Background: Leber's hereditary optic neuropathy is associated with four known pathogenetic mutations of mitochondrial DNA (mtDNA) at nucleotide positions (np) 11778, 3460, 15257, and 14484. Methods: The authors collected clinical data from 12 visually symptomatic patients from seven different pedigrees with the 15257 mutation and compared these data with previously published clinical features of the 11778 and 3460 mutations. Results: The authors' results indicate that these three groups of patients are similar in most clinical characteristics evaluated. However, patients with the 15257 mutation are more likely to experience significant recovery of visual acuity than patients with the 11778 mutation (25% versus 4% of eyes; P < 0.001). Patients with the 15257 mutation who also have an associated mutation at np 15812 are less likely to recover vision than those without this association (P = 0.001). Patients with the 15257 mutation also have a higher incidence of spinal cord and peripheral neurologic symptoms (42%) than patients with the other pathogenetic mutations. Conclusions: The phenotypic expression of the 15257 mutation differs from the 11778 and 3460 mutations and is affected by the presence of an associated mutation at np 15812. This is the first clinical evidence to support the concept of multiple simultaneous mtDNA mutations producing additive deleterious effects in patients with Leber's hereditary optic neuropathy. The clinical differences between the various genotypes associated with Leber's hereditary optic neuropathy have implications for risk factor management and visual prognosis and, thus, underscore the importance of molecular genetic testing in patients with suspected Leber's hereditary optic neuropathy.
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