Accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), that is believed not to be involved in catalysis. Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone. Mammalian complex I is composed of 45 different subunits (PubMed:12611891, PubMed:27626371). This is a component of the iron-sulfur (IP) fragment of the enzyme (PubMed:12611891). The disease is caused by variants affecting the gene represented in this entry. Belongs to the complex I NDUFS6 subunit family.