Human Molecular Genetics, Vol 6, 767-774, Copyright © 1997 by Oxford University Press
R Croxen, C Newland, D Beeson, H Oosterhuis, G Chauplannaz, A Vincent and J Newsom- Davis
Congenital myasthenic syndromes are a group of rare genetic disorders that
compromise neuromuscular transmission. A subset of these disorders, the
slow-channel congenital myasthenic syndrome (SCCMS), is dominantly
inherited and has been shown to involve mutations within the muscle
acetylcholine receptor (AChR). We have identified three new SCCMS mutations
and a further familial case of the alpha G153S mutation. Single channel
recordings from wild-type and mutant human AChR expressed in Xenopus
oocytes demonstrate that each mutation prolongs channel activation
episodes. The novel mutations alpha V156M, alpha T254I and alpha S269I are
in different functional domains of the AChR alpha subunit. Whereas alpha
T254I is in the pore-lining region, like five of six previously reported
SCCMS mutations, alpha S269I and alpha V156M are in extracellular domains.
alpha S269I lies within the short extracellular sequence between M2 and M3,
and identifies a new region of muscle AChR involved in ACh binding/channel
gating. alpha V156M, although located close to alpha G153S which has been
shown to increase ACh binding affinity, appears to alter channel function
through a different molecular mechanism. Our results demonstrate
heterogeneity in the SCCMS, indicate new regions of the AChR involved in
ACh binding/channel gating and highlight the potential role of mutations
outside the pore-lining regions in altering channel function in other ion
channel disorders.
ARTICLES
Mutations in different functional domains of the human muscle acetylcholine receptor alpha subunit in patients with the slow-channel congenital myasthenic syndrome
Neurosciences Group, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK.
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