MT-CO1 and hydrops fetalis: Finally, transcripts for three key enzymes in the electron transport chain were significantly upregulated in HF (Figure 4E) and are highlighted red in the metabolic pathway (Figure 4A); mt-Nd5 is responsible for NADH dehydrogenase 5, part of complex I, and mt-Co1 and Cox5a are responsible for cytochrome c oxidase subunits I and 5a of complex IV.