What is Moebius syndrome?

Varying definitions of Moebius syndrome exist in the medical literature. To improve consistency in diagnosis, clinical criteria for a diagnosis of Moebius syndrome were established by an international group of experts at a Moebius Syndrome Foundation research conference in 2007. 

These two strict clinical criteria are:

1) Congenital (occurring from birth), non-progressive congenital facial weakness

2) Inability to abduct (move the eye away from the nose) one or both eyes

Both criteria must be present for a diagnosis of Moebius syndrome. These two symptoms may be due to impairment in the facial nerve (cranial nerve 7) and the abducens nerve (cranial nerve 6), respectively.

In addition to the above strict clinical criteria, additional signs or symptoms may also be present, including, but not limited to:

• Other cranial nerve involvement
• Strabismus (misalignment of the eyes)
• Hearing loss
• Club foot
• Limb reduction deficits
• Other limb anomalies
• Poland anomaly
• Muscular hypotonia
• Congenital heart disease
• Developmental delay/ intellectual disability
• Autism

Moebius syndrome was originally described by German ophthalmologist Alfred Graefe in 1880, but is named for German neurologist Paul Julius Moebius, who reported features of this condition in 1888.

The incidence of Moebius syndrome is roughly 2 to 20 cases per million births. The condition occurs in all ethnicities. There is no gender bias (males and females are affected equally). At present, the etiology of Moebius syndrome is currently poorly understood, but may be due to genetic and/or environmental factors.

In very rare cases, a change in specific genes may be causative of Moebius syndrome.  Additionally, there are several other separate conditions with similarities to Moebius syndrome that have identified genetic etiologies.

References:
1 Miller, G. (2007). Neurological disorders. The mystery of the missing smile.
Science 316, 826–827.
2 Webb, BD, Shabaan S, Gaspar H, et al. (2012). HOXB1 founder mutations in
humans recapitulate the phenotype of Hoxb1-/- mice. Am J Hum Genet 91, 171-
179.
3 Tomas-Roca L, Tsaalbi-Shtylik A, Jansen JG, et al. (2015). De novo mutations
in PLXND1 and REV3L cause Moebius syndrome. Nat Commun 6:7199, 1-9.

Read more information on the Twelve_Cranial_Nerves.