Mobius syndrome

Mobius syndrome (also spelled Moebius) is an extremely rare neurological disorder.

It is named for Paul Julius Möbius.^[1][2]

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Clinical features

Mobius syndrome is caused by abnormal development of the cranial nerves. This rare disorder has a number of causes. Most often affected are the cranial nerves VI and VII. Occasionally the cranial nerves V and VIII are affected.

If the cranial nerve VI is affected, the patient suffers from reduction of lateral gaze. If cranial nerve VII is affected, the patient suffers from bilateral facial palsy — mask-like expressionless face, often with the upper lip retracted due to muscle shrinkage. If cranial VIII is affected the patient suffers from hearing loss.

Although its rarity often leads to late diagnosis, infants with this disorder can be identified at birth: by a "mask-like" expression detectable during crying or laughing due to paresis (palsy) of the sixth and seventh cranial nerves. Other characteristics include:

• abnormalities in the lower appendages, limbs — their fingers may be webbed, shorter than usual or they may have more than 5 toes on their foot
• impaired listening ability
• inability to follow objects with the eye—instead the child turns his or her head to follow
• crossed legs while in fetus
• limitation of heart movement
• exposure keratopathy or corneal erosion
• Hearing loss due to fluid in the ear or nerve loss

Later on, the child may develop speech difficulties, crossed eyes, abnormally small eyes, and fluid building up in the lungs, causing bronchopneumonia. Moebius syndrome has also been linked to increased occurrence of the symptoms of autism.^[3] Some children with Mobius syndrome are mistakenly labelled as mentally retarded, due to their expressionless faces, strabismus, and frequent drooling.

Treatment

There is no single course of medical treatment for Mobius syndrome. Treatment is supportive and in accordance with symptoms. Infants may require feeding tubes or special bottles to maintain sufficient nutrition. Surgery may correct crossed eyes, protect the cornea (via frequent lubrication or tarsorraphy), and improve limb and jaw deformities. Physical and speech therapy can improve motor skills and coordination, and lead to better control of speaking and eating abilities. Nerve and muscle transfers to the corners of the mouth can be performed to provide ability to smile.

Pathological picture

The causes of Mobius syndrome are poorly understood. Many cases have no obvious cause. Others may be genetic.

Some cases are associated with reciprocal translocation between chromosomes or maternal illness. Some maternal trauma may result in impaired or interrupted blood flow (Ischemia) or lack of oxygen (Hypoxia) to a developing fetus. The use of drugs and a traumatic pregnancy may also be linked to the development of Mobius syndrome. The use of the drugs Misoprostol or Thalidomide by women during pregnancy has been linked to the development of Mobius syndrome in some cases.

Some researchers have suggested that the underlying problem of this disorder could be congenital hypoplasia or agenesis of the cranial nerve nuclei. Certain symptoms associated with Mobius syndrome may be caused by incomplete development of facial nerves, other cranial nerves, and other parts of the central nervous system.

In the majority of cases of Mobius syndrome in which autosomal dominant inheritance is suspected, sixth and seventh cranial nerve paralysis (palsy) occurs without associated limb abnormalities.

Oral/dental concerns

Neonatal Period

When a child is born with Moebius Syndrome, there may be difficulty in closing the mouth or swallowing. The tongue may be hypotonic (low muscle tone) or faciculate (quiver). The tongue may be larger or smaller than average. There may be low tone of the muscles of the soft palate, pharynges, and the masticatory system. The palate may be arched excessively (a high palate) since the tongue does not form a suction that would normally shape the palate down further. The palate may have a groove (this may be partially due to intubation early on if it is for an extended period of time) or may be incompletely formed (cleft palate). The opening to the mouth may be small. Feeding problems may become a critical issue early on if adequate nutrition is difficult.

Primary Dentition

The primary (baby) teeth generally start coming in by the first birthday and all 20 teeth may be in by the second birthday. The eruption timing varies greatly. There may be an incomplete formation of the enamel on the teeth called enamel hypoplasia that makes the teeth more vulnerable to caries (cavities). There may be missing teeth eruptions. The lower jaws become more noticeably deficient (micrognathia or retrognathia) if the infant is not closing down properly. The front teeth may not touch when the child closes down because the back teeth have overerrupted. This condition is called an anterior open bite and has facial/skeletal implications. The saliva may be thick or the infant may have a dry mouth.

Transitional Dentition

Between age 5 and 7 most children start losing their primary teeth. Occasionally some primary teeth are slow to exfoliate (fall out) and the dentist may want to remove a primary tooth early to prevent orthodontic problems. Likewise, premature loss of primary teeth may create orthodontic problems later on. Removable or fixed spacers may be needed to prevent the shifting of teeth when a tooth is lost prematurely. Interceptive orthodontic treatment can be initiated at this stage of development to help with crowding or to help relate the upper and lower jaws. Consistent with a high palate is a narrow arch shape of the upper teeth as they line up in the mouth. This may cause the upper front teeth to flare out and become more prone to fracture if accidentally hit. Interceptive orthodontics has an important role in this situation. Appliances that expand the upper arch tend to bring the front teeth back into a more normal position. Some appliances can even help allow the front teeth to close to normal in an open bite situation. The mouth and lips may tend to get dry with the Moebius patient. Lack of a good oral seal (lips together) allows the gingiva (gums) to get dry and may get inflamed and irritated.

Permanent Dentition

After the last primary tooth is lost, usually around age twelve, final orthodontic treatment can be initiated. A patient that has not been able to close or swallow well, probably will have an open bite, deficient lower jaw growth, a narrow archform with crowded teeth and upper anterior flaring of teeth. Orthognathic (jaw) surgery may be indicated. This should be completed in most situations before smile surgery where the Gracilis Muscle is grafted to the face.

References

1. ^ doctor/33 at Who Named It
2. ^ Mobius PJ. Uber angeboren doppelseitige abducens-facialis-lahmung. Munchen Medizinische Wochenschrift. 1888;35:91-4.
3. ^ Gillberg C, Steffenburg S. (1989). "Autistic behaviour in Moebius syndrome"