Recessive, pathogenic AARS1 variants display variable loss-of-function and dominant-negative effects.

Alanyl-tRNA synthetase 1 (AARS1) has been implicated in multi-system recessive phenotypes and in later-onset dominant neuropathy; to date, no single variant has been associated with both dominant and recessive diseases, raising questions about shared mechanisms between the two inheritance patterns. AARS1 variants associated with recessive disease result in loss-of-function or hypomorphic alleles, and this has been demonstrated, in part, via yeast complementation assays. However, pathogenic alleles have not been assessed in a side-by-side study. Here, we employed a humanized yeast model to evaluate the functional consequences of all AARS1 missense variants reported in recessive disease. The majority of variants showed variable loss-of-function effects, ranging from no growth to significantly reduced growth. These data deem yeast a reliable model to test the effects of AARS1 variants; however, our data also indicate that this model is prone to false-negative results and is not informative for genotype-phenotype studies. We next tested missense variants associated with no growth for dominant-negative effects. Interestingly, K81T and E99G AARS1 demonstrated both loss-of-function and dominant-negative effects, indicating that certain AARS1 variants can cause both dominant and recessive disease phenotypes.