A novel mtDNA C11777A mutation in Leigh syndrome.

A novel mitochondrial DNA point mutation, a C-to-A mutation at nucleotide position (np) 11,777, was identified in two unrelated patients out of 100 with Leigh syndrome. This mutation converted a highly evolutionary conserved arginine to a serine at codon 340 in ND4 gene. This codon was also converted by a G-to-A mutation at np 11,778, the most common mutation associated with Leber's hereditary optic neuropathy (LHON), but the amino acid replacement was different (R340S vs. R340H). Cybrid study revealed that the percentage of heteroplasmy was correlated with complex I function and that the novel mutation caused a much more deleterious effect than the np 11,778 LHON mutation in complex I activity.