MFN2 and optic atrophy: For the selection of putative disease-causing genes, we considered a sub panel of genes associated with optic atrophy, including OPA1, OPA3, TMEM126A, WFS1, MFN2, SPG7, ACO2, RTN4IP1 and AFG3L2, and identified one male individual with the heterozygous deletion c.1699_1749del51 in the ACO2 gene (NCBI reference NM_001098.3; hereafter referred to as ACO2-mutant or ACO2.mut) (Fig. 1a; individual III.4).