ENO2 and Nijmegen breakage syndrome: Neuron-specific enolase (NSE) is an isoform of the glycolytic enzyme enolase specific to neural tissues, and is found in high levels in the serum in different endocrine tumors like carcinoids, medullary thyroid carcinoma, pituitary adenomas, islet cell tumors, small-cell lung carcinoma, malignant pheochromocytoma, ganglioneuromas, schwannomas and NBs (126–132).