MID1 and X-linked Opitz G/BBB syndrome: MID1 is mutated in X-linked Opitz G/BBB syndrome, a rare genetic disorder that results in malformations along the midline of the body, including hypertelorism, hypospadias, and laryngo-tracheo-esophageal defects (Baldini et al., 2020, Trockenbacher et al., 2001).