Abstract for presentation at 11th International Congress of Human Genetics

Charcot-Marie-Tooth (CMT) disease and distal spinal muscular atrophy (dSMA) are peripheral nerve disorders characterized by distal muscle weakness and wasting. CMT2D and dSMA-V are subtypes that show an autosomal dominant mode of inheritance and a more severe phenotype in the upper extremities. We previously identified multiple disease-causing mutations in the glycyl-tRNA synthetase (GARS) gene in patients with CMT2D or dSMA-V. GARS is a member of the family of aminoacyl-tRNA synthetases responsible for charging tRNA with cognate amino acids; GARS ligates glycine to tRNAGLY. We have pursued four lines of study to investigate the mechanism(s) by which GARS mutations cause peripheral neuropathy. First, northern and western blot analyses indicated the absence of mutation-associated changes in GARS expression levels. Second, in vivo yeast complementation assays revealed that the majority of mutations modeled in the yeast ortholog (GRS1) severely impair viability. Third, the majority of EGFP-tagged GARS variants containing disease-associated mutations mislocalize when expressed in neuronal cells. Indeed, 4 of the 5 mutations studied were found to show loss-of-function features in at least one assay, suggesting that tRNA-charging deficits may be involved in disease pathogenesis. Finally, and in support of this notion, we found endogenous GARS-associated granules present in the neurite projections of normal cultured neurons and in peripheral nerve axons in normal human tissue sections. Importantly, our studies are consistent with the recent identification and characterization of CMT-associated mutations in another tRNA synthetase gene (YARS). These data suggest that tRNA-charging enzymes play a role in maintaining neuronal health and that all genes in this family should be studied for their possible role in inherited neuropathies.