Identification of an agrin mutation that causes congenital myasthenia and affects synapse function.
We report the case of a congenital myasthenic syndrome due to a mutation in AGRN, the gene encoding agrin, an extracellular matrix molecule released by the nerve and critical for formation of the neuromuscular junction. Gene analysis identified a homozygous missense mutation, c.5125G>C, leading to the p.Gly1709Arg variant. The muscle-biopsy specimen showed a major disorganization of the neuromuscular junction, including changes in the nerve-terminal cytoskeleton and fragmentation of the synaptic gutters. Experiments performed in nonmuscle cells or in cultured C2C12 myotubes and using recombinant mini-agrin for the mutated and the wild-type forms showed that the mutated form did not impair the activation of MuSK or change the total number of induced acetylcholine receptor aggregates. A solid-phase assay using the dystrophin glycoprotein complex showed that the mutation did not affect the binding of agrin to alpha-dystroglycan. Injection of wild-type or mutated agrin into rat soleus muscle induced the formation of nonsynaptic acetylcholine receptor clusters, but the mutant protein specifically destabilized the endogenous neuromuscular junctions. Importantly, the changes observed in rat muscle injected with mutant agrin recapitulated the pre- and post-synaptic modifications observed in the patient. These results indicate that the mutation does not interfere with the ability of agrin to induce postsynaptic structures but that it dramatically perturbs the maintenance of the neuromuscular junction.
Huzé
Caroline
C
Equipe Différenciation Neuromusculaire, UMR 5239, Ecole Normale Supérieure Lyon, CNRS, Université Lyon 1, Lyon, France.
Bauché
Stéphanie
S
Richard
Pascale
P
Chevessier
Frédéric
F
Goillot
Evelyne
E
Gaudon
Karen
K
Ben Ammar
Asma
A
Chaboud
Annie
A
Grosjean
Isabelle
I
Lecuyer
Heba-Aude
HA
Bernard
Véronique
V
Rouche
Andrée
A
Alexandri
Nektaria
N
Kuntzer
Thierry
T
Fardeau
Michel
M
Fournier
Emmanuel
E
Brancaccio
Andrea
A
Rüegg
Markus A
MA
Koenig
Jeanine
J
Eymard
Bruno
B
Schaeffer
Laurent
L
Hantaï
Daniel
D
D000328:Adult; D018171:Agrin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001706:Biopsy; D002460:Cell Line; D004252:DNA Mutational Analysis; D049030:Dystroglycans / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008956:Models, Chemical; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology / Q000601:surgery / Q000648:ultrastructure; D020125:Mutation, Missense; D020294:Myasthenic Syndromes, Congenital / Q000235:genetics*; D009469:Neuromuscular Junction / Q000235:genetics / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D010375:Pedigree; D017434:Protein Structure, Tertiary; D051381:Rats; D011950:Receptors, Cholinergic / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013569:Synapses / Q000378:metabolism*
D018171:Agrin; D011950:Receptors, Cholinergic; D011994:Recombinant Proteins; D049030:Dystroglycans