Indeed, high abundances of deletions involving ND2 and ND4, two mtDNA genes that code for NADH-ubiquinone oxidoreductase, an essential respiratory protein complex, were found in the spinal cord of ALS patients, supporting the concept that some motor neurons in ALS may die because of a deficit in the mitochondrial ATP production and cellular energy metabolism (Fig. 4) [102]. Here, MT-ND4 is linked to amyotrophic lateral sclerosis.