Variable genotype of Leber's hereditary optic neuropathy patients

Leber's hereditary optic neuropathy, which often occurs in young adults, causes bilateral loss of central vision. When this neuropathy occurs in families, it can be traced through the mother's line, which suggests that it is caused by mutation of mitochondrial deoxyribonucleic acid (mtDNA). Mitochondria, small structures within the cytoplasm that function in cell metabolism, contain a source of DNA. This mtDNA mutation has been confirmed in Leber's hereditary optic neuropathy, and provides a simple molecular diagnostic test for this disease. A substantial percent of molecules must be mutant for visual loss to occur. A patient demonstrating visual loss will have ancestors with heteroplasmy (both mutant and normal molecules). Since normal molecules reduce the impact of the mutant ones, identification and quantification of heteroplasmy is important. It was found that the proportion of normal and mutant cells varied greatly, not only between generations, but within different tissues from the same person. To determine the mitochondrial genotype (the particular gene configuration on the chromosome) of a patient or family, more than one family member must be tested and more than one type of tissue must be obtained from the individual being tested. (Consumer Summary produced by Reliance Medical Information, Inc.)