First identified in 2011, deleterious variants in the genes encoding for five of these proteins, NFU1, BOLA3, IBA57, ISCA2, and ISCA1, lead to a disease named multiple mitochondrial dysfunction syndrome (MMDS) types 1 to 5, respectively, with symptoms indicative of a general decreased energy metabolism and mitochondrial respiration failure. This evidence concerns the gene NFU1 and Fatal multiple mitochondrial dysfunction syndrome type 2.