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The Journal of Neuroscience, February 25, 2009, 29(8):2312-2321; doi:10.1523/JNEUROSCI.2168-08.2009

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Neurobiology of Disease
Congenital Hypomyelinating Neuropathy with Lethal Conduction Failure in Mice Carrying the Egr2 I268N Mutation

Robert H. Baloh,^1,3 Amy Strickland,² Elizabeth Ryu,² Nam Le,² Timothy Fahrner,² Mao Yang,² Rakesh Nagarajan,² and Jeffrey Milbrandt^1,2,3

Departments of ¹Neurology and ²Pathology, and ³Hope Center for Neurological Diseases, Washington University School of Medicine, St. Louis, Missouri 63110

Correspondence should be addressed to either of the following: Dr. Robert H. Baloh, Department of Neurology, Washington University School of Medicine, P.O. Box 8111, 660 South Euclid Avenue, St. Louis, MO 63110, Email: rbaloh{at}wustl.edu; or Dr. Jeffrey Milbrandt, Department of Pathology, Washington University School of Medicine, P.O. Box 8118, 660 South Euclid Avenue, St. Louis, MO 63110, Email: jeff{at}pathology.wustl.edu

Mouse models of human disease are helpful for understanding the pathogenesis of the disorder and ultimately for testing potential therapeutic agents. Here, we describe the engineering and characterization of a mouse carrying the I268N mutation in Egr2, observed in patients with recessively inherited Charcot–Marie–Tooth (CMT) disease type 4E, which is predicted to alter the ability of Egr2 to interact with the Nab transcriptional coregulatory proteins. Mice homozygous for Egr2^I268N develop a congenital hypomyelinating neuropathy similar to their human counterparts. Egr2^I268N is expressed at normal levels in developing nerve but is unable to interact with Nab proteins or to properly activate transcription of target genes critical for proper peripheral myelin development. Interestingly, Egr2^I268N/I268N mutant mice maintain normal weight and have only mild tremor until 2 weeks after birth, at which point they rapidly develop worsening weakness and uniformly die within several days. Nerve electrophysiology revealed conduction block, and neuromuscular junctions showed marked terminal sprouting similar to that seen in animals with pharmacologically induced blockade of action potentials or neuromuscular transmission. These studies describe a unique animal model of CMT, whereby weakness is due to conduction block or neuromuscular junction failure rather than secondary axon loss and demonstrate that the Egr2–Nab complex is critical for proper peripheral nerve myelination.

Key words: myelin; peripheral nerve; axon; neuromuscular junction; nerve; neuropathy

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Received May 13, 2008; revised Dec. 29, 2008; accepted Jan. 11, 2009.

Correspondence should be addressed to either of the following: Dr. Robert H. Baloh, Department of Neurology, Washington University School of Medicine, P.O. Box 8111, 660 South Euclid Avenue, St. Louis, MO 63110, Email: rbaloh{at}wustl.edu; or Dr. Jeffrey Milbrandt, Department of Pathology, Washington University School of Medicine, P.O. Box 8118, 660 South Euclid Avenue, St. Louis, MO 63110, Email: jeff{at}pathology.wustl.edu

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