Abstract - Text

Abstract-Text

Aminoacylation of transfer RNA (tRNA) is a key step in protein biosynthesis, which is carried out by highly specific aminoacyl-tRNA synthetases (ARS). ARS have been implicated in autosomal dominant as well as autosomal recessive human disorders. Autosomal dominant variants in Tryptophanyl-tRNA Synthetase 1 (WARS1) are known to cause a distal hereditary motor neuropathy, but a recessively inherited phenotype is yet to be described. Seryl-tRNA Synthetase 1 (SARS1) has twice been implicated in an autosomal recessive developmental disorder. Here, we report five individuals, from three families, with biallelic missense variants in WARS1 or SARS1, who presented with an overlapping phenotype of microcephaly, developmental delay, intellectual disability, and brain anomalies. Detailed structural mapping showed that the SARS1 variant is located directly within the enzyme"s active site, most likely diminishing its activity, while the WARS1 variant is located in the less well characterized N-terminal domain. We therefore sought to further analyze the mutational effects of the WARS1 variant in patient fibroblasts and in transfected HEK-cells. Preliminary results indicate that mutant WARS1 protein levels might be reduced in comparison to wild-type WARS1 in HEK-cells, hinting at an impact on protein synthesis or degradation. Western-Blot analyses and cycloheximide-chase assays are currently being performed to investigate the abundance and stability of the mutant WARS1 protein. As structural mapping indicated that the variant might affect the structural integrity of WARS1, we are currently using a co-immunoprecipitation assay to test the dimerization capacity of mutant WARS1. Concomitantly, a LC-MS/MS-based enzyme-activity assay is being performed to determine amino acylation efficiency.

In summary, we describe two overlapping autosomal recessive developmental syndromes caused by variants in the tRNA synthetase genes WARS1 and SARS1, present functional insights into the pathogenesis of the novel WARS1-associated syndrome and define an emerging disease spectrum: aminoacyl-tRNA synthetase-associated developmental disorders with or without microcephaly (ARS-DDM).