Opitz G/BBB syndrome (OS) is a multiple congenital anomalies disorder characterized by malformations of the midline including hypertelorism, laryngo-tracheo-esophalgeal defects and hypospadias. There are two clinically indistinguishable genetic subtypes of Opitz G/BBB: X-linked Opitz G/BBB syndrome (XLOS), and autosomal dominant Opitz G/BBB syndrome (ADOS) (see these terms).