RESUMEN
Introduction: Leber hereditary optic neuropathy (LHON) is a mitochondrial disorder that typically presents with painless, central visual loss, hyperaemia of the optic nerve head, and peripapillary telangiectasias. Most LHON cases are due to one of three variants, but several less common variants also exist. We describe a clinical case of LHON associated with the variant m.3866T>C, which is possibly linked to LHON. Case Presentation: A 59-year-old Caucasian woman experienced acute, bilateral, and painless visual loss. She reported cigarette smoking, and elevated phosphatidylethanol suggested harmful alcohol consumption. Her best-corrected visual acuity (BCVA) was 20/100 for the right eye and 20/50 for the left eye. She could only read the Ishihara demonstration plate, and threshold perimetry demonstrated reduced central sensitivity bilaterally. Her optic nerve heads were hyperaemic, with peripapillary telangiectasias. The visual symptoms and clinical findings suggested LHON. Magnetic resonance imaging demonstrated a tuberculum sella meningioma and two cerebral aneurysms, which we regarded as incidental findings. Genetic testing did not identify common LHON variants but a rare homoplasmic variant, m.3866T>C, which studies suggest might cause LHON or act in synergy with other variants to increase the disease penetrance. After initiating test-of-treatment with idebenone 900 mg per day, the patient's BCVA improved to 20/32 for both eyes and then stabilized. Conclusion: This case strengthens the evidence for m.3866T>C as a causative LHON variant. The case also raises the question as to whether this particular variant can respond favourably to treatment with idebenone.