Highly fatal fast-channel syndrome caused by AChR epsilon subunit mutation at the agonist binding site.
Article Details
- CitationCopy to clipboard
Shen XM, Brengman JM, Edvardson S, Sine SM, Engel AG
Highly fatal fast-channel syndrome caused by AChR epsilon subunit mutation at the agonist binding site.
Neurology. 2012 Jul 31;79(5):449-54. doi: 10.1212/WNL.0b013e31825b5bda. Epub 2012 May 16.
- PubMed ID
- 22592360 [ View in PubMed]
- Abstract
OBJECTIVE: To characterize the molecular basis of a novel fast-channel congenital myasthenic syndrome. METHODS: We used the candidate gene approach to identify the pathogenic mutation in the acetylcholine receptor (AChR) epsilon subunit, genetically engineered the mutant AChR into HEK cells, and evaluated the level of expression and kinetic properties of the mutant receptor. RESULTS: An 8-year-old boy born to consanguineous parents had severe myasthenic symptoms since birth. He is wheelchair bound and pyridostigmine therapy enables him to take only a few steps. Three similarly affected siblings died in infancy. He carries a homozygous p.W55R mutation at the alpha/epsilon subunit interface of the AChR agonist binding site. The mutant protein expresses well in HEK cells. Patch-clamp analysis of the mutant receptor expressed in HEK cells reveals 30-fold reduced apparent agonist affinity, 75-fold reduced apparent gating efficiency, and strikingly attenuated channel opening probability (P(open)) over a range agonist concentrations. CONCLUSION: Introduction of a cationic Arg into the anionic environment of alpha/epsilon AChR binding site hinders stabilization of cationic ACh by aromatic residues and accounts for the markedly perturbed kinetic properties of the receptor. The very low P(open) explains the poor response to pyridostigmine and the high fatality of the disease.