Novel NARS2 variant causing leigh syndrome with normal lactate levels.

Leigh syndrome is the most genetically heterogenous phenotype of mitochondrial disease. We describe a patient with Leigh syndrome whose diagnosis had not been confirmed because of normal metabolic screening results at the initial presentation. Whole-exome sequencing identified pathogenic variants in NARS2, the gene encoding a mitochondrial asparaginyl-tRNA synthetase. One of the biallelic variants was novel. This highlights the essential role of genetic testing for a definite diagnosis of Leigh syndrome.