부산대학교 도서관

Unlike most other structures within cells, the mitochondrion carries its own DNA. The majority of proteins in a mitochondrion are specified by DNA carried on the chromosomes in the nucleus of the cell, as are the other cellular proteins, but a small fraction of mitochondrial proteins is specified by the mitochondrial DNA (mtDNA) itself. In recent years, it has become clear that some unusual syndromes are the result of mutations in the mtDNA. Since the mitochondria of a person derive exclusively from the mitochondria present in the egg before fertilization, the inheritance of mitochondrial DNA defects is entirely maternal. The authors describe the results of analysis of mitochondrial DNA in 56 patients with features suggestive of mitochondrial abnormalities. One of the key diagnostic features of a mitochondrial abnormality is the appearance of the so-called 'ragged-red muscle' fibers under the microscope. A particularly specific symptom of mitochondrial abnormality is progressive external ophthalmoplegia, in which the muscles for eye movement slowly fail; patients are also likely to be weak and to have heart contraction problems. Kearns-Sayre syndrome is a condition that has been well-established to be a result of abnormalities in mtDNA. In the present series of patients, genetic analysis revealed deletions of mtDNA in 19 cases. In a deletion mutation, an entire stretch of DNA is missing, rather than merely altered as in some other types of mutation. Deletion mutations are usually the most severe. In the 19 cases described here, the size of the deletion appeared to correlate inversely with the age of the patient at the onset of disease symptoms; the more DNA that was missing, the younger the patient was likely to be at the disease onset. In one of two patients for whom a more precise analysis of mtDNA was carried out, it was found that there were several different deletions present in the purified mitochondrial DNA. The authors suggest that this unusual finding may be obscured when the DNA from the entire muscle is analyzed, rather than the DNA from purified mitochondria. Such multiple abnormalities may therefore be more common than suspected. (Consumer Summary produced by Reliance Medical Information, Inc.)