (By similarity). . This is the function of SYT12 (synaptotagmin 12, Ensembl gene identifier ENSG00000173227).