Leber’s Hereditary Optic Neuropathy

Four new missense mutations have been identified through restriction analysis and sequencing of the mitochondrial DNAs (mtDNA) from Leber’s hereditary optic neuropathy (LHON) patients who lacked the previously identified 1 1778 mutation. Each altered a conserved amino acid and correiated with the LHON phenotype in population and phylogenetic analyses. The nucleotide pair (np) 13708 mutation (G to A, ND5 gene) changed an alanine to a threonine and was found in 6/25 (24%) of non1 1778 LHON pedigrees and in 5.0% of controls, the np 15257 mutation (G to A, cytochrome b gene) changed an aspartate to an asparagine and was found in 4 of the 13708-positive pedigrees and 0.3% of controls, the np 15812 mutation (G to A, cytochrome b gene) changed a valine to a methionine and was detected in two of the 15257-positive pedigrees and 0.1% of controls and the np 5244 mutation (G to A, ND2 gene) changed a glycine to a serine and was found in one of the 15812positive patients and none of 2103 controls. The 15257 mutation altered a highly conserved amino acid in an extramembrane domain of cytochrome b that is associated with the ligation of the low potential bscici heme and the 5244 mutation altered a strongly evolutionarily conserved region of the ND2 polypeptide. The 13708 and 15812 mutations changed moderately conserved amino acids. Haplotype and phylogenetic analysis of the four np 15257 mtDNAs revealed that all harbored the same rare Caucasian haplotype and that the np 13708, np 15257, np 15812 and np 5244 mutations were added sequentially along this mtDNA lineage. Since the percentage of sighted controls decreases as these mutations accumulate, it appears that they interact synergistically, each increasing the probability of blindness. The involvement of both mitochondrial complex I (np 5244, 1 1778, 13708) and complex 111 (np 15257, 15812) mutations in LHON indicates that the clinical manifestations of this disease are the product of an overall decrease in mitochondrial energy production rather than a defect in a specific mitochondrial enzyme. L EBER’S hereditary optic neuropathy (LHON) is a maternally inherited disease of young adults which results in rapid bilateral loss of central vision due to optic nerve death (NEWMAN and WALLACE 1990). Penetrance is variable along homoplasmic maternal lineages and the disease exhibits a male bias with an overall ratio of greater than 2 affected males to 1 affected female (NEWMAN and WALLACE 1990). The maternal transmission of LHON suggested that this disease might be due to a mitochondrial DNA (mtDNA) mutation (GILES et al. 1980). Th’ 1s was confirmed by the discovery of a G to A transition mutation at nucleotide pair (np) 11778 in the mtDNAs of 9 of 1 1 LHON pedigrees (WALLACE et al. 1988). This mutation replaces an arginine with a histidine at position 340 in the ND4 gene of the mitochondrial NADHxbiquinone oxidoreductase (respiratory complex I) and eliminates a SfaNI restriction enzyme recognition site. Several lines of evidence indicate that the 1 1778 mutation is the cause of most LHON cases. The mutation alters an evolutionary conserved amino Genetics 130: 163-173 (January, 1992) acid, is found in 50% to 80% of LHON patients but not controls, correlates with the symptoms regardless of mtDNA haplotype, and can be heteroplasmic (WALLACE et al. 1988; SINGH, LOTT and WALLACE 1989; LOTT, VOLJAVEC and WALLACE 1990; HOLT, MILLER and HARDINC 1989). While the majority of LHON cases can be attributed to the 11778 mutation, other LHON patients do not have this mutation. We now describe the mtDNA sequence of a nom11778 patient and provide evidence that the primary cause of the disease in this patient and three others is a mutation in a highly conserved amino acid of the mtDNA cytochrome b gene of respiratory complex 111. Three additional mutations, in the ND2, ND5 and cytochrome b genes, were also found which appear to augment the deleterious effects of this mutation. MATERIALS AND METHODS LHON patients and controls: Twenty-five non-11778 LHON families, 24 11 778 LHON families and 292 controls 164 M. D. Brown et al.