SYP is a calcium binding integral-membrane glycoprotein, 38 kDa of presynaptic vesicles in all neurons and corresponding vesicles in all neuroendocrine (NE) cells. Moreover SYP is detected in choroid plexus epithelium. Staining is also seen in adrenal cortical cells, goblet cells and Paneth cells, probably due to a closely related protein.
SYP is detected in virtually all neuronal tumours: Neuroblastoma, ganglioneuroblastoma, ganglioneuroma, ganglioglioma, phaeochromocytoma/paraganglioma and central neurocytoma.
SYP may also be detected in other neural crest derived tumours like oligodendroglioma, astrocytoma and ependymoma, however, to a varying extend. Moreover synaptophysin is detected in NE tumours like pancreatic islet tumours, carcinoid and neuroendocrine carcinoma, small cell carcinoma, medullary thyroid carcinoma, and pituitary and parathyroid adenomas. Also adrenal cortical tumours stain for synaptophysin.
SYP is a sensitive marker for the identification of neuronal and NE tumours and NE differentiation. However, it is not as specific as chromogranin A. SYP may also be used for the identification of adrenal cortical tumour.
Colon is recommended as control for detection of SYP. The protocol must be calibrated to give an intense staining reaction of the axons of the Auerbach’s and Meissner’s plexus with a high-level expression of SYP. The endocrine cells of the mucosa and the peripheral nerves situated in lamina propria mucosa must show an at least weak to moderate staining reaction.
Pancreas is also recommended as positive tissue control. Both Langerhans islets and peripheral nerve fibres intermingling between the exocrine cells must be positive.