MID2 and X-linked Opitz G/BBB syndrome: In fact, TRIM18/MID1 is mutated in a developmental disorder characterized by midline defects, X-linked Opitz Syndrome (XLOS, OMIM 300000), and TRIM1/MID2 is responsible for another X-linked form of intellectual disability (MRX101, OMIM 300928) [28,29].