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At a glance

Congenital syndrome characterized by a combination of ☞Moebius Syndrome and ☞Pierre Robin sequence.

Synonyms

Myopathy; Moebius Robin Syndrome.

History

First described in two siblings in 1982 by the American physicians John C. Carey, Robert M. Fineman, and Fred A. Ziter.

Incidence

Unknown, but less than 20 cases have been described. No sexual predilection.

Genetic inheritance

Autosomal recessive. The defect is caused by mutations in the Myomaker gene (MYMK; also known as Transmembrane Protein 8C, TMEM8C), which has been mapped to chromosome 9q34.2. Myomaker is a plasma membrane protein required for the fusion of mononuclear myoblasts to form multinucleate myotubes during muscle development and is also involved in muscle regeneration. The genetic defect results in reduced (not absent) MYMK function.

Pathophysiology

Not completely understood. Electromyography shows fasciculations and small motor units. Nerve conduction velocity and serum creatinine kinase are normal. Muscle biopsy shows a variation in fiber size, evidence of degeneration and regeneration, and a predominance of type II fibers.

Diagnosis

Based on clinical findings of the characteristic facies and muscular weakness. Neuromuscular investigations may confirm the diagnosis.

Clinical aspects

This nonprogressive congenital myopathy is characterized by Moebius sequence (bilateral congenital facial palsy with mild oculomotor palsy), Pierre Robin complex (micro-/retrognathia, high-arched or cleft palate, and glossoptosis), delayed motor milestones, and possible mental delay. Microstomia and micrognathia can be due to partial absence of the mandible. Failure to thrive is very common and multifactorial, as there are potential anatomical and/or neurological problems with absent or difficult swallowing and/or sucking, and gastroesophageal reflux. A gastrostomy tube is often required. Recurrent aspiration pneumonias, often secondary to bulbar palsy, have been described and have resulted in bronchiectases, chronic collapse, and consolidation of lung lobes, occasionally requiring lobectomy. Other facial features may include macro- or microcephaly, prominent forehead, external ophthalmoplegia, ptosis, epicanthal folds, hypertelorism, downward slanting of the palpebral fissures, low-set and posteriorly rotated ears, flat nasal root, upturned nose with anteverted nares, long philtrum, thin upper lip, and absent or hypoplastic tongue (in about half of the patients). In approximately two-thirds of patients, the pectoral muscles are absent or hypoplastic (☞Poland Syndrome) and ulnar deviation of the hand may be present. Abnormal palmar creases may be present. MRI- or CT-scanning of the brain may be normal or occasionally reveal bilateral ventriculomegaly, subependymal heterotopia, thinning of the white matter, small areas of necrosis with microcalcifications, or hypoplastic pons, and brainstem with enlarged prepontine and pontocerebellar cisterns. Muscle weakness is secondary to a nonspecific primary myopathy with mild axial and appendicular weakness. Facial weakness resulting in an expressionless (amimic) face is common. Muscle biopsies can reveal fatty infiltrations and variable fiber size with a high number of ...

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