A systematic analysis of mitochondrial aminoacyl tRNA synthetase variants in a rare disease cohort

Mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs) are a group of proteins encoded by nuclear DNA that play a crucial role in mitochondrial protein synthesis. Mitochondrial diseases caused by mt-aaRS variants are phenotypically heterogenous but often present with significant neurological features such as childhood-onset encephalopathy and seizures. As such, these conditions are a diagnostic challenge. We present an approach that systematically quantifies phenotypic similarity of individuals with an mt-aaRS variant to published cases, to aid variant interpretation, in RD-Connect-a large Europe-wide rare disease cohort. Across 98 individuals with a mt-aaRS gene of interest, we prioritised 38 individuals with 63 variants following bioinformatic and manual analyses. We additionally reviewed Exomiser prioritisation using a pre-defined gene list for neurological disorders within the RD-Connect Genome-Phenome Analysis Platform (GPAP). We were able to generate likely diagnoses in 11 individuals and VUS findings in 13 individuals, following careful phenotype similarity analysis using a phenotype-genotype dataset generated from 234 published individuals. Four of these 24 individuals did not have an Exomiser-ranked gene variant in the GPAP. Therefore, this approach, using individual-level curated phenotype-genotype data to support variant interpretation, can highlight potentially significant variants that may not be captured by current pipelines. This workflow can be replicated in other heterogeneous rare diseases to support clinical practice.