Mitochondrial methionyl-tRNA-formyltransferase (MTFMT) is essential for mitochondrial protein translation. The MTFMT gene encodes for an enzyme of the same name, which acts to formylate the methionine of mitochondrial Met-tRNA(Met). In Homo sapiens, MTFMT-formylated-tRNA is an initiator and elongator for the synthesis of 13 mitochondrially-encoded proteins in complexes I, III and IV of the ETC. To understand this mechanism, it is necessary to perform a comprehensive analysis of energy metabolism and oxidative phosphorylation (OXPHOS) among impacted patients. Alterations to this gene vary, with the most documented as a single-splice-site mutation (c.626C>T). Here, we discuss MTFMT involvement in mitochondrial protein translation and neurodegenerative disorders, such as Leigh Syndrome and combined OXPHOS deficiency, in two families. We aim to delineate the impact of OXPHOS dysfunction in patients presenting with MTFMT mutation.