A case of late‐onset Leber's hereditary optic neuropathy with elevated serum lactic acid and pyruvic acid levels by cycle ergometer exercise

Leber's hereditary optic neuropathy ( LHON ) is a mitochondrial disorder characterized by acute or subacute bilateral vision loss. We describe a female who experienced visual impairment at the age of 75 years. Genetic analysis of peripheral blood leukocytes revealed a point mutation (11778G>A) in MTND 4 encoded by mitochondrial DNA . The most distinctive feature of our patient was the elevation of serum LA and PA levels and the LA / PA ratio by cycle ergometer exercise without clinical or pathological skeletal muscle involvement. Also, droplet digital PCR (dd PCR ) showed that mutation fractions of m.11778G>A in peripheral blood and muscle sample were higher than 99.9%, indicating “homoplasmy”. Although no cases of LHON with clinical impairment of skeletal muscle have been reported, subclinical mitochondrial dysfunction has been reported. We concluded that the ergometer test sensitively detected a subclinical change caused by mitochondrial respiratory chain dysfunction, showing the diversity of genotype and phenotype relationship in LHON .