During normal erythropoiesis, the conversion of uridine to pseudouridine in transfer RNAs (tRNAs) by PUS1 promotes mitochondrial tRNA stability and regulates protein synthesis rates and mitochondrial function. In MLASA, mutations in PUS1 lead to loss of mitochondrial tRNA pseudouridylation and a subsequent decrease in mitochondrial tRNA abundance, which impairs erythropoiesis through dysregulated protein synthesis, disruption of oxidative phosphorylation, and activation of the mammalian target-of-rapamycin pathway.