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The rare autosomal dominant Charcot-Marie-Tooth type 2B (CMT2B) is associated with mutations in the RAB7A gene, involved in the late endocytic pathway. CMT2B is characterized by predominant sensory loss, ulceromutilating features, with lesser-to-absent motor deficits. We characterized clinically and genetically a family harboring a novel pathogenic RAB7A variant and performed structural and functional analysis of the mutant protein. A 39-year-old woman presented with early-onset walking difficulties, progressive distal muscle wasting and weakness in lower limbs and only mild sensory signs. Electrophysiology demonstrated an axonal sensorimotor neuropathy. Nerve biopsy showed a chronic axonal neuropathy with moderate loss of all caliber myelinated fibers. Next-generation sequencing (NGS) technology revealed in the proband and in her similarly affected father the novel c.377A>G (p.K126R) heterozygous variant predicted to be deleterious. The mutation affects the biochemical properties of RAB7 GTPase, causes altered interaction with peripherin, and inhibition of neurite outgrowth, as for previously reported CMT2B mutants. However, it also shows differences, particularly in the epidermal growth factor receptor degradation process. Altogether, our findings indicate that this RAB7A variant is pathogenic and widens the phenotypic spectrum of CMT2B to include predominantly motor CMT2. Alteration of the receptor degradation process might explain the different clinical presentations in this family.

Charcot-Marie-Tooth disease type 2 (CMT2) is an autosomal dominant axonal neuropathy caused by mutations in various genes. The subtype CMT2B results from missense mutations in RAB7A, member RAS oncogene family gene, whereas missense mutations in the Leucinerich repeat and sterile alpha motif-containing protein 1 (LRSAM1) gene cause CMT2P. We describe the genotype/phenotype analysis of a family in which a previously described mutation in the RAB7A gene and a novel mutation in the LRSAM1 gene were identified. In this family, none of the individuals had ulceromutilating features, and there was a marked variability in the age of onset. We discuss the possible etiology of the observed phenotypic variability including the role of gender and possible RAB7A/LRSAM1 gene interactions. [ABSTRACT FROM AUTHOR]

Sensory loss and ulcero-mutilating features have been observed in hereditary sensory neuropathy type I and in hereditary motor and sensory neuropathy type IIB, also referred as Charcot–Marie–Tooth disease type 2B. To date two loci associated with ulcero-mutilating neuropathy have been described: CMT2B at 3q13–q22 and HSN I at 9q22.1–q22.3. We performed linkage analysis with chromosomal markers representing the hereditary sensory neuropathy type I and Charcot–Marie–Tooth disease type 2B loci on an Italian family with a severe distal sensory loss leading to an ulcero-mutilating peripheral neuropathy. Negative likelihood-of-odds scores excluded any evidence of linkage to both chromosome 3q13 and chromosome 9q22 markers, confirming the genetic heterogeneity of this clinical entity and the presence of a third locus responsible for ulcero-mutilating neuropathies. [Copyright &y& Elsevier]

The rare autosomal dominant Charcot-Marie-Tooth type 2B (CMT2B) is associated with mutations in the RAB7A gene, involved in the late endocytic pathway. CMT2B is characterized by predominant sensory loss, ulceromutilating features, with lesser-to-absent motor deficits. We characterized clinically and genetically a family harboring a novel pathogenic RAB7A variant and performed structural and functional analysis of the mutant protein. A 39-year-old woman presented with early-onset walking difficulties, progressive distal muscle wasting and weakness in lower limbs and only mild sensory signs. Electrophysiology demonstrated an axonal sensorimotor neuropathy. Nerve biopsy showed a chronic axonal neuropathy with moderate loss of all caliber myelinated fibers. Next-generation sequencing (NGS) technology revealed in the proband and in her similarly affected father the novel c.377A>G (p.K126R) heterozygous variant predicted to be deleterious. The mutation affects the biochemical properties of RAB7 GTPase, causes altered interaction with peripherin, and inhibition of neurite outgrowth, as for previously reported CMT2B mutants. However, it also shows differences, particularly in the epidermal growth factor receptor degradation process. Altogether, our findings indicate that this RAB7A variant is pathogenic and widens the phenotypic spectrum of CMT2B to include predominantly motor CMT2. Alteration of the receptor degradation process might explain the different clinical presentations in this family. [ABSTRACT FROM AUTHOR]