Multiple mitochondrial dysfunctions syndrome is a rare condition; its prevalence is unknown. It is one of several conditions classified as mitochondrial disorders, which affect an estimated 1 in 5,000 people worldwide.

Multiple mitochondrial dysfunctions syndrome can be caused by mutations in the NFU1 or BOLA3 gene. The proteins produced from each of these genes appear to be involved in the formation of molecules called iron-sulfur (Fe-S) clusters or in the attachment of these clusters to other proteins. Certain proteins require attachment of Fe-S clusters to function properly.

The NFU-1 and BOLA3 proteins play an important role in mitochondria. In these structures, several proteins carry out a series of chemical steps to convert the energy in food into a form that cells can use. Many of the proteins involved in these steps require Fe-S clusters to function, including protein complexes called complex I, complex II, and complex III.

Fe-S clusters are also required for another mitochondrial protein to function; this protein is involved in the modification of additional proteins that aid in energy production in mitochondria, including the pyruvate dehydrogenase complex and the alpha-ketoglutarate dehydrogenase complex (also known as the oxoglutarate dehydrogenase complex). This modification is also critical to the function of the glycine cleavage system, a set of proteins that breaks down a protein building block (amino acid) called glycine when levels become too high.

Mutations in the NFU1 or BOLA3 gene reduce or eliminate production of the respective protein, which impairs Fe-S cluster formation. Consequently, proteins affected by the presence of Fe-S clusters, including those involved in energy production and glycine breakdown, cannot function normally. Reduced activity of complex I, II, or III, pyruvate dehydrogenase, or alpha-ketoglutarate dehydrogenase leads to potentially fatal lactic acidosis, encephalopathy, and other signs and symptoms of multiple mitochondrial dysfunctions syndrome. In some affected individuals, impairment of the glycine cleavage system leads to a buildup of glycine.