La myasthénie néonatale transitoire est une complication rare de la myasthénie grave maternelle.
Environ 10 à 15 % des enfants nés de mères possèdent des anticorps anti-récepteur de l'acétylcholine (AChR), et moins fréquemment une kinase spécifique du muscle (MuSK).
Les symptômes apparaissent généralement dès le 3ème jour de vie et, dans presque tous les cas, il existe une parésie faciale bilatérale et des difficultés de succion. Les symptômes disparaissent généralement vers l’âge d’un mois.
Cependant, dans un petit groupe de patients, une maladie beaucoup plus grave peut survenir, avec une arthrogrypose fœtale et une parésie bulbofaciale persistante jusqu'à l'âge adulte, appelée syndrome d'inactivation fœtale de l'AChR, due à des anticorps dirigés contre la sous-unité gamma fœtale, qui est remplacée chez l'adulte par la sous-unité epsilon.
L'inactivation des récepteurs se produit par exposition à des anticorps spécifiques à une période critique du développement.
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Hoffmann K, Müller JS, Stricker S, Megarbane A, Rajab A, Lindner TH et al. Le syndrome d'Escobar est une myasthénie prénatale causée par une perturbation de la sous-unité γ du récepteur fœtal de l'acétylcholine. Le Journal américain de génétique humaine [Internet]. 1er août 2006 [cité le 15 octobre 2022] ;79(2):303–12. Disponible à partir de : https://www.sciencedirect.com/science/article/pii/S0002929707631371