Is a novel I214M substitution in the NEFL gene a cause of Charcot-Marie-Tooth disease? Functional analysis using cell culture models

Recent studies have shown that mutations in neurofilament light subunit gene (NEFL) cause Charcot-Marie-Tooth (CMT) disease. Since the first description of the Gln333Pro mutation in the NEFL gene, 10 pathogenic mutations in the NEFL gene have been reported in patients affected with CMT disease. We report a novel I214M amino acid substitution in the NEFL gene in two unrelated patients affected with CMT. Because the I214M amino acid substitution in the NEFL protein was not detected in a CMT af- fected brother of the proband, its pathogenic effect became unclear. In order to deter- mine whether this amino acid substitution is a benign polymorphism or causative of the disease, we performed a functional analysis of the mutant I214M neurofilament protein (NFL). Transfections of the mutant protein in cultured cells revealed an increased ten- dency to form highly compacted filamentous structures but no other alterations of neuro- filament assembly or transport were observed. Furthermore, the sibling of one of the patients was also affected with CMT but did not have the I214M substitution. These data suggest that this I214M substitution in the NEFL gene was not a direct cause of the dis- ease but could be a polymorphism or possibly a modifier of the CMT phenotype.