A novel missense mutation of CMT2P alters transcription machinery.
Charcot-Marie-Tooth type 2P (CMT2P) has been associated with frameshift mutations in the RING domain of LRSAM1 (an E3 ligase). This study describes families with a novel missense mutation of LRSAM1 gene and explores pathogenic mechanisms of CMT2P.



Patients with CMT2P were characterized clinically, electrophysiologically, and genetically. A neuronal model with the LRSAM1 mutation was created using CRISPR/Cas9 technology. The neuronal cell line along with fibroblasts isolated from the patients was used to study RNA-binding proteins.



This American family with dominantly inherited axonal polyneuropathy reveals a phenotype similar to those in previously reported non-US families. The affected members in our family cosegregated with a novel missense mutation Cys694Arg that alters a highly conserved cysteine in the RING domain. This mutation leads to axonal degeneration in the in vitro neuronal cell line. Moreover, using protein mass spectrometry, we identified a group of RNA-binding proteins (including FUS, a protein critically involved in motor neuron degeneration) that interacted with LRSAM1. The interactions were disrupted by the Cys694Arg mutation, which resulted in reduction of intranuclear RNA-binding proteins.



Our findings suggest that the mutant LRSAM1 may aberrantly affect the formation of transcription machinery. Given that a similar mechanism has been reported in motor neuron degeneration of amyotrophic lateral sclerosis, abnormalities of RNA/RNA-binding protein complex may play a role in the neuronal degeneration of CMT2P. Ann Neurol 2016;80:834-845.
Department of Neurology, Center for Human Genetic Research, and Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, TN.
Bo
B
Hu
Department of Neurology, Center for Human Genetic Research, and Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, TN.
Sezgi
S
Arpag
Department of Human Genetics and Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, FL.
Stephan
S
Zuchner
Department of Neurology, Center for Human Genetic Research, and Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, TN.
Jun
J
Li
D000368:Aged; D002460:Cell Line; D002607:Charcot-Marie-Tooth Disease / Q000235:genetics*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D055786:Gene Knockout Techniques; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D008297:Male; D008875:Middle Aged; D020125:Mutation, Missense; D009410:Nerve Degeneration / Q000235:genetics; D009431:Neural Conduction / Q000235:genetics / Q000502:physiology; D009474:Neurons / Q000378:metabolism; D010375:Pedigree; D016601:RNA-Binding Proteins / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics*
D016601:RNA-Binding Proteins; C489657:LRSAM1 protein, human; D044767:Ubiquitin-Protein Ligases