A patient presenting with encephalo-cardiomyopathy in the neonatal period was reported to be homozygous for a COX18 mutation that results in an D223H substitution, at a residue that is highly conserved, even in the distantly related OXA1L [140]; thus far, this is the only reported case of mutations in COX18 underlying a mitochondrial disease phenotype. Here, OXA1L is linked to mitochondrial disease.