Lactic acidemia and mitochondrial disease.

Lactic acidemia is present in the majority of patients with mitochondrial oxidative defects as well as in disorders of gluconeogenesis. An understanding of the dynamics of lactic acid metabolism in the human body and the influences on lactate/pyruvate ratios exerted by changes in cellular redox state allows for the development of diagnostic algorithms based on clinical and biochemical phenotypes. Mitochondrial disorders can be due to defects in nuclear genes directly affecting the respiratory chain assembly or function, mtDNA genes affecting the respiratory chain or nuclear genes influencing mtDNA structure and viability. In this review, we look at the classification of mitochondrial disease from the perspective of not just the genetic and biochemical etiology but also from the perspective of the clinical phenotypic expression.