Mobius syndrome is a very rare congenital disorder characterized by palsies of various cranial nerves, most commonly of the facial and abducens nerves. Main symptoms, developing as early as infancy and during the neonatal period, are incomplete lip closure, poor facial expression, and a fixed eye gaze, together with facial and limb abnormalities. The diagnosis primarily rests on clinical criteria, as the exact etiology of Mobius syndrome remains unknown. Familial cases have been described.
Mobius syndrome (MS) is considered to be a rare disorder in clinical practice, with estimated incidence rates of 1 in 250,000 births . The exact cause of this syndrome, as well as its pathogenesis, remain unknown, with current hypotheses involving genetic mutations and pathological events during embryogenesis    . Although familial cases exist, most cases develop Mobius syndrome sporadically and the clinical presentation may be visible from neonatal period  . The most important features of MS are palsies of the facial (VII) and abducens (VI) cranial nerves  . Reduced facial mimicry (expression during smiling and crying are particularly affected) appearing either in a unilateral or bilateral fashion, and feeding difficulties due to incomplete lip closure that impairs sucking are main signs of facial nerve palsy  . Conversely, abducens nerve palsy is associated with a range of ocular abnormalities, as palsies of other cranial nerves responsible for innervating the ocular muscles (the oculomotor and the trochlear, or III and IV, respectively)  . Commonly reported findings are a fixed gaze, strabismus (either convergent or divergent), defects in abduction/adduction, and ptosis   . Additionally, hypoplasia of the tongue (hypoglossal nerve palsy), speech difficulties, and impaired swallowing (stemming from trigeminal, glossopharyngeal and/or vagus nerve palsies) are also reported in many patients  . Furthermore, cranial nerve palsies are accompanied by anatomical changes of the face (micrognathia, microphthalmia, smaller ears, a bifid uvula) and the musculoskeletal system (torticollis, syndactyly, brachydactyly, clubfoot, and muscular agenesis, particularly of the chest wall)    . Finally, studies identified autism and mental retardation in up to a third of cases .
Because of the rare occurrence of Mobius syndrome, the diagnosis may be difficult to make, especially in cases with milder phenotypes. For this reason, a detailed history that will assess the main symptoms, as well as their onset and severity (the parents are often the most reliable source, as young children are the main patient population) must be obtained. The physical examination, however, which allows the physician to identify signs of cranial nerve palsies and facial/musculoskeletal abnormalities, is the critical part of the diagnostic workup. A complete inspection of the body and a comprehensive neurological workup are key components. MS remains a diagnosis on clinical grounds, but imaging studies of the brain, such as magnetic resonance imaging (MRI), can provide additional clues by detecting hypoplasia of cranial nerves, their nuclei and their branches  . Calcifications of the brainstem have also been reported on computed tomography (CT) by isolated studies . Despite the fact that certain genetic mutations have been revealed in patients with MS   , specific genetic tests are yet to be designed.