For example, a cardiac-specific KO (cKO) of PGC-1α/β in postnatal mice caused mitochondrial fragmentation and altered expression of mitochondrial fusion (MFN1, OPA1) and fission (DRP1, FIS1) genes, and a decrease in mitochondrial respiration, finally culminating in lethality due to cardiomyopathy (Martin et al., 2014). The gene discussed is MFN1; the disease is cardiomyopathy.