Mitochondrial haplogroup D4j specific variant m.11696G>a(MT-ND4) may increase the penetrance and expressivity of the LHON-associated m.11778G>a mutation in Chinese pedigrees

Leber's hereditary optic neuropathy (LHON) is one of the most common mitochondrial disorders. We report here the clinical, genetic and molecular analysis of mitochondrial DNA (mtDNA) in eight Han Chinese families carrying the known mitochondrial 11778G>A(MT-ND4) mutation. Thirty-seven (26 males/11 females) of 77 matrilineal relatives in these families exhibited the variable severity and age-at-onset of optic neuropathy. The penetrances were from 25% to 75%, with the average of 42%, and the age-at-onset for visual impairment varied from 10 to 25 years, with the average of 17 in these Chinese pedigrees. Molecular analysis of their mtDNA identified distinct sets of variants belonging to the Eastern Asian haplogroupD4j. Except the known m.11778G>A mutation, the m. 11696G>A(MT-ND4) mutation caused the substitution of an isoleucine for valineat amino acid position 313, located in a predicted transmembrane region of ND4. And, it is reported that the m. 11696G>A mutation was associated with LHON, and appeared to contribute to higher penetrance in these nine Chinese families than other Chinese families carrying only the m. 11778G>A mutation. Therefore, the mitochondrial haplogroup D4j specific m. 11696G>A mutation may act in synergy with the primary LHON-associated m.11778G>A mutation, thereby increasing the penetrance and expressivity of visual loss in these Chinese families.