Purpose: To investigate the prevalence and spectrum of mitochondrial ND4 mutations in subjects with Leber's hereditary optic neuropathy (LHON).

Methods: A cohort of 1281 Chinese Han probands and 478 control subjects underwent clinical and genetic evaluation, and sequence analysis of mitochondrial (mt) DNA, as well as enzymatic assay of NADH: ubiquinone oxidoreductase.

Results: In this cohort, 503 probands had a family history of optic neuropathy and 778 subjects were sporadic cases. Mutational analysis of ND4 gene identified 149 (102 known and 47 novel) variants. The prevalence of known m. 11778G> A mutation was 35.36%. Furthermore, we identified the known m. 11696G> A and m. 11253T> C mutations and five novel putative LHON-associated mutations. These mutations accounted for 2.74% of cases of LHON subjects. By enzymatic assay, we showed a mild decrease in the activity of NADH: ubiquinone oxidoreductase in mutant cell lines carrying only one putative mtDNA mutation. The low penetrance of optic neuropathy and mild biochemical defects in these pedigrees carrying only m. 11696G> A mutation and one putative LHON-associated mutation suggested that the mutation (s) is (are) necessary but is (are) itself (themselves) insufficient to produce a visual failure. Moreover, mtDNAs in 169 probands carrying the LHON-associated mutation (s) were widely dispersed among 13 Eastern Asian haplogroups. In particular, the frequencies of haplogroups D, M8, M10, M11, and H in probands carrying the LHON-associated mtDNA mutation (s) were higher than those in Chinese controls.

Conclusions: These results suggested that the ND4 gene is the hot spot for mutations associated with LHON. Thus, these findings may provide valuable information for the further understanding of pathogenic mechanism of LHON.