Letter to the Editor: Variable response to Idebenone in LHON is multifactorial.

, We read with interest the article by Mercu ţ et al. about two patients with Leber’s hereditary optic neuropathy (LHON), a 15-year-old male carrying the mitochondrial deoxyribonucleic acid (mtDNA) m.3460G>A variant in MT-ND1 [patient (1)] and an 11-year-old male carrying the m.11778G>A variant in MT-ND4 [patient (2)], in whom the morphological and functional response to Idebenone treatment was monitored in three months intervals over a period of one year [1]. Patient (1) experienced improvement of visual acuity, visual fields defects, and visually evoked potentials (VEPs) but no improvement was found regarding the retinal abnormalities, while patient (2) experienced neither functional nor morphological improvement of his abnormalities [1]. The study is appealing but raises concerns that should be discussed. A limitation of the study is that heteroplasmy rates of the causative mtDNA variants were not provided [1]. Knowing heteroplasmy rates is crucial as they may contribute to the