New understanding and treatment of adult mitochondrial dysfunction: an example of personalized precision medicine.

The principal cellular energy-generating pathways of mitochondria used to produce adenosine triphosphate (ATP) are oxidative phosphorylation and β-oxidation of fatty acids. Under anaerobic conditions, glycolysis in the cytoplasm is an alternative mechanism for production of ATP. Mitochondrial diseases result from one or more of the over 350 mutations in mitochondrial DNA (10%) or nuclear DNA (90%) that cause defective mitochondrial ATP production. The most common manifestations in adults with mitochondrial DNA mutations are diminished vision, myopathy, cardiomyopathy, neuropathy, encephalopathy and diabetes. Uncommonly there are stroke-like syndromes. The most common manifestations in adults with nuclear DNA mutations are neuropathy with prominent ataxia, ophthalmoplegia, dysarthria, myopathy, cardiomyopathy, liver disease, neuroendocrine and renal cell tumors, and hypoglycemia. Adults, especially the elderly, may only develop manifestations in the course of stressful illnesses that unmask these mutations. Children may require mitochondrial transfer or gene editing therapy. These mutations should be sought in leukocytes or muscle tissue in adults who do not respond to usual treatment for severe stressful illnesses as they may benefit from newly-approved medications.