MT-ND4 and nervous system disorder: The network was built around hub genes involved in the mitochondrial respiratory chain, including a number of the NADH hydrogenase subunits, such as ND1, ND2, ND4, ND5 and ND6, as well as, COX1, Atp5j2, and CYTB. Mitochondrial dysfunction and dysfunctional energy metabolism are early pathological features of multiple neurological diseases, including Alzheimer’s disease, Parkinson’s disease and Huntington’s disease [34, 46].