Endothelin-converting enzyme 1, also known as ECE-1, is a single-pass type I I membrane protein which belongs to the peptidase M13 family. ECE-1 converts big endothelin-1 to endothelin-1. ECE-1 is a membrane metalloprotease that generates endothelin from its direct precursor big endothelin. Four isoforms of ECE-1 are produced from a single gene through the use of alternate promoters. These isoforms share the same extracellular catalytic domain and contain unique cytosolic tails, which results in their specific subcellular targeting.All isoforms of ECE-1 are expressed in umbilical vein endothelial cells, polynuclear neutrophils, fibroblasts, atrium cardiomyocytes and ventricles. Isoforms A, B and C of ECE-1 are also expressed in placenta, lung, heart, adrenal gland and phaeochromocytoma; isoforms A and C of ECE-1 in liver, testis and small intestine; isoform B, C and D of ECE-1 in endothelial cells and umbilical vein smooth muscle cells; isoforms C and D in saphenous vein cells, and isoform C in kidney. Defects in ECE1 are a cause of Hirschsprung disease, cardiac defects and autonomic dysfunction. It is a form of Hirschsprung disease with skip-lesions defects, craniofacial abnormalities and other dysmorphic features, and autonomic dysfunction.