The mitochondrial respiratory chain provides energy to cells via oxidative phosphorylation and consists of four membrane-bound electron-transporting protein complexes (I-IV) and an ATP synthase (complex V) This gene encodes a 51 kDa subunit of the NADH ubiquinone oxidoreductase complex I a large complex with at least 45 nuclear and mitochondrial encoded subunits that liberates electrons from NADH and channels them to ubiquinone This subunit carries the NADH-binding site as well as flavin mononucleotide (FMN)- and Fe-S-biding sites Defects in complex I are a common cause of mitochondrial dysfunction a syndrome that occurs in approximately 1 in 10 000 live births Mitochondrial complex I deficiency is linked to myopathies encephalomyopathies and neurodegenerative disorders such as Parkinson s disease and Leigh syndrome Alternative splicing results in multiple transcript variants encoding distinct isoforms