Semaphorins are a family of cell surface and secreted proteins involved in neural development that are conserved from insects to humans. Members of this family are approximately 750 amino acids in length (including signal sequences) and are defined by a conserved extracellular a?semaphorina? domain of approximately 500 amino acids containing 14-16 cysteines, blocks of conserved sequences and no obvious repeats. The transmembrane semaphorins are characterized by an additional 80 amino acid transmembrane domain and an 80-110 amino acid cytoplasmic domain. Secreted and cell-bound semaphorins chemically attract and repel the growth of neural axons, guiding the development of intricate networks of neural tissue. SEMA3E is a secreted semaphorin with 775 amino acids. Mutations in the SEMA3E gene are associated with CHARGE syndrome, a disorder characterized by cranial nerve dysfunction, coloboma of the eye, choanal atresia, inner and external ear abnormalities, cardiac anomalies, genitourinary abnormalities, and growth retardation.