Publication:

Escobar syndrome is a prenatal myasthenia caused by disruption of the acetylcholine receptor fetal gamma subunit (2006)

Author(s): Hoffmann K; Muller JS; Stricker S; Megarbane A; Rajab A; Lindner TH; Cohen M; Chouery E; Adaimy L; Ghanem I; Delague V; Boltshauser E; Talim B; Horvath R; Robinson PN; Lochmuller H; Hubner C; Mundlos S

    Abstract: Escobar syndrome is a form of arthrogryposis multiplex congenita and features joint contractures, pterygia, and respiratory distress. Similar findings occur in newborns exposed to nicotinergic acetylcholine receptor (AChR) antibodies from myasthenic mothers. We performed linkage studies in families with Escobar syndrome and identified eight mutations within the gamma -subunit gene (CHRNG) of the AChR. Our functional studies show that gamma -subunit mutations prevent the correct localization of the fetal AChR in human embryonic kidney-cell membranes and that the expression pattern in prenatal mice corresponds to the human clinical phenotype. AChRs have five subunits. Two alpha, one beta, and one delta subunit are always present. By switching gamma to epsilon subunits in late fetal development, fetal AChRs are gradually replaced by adult AChRs. Fetal and adult AChRs are essential for neuromuscular signal transduction. In addition, the fetal AChRs seem to be the guide for the primary encounter of axon and muscle. Because of this important function in organogenesis, human mutations in the gamma subunit were thought to be lethal, as they are in gamma -knockout mice. In contrast, many mutations in other subunits have been found to be viable but cause postnatally persisting or beginning myasthenic syndromes. We conclude that Escobar syndrome is an inherited fetal myasthenic disease that also affects neuromuscular organogenesis. Because gamma expression is restricted to early development, patients have no myasthenic symptoms later in life. This is the major difference from mutations in the other AChR subunits and the striking parallel to the symptoms found in neonates with arthrogryposis when maternal AChR auto-antibodies crossed the placenta and caused the transient inactivation of the AChR pathway.

      • Date: 12-05-2006
      • Journal: American Journal of Human Genetics
      • Volume: 79
      • Issue: 2
      • Pages: 303-312
      • Publisher: Cell Press
      • Publication type: Article
      • Bibliographic status: Published

      Keywords: Amino Acid Sequence Animals Arthrogryposis/embryology/genetics/physiopathology Child Female Humans Mice Molecular Sequence Data Myasthenic Syndromes, Congenital/embryology/ genetics/physiopathology Neuromuscular Junction/embryology/genetics/physiopathology Pedigree Pregnancy Protein Subunits/ genetics Receptors, Cholinergic/ genetics

      Staff

      Professor Hanns Lochmuller
      Professor of Experimental Myology