Gastrointestinal and hepatic manifestations of mitochondrial disorders

Inherited defects of oxidative phosphorylation lead to heterogeneous, often multisystem, mitochondrial diseases. This review highlights those mitochondrial syndromes with prominent gastrointestinal and hepatic symptoms, categorised according to underlying disease mechanism. Mitochondrial encephalopathies with major gastrointestinal involvement include mitochondrial neurogastrointestinal encephalopathy and ethylmalonic encephalopathy, which are each associated with highly specific clinical and metabolic profiles. Mitochondrial hepatopathies are most frequently caused by defects of mitochondrial DNA maintenance and expression. Although mitochondrial disorders are notorious for extreme clinical, biochemical and genetic heterogeneity, there are some pathognomonic clinical and metabolic clues that suggest a specific diagnosis, and these are highlighted. An approach to diagnosis of these complex disorders is presented, together with a genetic classification, including mitochondrial DNA disorders and nuclear-encoded defects of mitochondrial DNA maintenance and translation, OXPHOS complex assembly and mitochondrial membrane lipids. Finally, supportive and experimental therapeutic options for these currently incurable diseases are reviewed, including liver transplantation, allogeneic haematopoietic stem cell transplantation and gene therapy.