What is the cause of Moebius syndrome?

The cause of Moebius syndrome is not well understood. Genetic research into the condition has not shown a clear genetic pattern.

There is no family history of Moebius syndrome and it occurs sporadically. There are some conditions with overlapping features to Moebius syndrome that may run in families, but in studies supported by the Moebius Syndrome Foundation, no individuals with classic Moebius syndrome have more than one affected family member in their families.

While some research completed in Europe, with lead authors from the Netherlands, has indicated that Moebius syndrome may occur with changes in genes PLXND1 and REV3L, researchers in the United States have been unable to identify additional patients with changes in these two genes.

Moebius syndrome-like conditions may occur from fetal exposure to drugs that cause the constriction of blood vessels. However, it is important to understand that these drugs cause a minority of cases of Moebius syndrome. 

Some medical literature has theorized that reduced blood flow, or vascular interruption, may contribute or be the cause of Moebius syndrome.

Research into the cause of Moebius syndrome is ongoing.

How Is Moebius Syndrome Diagnosed?

Moebius syndrome is primarily a clinical diagnosis, meaning it is identified based on a medical professional’s evaluation of a patient’s symptoms and physical examination, rather than a single definitive laboratory test.

The core diagnostic criteria require the presence of both:

•   Congenital (present-at-birth) facial weakness affecting one or both sides of the face (cranial nerve 7)
•   Inability to move one or both eyes outward horizontally (cranial nerve 6 / abducens nerve)

A neurologist, geneticist, or craniofacial specialist typically leads the evaluation. The diagnostic workup may include:

•   Neurological examination to assess cranial nerve function

•   MRI or CT brain imaging to evaluate brainstem structure and look for hypoplasia (underdevelopment) of relevant cranial nerve nuclei

•   Ophthalmological assessment to document eye movement range

•   Genetic testing to rule out overlapping conditions

•   Hearing evaluation, as some individuals have associated hearing loss

• Feeding and swallowing assessment, particularly in infants

While there is no cure for Moebius syndrome, many effective treatments and therapies can significantly improve quality of life. Management is typically individualized and multidisciplinary, meaning a team of specialists works together to address each person’s specific needs.

When Is Moebius Syndrome Typically Identified?

In many cases, Moebius syndrome is recognized at birth or within the first weeks of life. Parents and newborn care providers may notice:

Difficulty feeding or latching (due to limited lip movement and facial muscle weakness)

•   An absent or reduced smile and limited facial expression
•   Eyes that do not track side-to-side or appear misaligned
•   A weak or reduced cry in some infants

In milder presentations, the diagnosis may come later in infancy or childhood, sometimes prompted by speech delays, eye alignment concerns (strabismus), or a referral from a pediatrician who notices asymmetric facial movement.

How is Moebius syndrome treated and managed?

Treatment approaches vary depending on which cranial nerves are affected and the severity of presentation. Common areas of intervention include:

Speech & Feeding Therapy: Many infants with Moebius syndrome have difficulty feeding due to reduced lip seal and facial muscle tone. Speech-language pathologists (SLPs) work with families from early infancy to support safe feeding, and later assist with speech articulation, which can be affected by limited lip and tongue movement.

 Physical & Occupational Therapy: For individuals with low muscle tone (hypotonia), limb differences, or club foot, physical and occupational therapy support motor development, strength, coordination, and daily function.

 Eye Care: Because many individuals with Moebius syndrome cannot fully close their eyes or blink normally, protecting eye health is critical. This may involve lubricating eye drops, moisture chamber glasses, patching for amblyopia (lazy eye), and surgical intervention for strabismus (crossed eyes).

 Dental Care: Reduced oral muscle tone, smaller jaws, and mouth-breathing can affect dental development. Regular dental monitoring and early orthodontic evaluation are recommended.

Smile Surgery (Gracilis Muscle Transfer): Some individuals with Moebius syndrome choose to undergo a surgical procedure called a gracilis free muscle transfer, in which a small muscle from the inner thigh is transplanted to the face to enable a smile. This is an elective procedure, typically performed in childhood or adulthood, and results vary. It is not appropriate for everyone and is a deeply personal decision.

Hearing Supports: For individuals with associated hearing loss, audiological evaluation and hearing aids or other assistive devices may be recommended.

The estimated incidence of Moebius syndrome is roughly 2 to 20 cases per 1 million births. Moebius syndrome occurs equally in all populations. The condition occurs in all ethnicities. There is no gender bias; males and females are affected equally.

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