IARS1 (isoleucyl-tRNA synthetase 1) catalyzes the attachment of isoleucine to its cognate tRNA through a two-step ATP-dependent reaction, enabling accurate protein synthesis 1. The enzyme functions primarily in the cytoplasm and requires t6A modification on tRNAIle for optimal aminoacylation activity 2. IARS1 is essential for embryonic development, as complete knockout causes post-implantation embryonic lethality in mice before organogenesis completion 3. Mutations in IARS1 cause Growth Retardation, Impaired intellectual development, hypotonia, and Hepatopathy (GRIDHH), a rare mitochondrial disease with diverse clinical presentations 4. Key pathological features include intrauterine growth retardation, hepatic dysfunction with fibrosis and steatosis, microcephaly, neurodevelopmental delay, and hypotonia 4. At the molecular level, IARS1 mutations impair mitochondrial function by decreasing mitochondrial membrane potential, increasing reactive oxygen species, and reducing expression of mitochondrial proteins like NME4 5. Clinically, IARS1-deficient individuals present with failure to thrive, feeding difficulties, elevated liver enzymes, cholestasis, and recurrent infections 4. Notably, pulmonary alveolar proteinosis and anemia are associated with poor prognosis 4. Interestingly, under isoleucine deprivation, IARS1 can incorporate valine into proteins at isoleucine codons, a compensatory mechanism absent in IARS1-deficient cells 6.