A mitochondrial disorder with ptosis and exercise intolerance without ophthalmoparesis secondary to m.5865 T > C variant

We describe a novel mitochondrial variant (m.5865 T > C) in a patient with decreased exercise endurance and juvenile onset slowly progressive bilateral ptosis without ophthamloparesis. The m.5865 T > C variant was seen in 82.9% of mtDNA molecules in skeletal muscle tissue and ~8% of mtDNA molecules in urine epithelium, but was not detected in blood leukocytes. The proband does not demonstrate any additional features often seen in individuals with a mitochondrial disorder (i.e., sensorineural hearing loss, type 2 diabetes, stroke-like episodes, muscle weakness, ophthalmoparesis, cardiomyopathy or cardiac arrhythmias). This case suggests that ptosis and exercise intolerance, without ophthalmoparesis, are the primary clinical features of the m.5865 T > C mtDNA variant.