Revisiting the issue of mitochondrial DNA content in optic mitochondriopathies.

Involvement of the visual system in mitochondrial diseases, in particular of retinal ganglion cells (RGCs) and the optic nerve, is very common and has been defined "optic mitochondriopathies."(1) The prototype is Leber hereditary optic neuropathy (LHON, OMIM 535000), the first disease to be associated with a mitochondrial DNA (mtDNA) point mutation and now considered the most frequent mitochondrial disease.(2) LHON has been joined by dominant optic atrophy (DOA, OMIM 165500) Kjer type, which in a large set of cases is associated with heterozygous mutations in the nuclear gene OPA1 encoding for a mitochondrial fusion protein.(2) Both disorders have features in common: clinically the preferential involvement of the papillomacular bundle and central vision, biochemically a defective respiratory chain and an increased propensity toward apoptosis.(2).