Abstract

The last decade has been an age of enlightenment as far as mitochondrial pathology is concerned. Well established nuclear genetic diseases, such as Friedreich’s ataxia,^{1 2} Wilson disease,³ and autosomal recessive hereditary spastic paraplegia,⁴ have been shown to have a mitochondrial basis, and we are just starting to unravel the complex nuclear genetic disorders which directly cause mitochondrial dysfunction (table 1). However, in addition to the 3 billion base pair nuclear genome, each human cell typically contains thousands of copies of a small, 16.5 kb circular molecule of double stranded DNA (fig 1). Mitochondrial DNA (mtDNA) accounts for only 1% of the total cellular nucleic acid content. It encodes for 13 polypeptides which are essential for aerobic metabolism and defects of the mitochondrial genome are an important cause of human disease.^{92 93} Since the characterisation of the first pathogenic mtDNA defects in 1988,^{5 13} over 50 point mutations and well over 100 rearrangements of the mitochondrial genome have been associated with human disease^{94 95} (http://www.gen.emory.edu/mitomap.html). These disorders form the focus of this article.