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Six patients with a newly described genetic syndrome in Iraqi and Iranian Jews of congenital myasthenia associated with facial malformations were studied with voluntary and stimulation single fiber EMG (SFEMG). Voluntary SFEMG revealed abnormal jitter in all patients in both extensor digitorum communis (EDC) and orbicularis oculi (OOC) muscles, though much smaller in the clinically unaffected EDC. SFEMG study of OOC muscle by axonal stimulation at rates from 1 to 48 Hz showed the most increased jitter at the highest stimulation frequencies in the majority of end-plates, one-third of which showed maximal jitter at intermediate rates. These results may suggest a postsynaptic abnormality as the underlying cause for the neuromuscular transmission defect, and demonstrate the usefulness of SFEMG in the diagnosis of congenital myasthenia.

Fourteen Jewish patients from 10 families of either Iraqi or Iranian origin with congenital myasthenia had associated facial malformations which included an elongated face, mandibular prognathism with class III malocclusion and a high-arched palate. Other common features were muscle weakness restricted predominantly to ptosis, weakness of facial and masticatory muscles, and fatigable speech; mild and nonprogressive course; response to cholinesterase inhibitors; absence of antibodies to acetylcholine receptor; decremental response on repetitive stimulation at 3 Hz but no repetitive compound muscle action potential in response to a single nerve stimulus. This newly recognized form of congenital myasthenia with distinctive ethnic clustering and associated facial malformations is transmitted as an autosomal recessive disorder. The facial abnormalities may be secondary to the neuromuscular defect or may be primary and unrelated. Further studies are needed to elucidate the defect in neuromuscular transmission responsible for the pathogenesis of this syndrome.