Definition:

Moebius syndrome (MBS) is a complex, rare developmental anomaly of the hindbrain, that has been described as the combination of congenital palsies of the facial and abducens cranial nerves. Other cranial neuropathies can also be found, most notably cranial nerves V, IX, X, and XII. The disorder presents with varying phenotype and severity. Frequently, it has additional features including orofacial malformations, limb defects, and musculoskeletal, behavioral, and cognitive abnormalities. The specific etiology of MBS is unknown, and theories of the underlying pathophysiology and genetics are numerous. The two main theories underlying the pathogenesis of MBS are an embryological developmental defect in the rhombomere segments including the facial nerve nuclei and an interruption of the vascular supply resulting in ischemia. It has also been reported that mutations in the MBS1, MBS2, and MBS3 gene loci all have contributed to the development of MBS through various pathways. HOX family genes coding for homeobox domains, also, have been implicated in the abnormal development of the human brain.