Mitochondrial disease in childhood: mtDNA encoded.

Since the first description of a mitochondrial DNA (mtDNA)-associated disease in the late 1980s, there have been more than 275 mutations within the mtDNA genome described causing human disease. The phenotypic expression of these disorders is vast, as disturbances of the unique physiology of mitochondria can create a wide range of clinical heterogeneity. Features of heteroplasmy, threshold effect, genetic bottleneck, mtDNA depletion, mitotic segregation, and maternal inheritance have been identified and described as a result of novel biochemical and genetic controls of mitochondrial function. We hope that as we unfold this fascinating part of clinical medicine, the reader will see how alterations in the tapestry of mitochondrial biochemistry and genetics can give rise to human illness.