Two mtDNA mutations 14487T>C (M63V, ND6) and 12297T>C (tRNA Leu) in a Leigh syndrome family.

Mitochondrial cytopathies are characterized by a large variability of clinical phenotypes and severity. The 14487T>C mutation in mtDNA has been recently described to be associated with Leigh syndrome. The 12297T>C mutation has been described in isolated dilated cardiomyopathy patients. Here, we report a family with multiple members who harbor both mutations, with only a few individuals who are affected with Leigh syndrome. Mitochondrial whole genome sequencing analysis in the proband's muscle specimen detected two nearly homoplasmic mutations: 14487T>C (M63V in ND6) and 12297T>C in the tRNA (Leu) (CUN) gene. These two mutations were also detected in the blood, urine sediments, hair follicles, and buccal swab samples of all matrilineal relatives tested. All individuals tested were nearly homoplasmic for the 12297T>C mutation, but had variable degrees of heteroplasmy for 14487T>C. We also screened for the frequency of these two mutations. Of 268 patients with Leigh or Leigh-like disease, one case was found to harbor the 14487T>C mutation (0.3%), and one had the 12297T>C mutation (0.3%). Neither mutation was detected in the 88 patients meeting MELAS syndrome criteria nor in the 56 patients with respiratory chain complex I or I+III deficiency. In conclusion, the 14487T>C mutation appears as the primary etiology of Leigh syndrome in this family, demonstrating the high level of heteroplasmy needed for a clinically significant phenotype with this mutation. The 12297T>C mutation was not associated with dilated cardiomyopathy for the family members who were clinically evaluated and who were shown by testing to be nearly homoplasmic for that mutation.