Moebius syndrome (MBS)

What is Moebius syndrome (MBS)?

Moebius Syndrome is a rare neurological condition which presents with the lack of, or severe underdevelopment of the 6th and 7th cranial nerves.

As a congenital condition it is most commonly diagnosed at birth.

This underdevelopment in turn causes congenital facial palsy and abnormal ocular or eye movements. Affected individuals have less control over their facial expressions and eye movements.

Syndrome Synonyms:
Facial diplegia - congenital Mobius Syndrome; Mbs Moebius Sequence Moebius syndrome (congenital facial diplegia)

What gene changes cause Moebius syndrome (MBS)?

There is currently no common genetic cause identified as responsible for causing the syndrome. It is currently believed to be caused by a mixture of genetic and environmental factors, but what these are exactly remains to be identified.

What are the main symptoms of Moebius syndrome (MBS)?

The syndrome affects the 6th and 7th cranial nerves which are responsible for eye movement and the controlling and making of facial expressions. This leads to syndromes such as crossed eyes, and further issues with speaking, earring, hearting and the ability to form facial expressions.

Other health conditions associated with the syndrome include a cleft palate, hearing problems, club foot, missing or fused fingers, Poland’s syndrome which affects the chest and upper limbs, dental problems and motor delay.

Possible clinical traits/features:
Autosomal dominant inheritance, Syndactyly, Pes planus, Open mouth, Ophthalmoparesis, Short neck, Poor coordination, Strabismus, Talipes, Talipes equinovarus, Radial deviation of finger, Reduced number of teeth, Camptodactyly, Respiratory difficulties, Sporadic, Phenotypic variability, Ptosis, Clinodactyly, Clumsiness, Clinodactyly of the 5th finger, Congenital fibrosis of extraocular muscles, Brachydactyly, Dysdiadochokinesis, Dysarthria, Dysphagia, Motor delay, Decreased testicular size, Exotropia, Feeding difficulties in infancy, Finger syndactyly, Facial diplegia, Arthrogryposis multiplex congenita, Split hand, Epicanthus, Everted lower lip vermilion, Esotropia, Opacification of the corneal stroma, Hearing impairment, Depressed nasal bridge, Gait disturbance, Hand clenching, High palate, Short phalanx of finger, Delayed speech and language development, Visual impairment, Hypertelorism, Hypoplasia of the brainstem, Hypogonadotropic hypogonadism, Lower limb undergrowth, Muscular hypotonia, Micropenis, Micro

How does someone get tested for Moebius syndrome (MBS)?

The initial testing for Moebius syndrome can begin with facial analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the need for further testing. A consultation with a genetic counselor and then a geneticist will follow. 

Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.   

Medical information on Moebius syndrome

Facial and abducens palsies at birth is a hallmark of this syndrome, while micrognathia, limb defects, hearing loss, intellectual disability and autism may also be present. Most cases are sporadic, but a small percentage are reported to run in families.

The essential features of Moebius syndrome are unilateral or bilateral facial and abducens palsies. Other cranial nerve palsies, particularly bulbar, may be present. Associated facial features include micrognathia, epicanthic folds, structural abnormalities of the ears, and defective branchial musculature. Limb defects, present in some cases, include syndactyly, polydactyly, brachydactyly, oligodactyly and absent trapezoid or pectoral muscles.

Baraitser (1977) pointed out that in the absence of limb abnormalities diagnosis can be difficult, and cases with the limb deformity have a low recurrence risk. MacDermot et al., (1991) make the same point and review the literature of familial recurrence of the ""Moebius spectrum"" (ie: facial weakness but without limb abnormalities).

There is considerable overlap with Poland syndrome and the hypoglossia-hypodactyly syndrome. Larrandaburu et al., (1999) reported a family where a 14-year-old girl had the combination of Poland and Moebius syndrome, whereas the maternal aunt had features of Moebius syndrome.

Bouwes Bavinck and Weaver (1986) and St Charles et al., (1993) reviewed the evidence for a vascular etiology for these conditions. Hennekam (1990) reported a family where one individual had a Poland anomaly, another a hemifacial microsomia and another a neural tube defect. A vascular etiology was suggested.

In support of this hypothesis, Lipson et al., (1996) reported two infants. One had ""classical Moebius syndrome,"" although without hand abnormalities, and the other had hypertonic cerebral palsy and at postmortem was shown to have hypoxic/ishaemic lesions to the caudate nucleus, putamen and striatum. In both cases, the mothers had trauma during pregnancy at 18 and 14 weeks gestation, respectively, resulting in rupture of the spleen and severe hypotension.

Lammens et al., (1998) reported two severe cases who both died in the neonatal period. One had joint contractures of the upper and lower limbs and was found to have spleno-gonadal fusion. The other had peromelia. In both, brain stem abnormalities and tegmental microccalcifications were observed. Matsunaga et al., (1998) reported another severe case with calcification in the floor of the fourth ventricle.

Verzijl et al., (2003) classify Moebius syndrome as a condition of rhombencephalic maldevelopment, to include Duane retraction syndrome (34%), a conjugated horizontal gaze palsy (48%), congenital fibrosis of the extraocular muscles (9%) at the top of the brain stem and lingual involvement (77%), dysfunction of the palate and pharynx (56%), respiratory problems, incoordination and other features thought to originate in the lower brain stem.

A case that followed the ingestion of ergotamine (causing vasoconstriction and uterine contractions) was reported by Graf and Shepard, (1997) and another by Smets et al., (2004).

Another 10 cases with Moebius syndrome and delayed development were reported by Wolff and Koutsandreou (2001). A severe case (with brain stem calcification) in an infant whose mother took cocaine during pregnancy was reported by Puvabanditsin et al., (2005).

Intellectual disability can be variable, but Baraitser (1977) noted significant disability in 50% of carefully diagnosed cases. Briegel (2006) reviewed the development and behavior in Moebius syndrome and concluded that 10-15% of cases were delayed. Autism is occurring more frequently.

Five of the six patients reported by Dooley et al., (2004) had brain stem calcification. Absence of the middle cerebellar peduncles occurred in the case reported by Ouanounou et al., (2005). Hydrosyringomyelia has also been reported (Losito et al., 2013).

Sjogreen et al., (2001) discuss the management of the condition.

A family (without limb defects and total ophthalmoplegia) was reported by Dumars et al., (2008). Note, however, the affected mother and child reported by Graziadio et al., (2010). The child had coxa vara, club feet, small toes, hypoplastic nails, and restriction at hips and knees; the mother had coxa valga and club feet. Both had facial palsies.

Ziter et al., (1977) reported a dominant family where seven individuals in three generations had congenital facial diplegia with finger contractures. All affected individuals had an apparently balanced chromosome translocation (1p34;13q13).

Slee et al., (1991) reported a female infant with features of Moebius syndrome associated with a 13q12.2 deletion. The mother's chromosomes were normal, but the father had died. There were no abnormalities of the extremities.

Kremer et al., (1996) localized the gene to 3q21-25 in a large family originally reported by van der Wiel et al., (1957) where there were features of Moebius syndrome, albeit only facial palsies. In a neuropathological study on members of this family, Verzijl et al., (2005) concluded that the pathology differed from that seen in Moebius syndrome, in that the only pathology was a significant reduction of the facial nerve motor neurons.

Nishikawa et al., (1997) reported a male infant with facial diplegia who had a de novo reciprocal translocation (46,XY,t(1;2)(p22.3;q21.1)).

Verzijl et al., (1999) reported a dominant pedigree where affected individuals had unilateral or bilateral facial weakness. Sensorineural hearing loss also appeared to be part of the condition. The gene was mapped to 10q21-22. The family was previously described by Fortanier and Speijer (1935) and Nicolai et al., (1986). See also Becker Christensen et al., (1974) for a possible dominant family with some features.

Whole-exome sequencing revealed a de novo heterozygous missense mutation in TUBB3 in only one individual with atypical Moebius syndrome, who had a near-complete ophthalmoplegia, agenesis of the corpus callosum, and absence of the septum pellucidum. No limb abnormalities were observed.

Tomas-Roca et al., (2015) reported de novo heterozygous mutations in PLXND1 and REV3L genes in six unrelated patients with Moebius syndrome. The clinical features were highly variable. While clinical presentation in some patients was consistent with the clinical criteria for Moebius syndrome, some patients only had bilateral facial paralysis and no weakness of the abducens nerves, suggestive of the restricted hereditary congenital facial palsy phenotype.

Patel et al., (2017) described three females and six males with Moebius syndrome. Clinical characteristics of this cohort included unilateral or bilateral facial and abducens nerve palsy, feeding difficulties, limb malformations (lower extremity truncating defects, oligodactyly, syndactyly, and talipes equinovarus), intellectual disability, tongue abnormalities (hypoplasia or ankyloglossia), short stature, and Poland anomaly.

* This information is courtesy of the L M D.
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