A heteroplasmic mutation in the NADH dehydrogenase subunit 5 gene (ND5), identified in colorectal tumors [47], disrupts the synthesis of the ND5 subunit of Complex I and subsequently hinders the proper assembly of Complex I. This causes an increase in mtROS levels and enhanced tumorigenicity [48]. The gene discussed is MT-ND5; the disease is colorectal neoplasm.