NDUFA13 and breast cancer: Moreover, knockdown of NDUFB9, NDUFS3, NDUFA13, and NDUFV1 and the consequent reduction of CI activity correlated with increased invasiveness of breast cancer cells [64,65,66], although studies in which these genes are knocked out completely, and CI expression/assembly is abolished are currently lacking, and may be relevant in light of the importance of a functional threshold for a phenotypic effect that this enzyme displays.