A novel missense mutation of CMT2P alters transcription machinery

Abstract

Objective Charcot-Marie-Tooth type 2P (CMT2P) has been associated with frame-shift 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. Methods 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. Results 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 co-segregated 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. Interpretation Our findings suggest that the mutant LRSAM1 may aberrantly affect the formation of transcription machinery. Given 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.

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“…provided by Medical Neurogenetics (Atlanta, GA, USA). The test sequenced 42 CMT-related genes and mitochondrial DNA as described previously [6].…”