May play some role in mitochondrial processes. Defects in OPA3 are the cause of 3-methylglutaconic aciduria type 3 (MGA3); also known as optic atrophy plus syndrome or Costeff optic atrophy syndrome. MGA3 is an autosomal recessive neuro-ophthalmologic syndrome consisting of early-onset bilateral optic atrophy, spasticity, extrapyramidal dysfunction, and cognitive deficit. Urinary excretion of 3- methylglutaconic acid and 3-methylglutaric acid is increased. MGA3 can be distinguished from MGA1 by the absence of increase of 3- hydroxyisovaleric acid levels. Defects in OPA3 are the cause of optic atrophy type 3 (OPA3); also known as autosomal dominant optic atrophy and cataract (ADOAC) or cataract, optic atrophy and neurologic disorder. Hereditary optic atrophy form a heterogeneous group of disorders. The autosomal dominant forms are characterized by an insidious onset of visual impairment in early childhood with moderate to severe loss of visual acuity, temporal optic disk pallor, color vision deficits and centrocecal scotoma of variable density. Belongs to the OPA3 family. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.