Furthermore, another recessive form of isolated or syndromic optic neuropathy associated with mutations in the Reticulon 4 Interacting Protein 1 (RTN4IP1) gene (OPA10) has been reported to present with a combined defect of complex I and IV [57], but also with a profound complex I defect when associated with the severe phenotype [58]. Here, RTN4IP1 is linked to optic nerve disorder.