OPA1 and progressive external ophthalmoplegia: Recently, mutations in OPA1 and MFN2 have been described in patients with autosomal dominant optic atrophy (ADOA) and multisystem clinical involvement (including progressive external ophthalmoplegia (PEO)) who harbored mitochondrial DNA (mtDNA) deletions in skeletal muscle [16–18] (Table 1, Figure 1(a)).