TRMU and Decreased liver function: However, reversible infantile respiratory chain deficiency (RIRCD), due to a homoplasmic mt-tRNAGlu mutation, and reversible infantile hepatopathy, due to tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase (TRMU) deficiency, stand out by showing spontaneous recovery, and provide the key to treatments of potential broader relevance.