Further, we show that compound-dependent activation of the ISR reduces the population of fragmented mitochondria and rescues basal mitochondrial network morphology in patient fibroblasts expressing the D414V variant of the pro-fusion GTPase MFN2 associated with a complex clinical phenotype including ataxia, optic atrophy, and sensorineural hearing loss (Sharma et al., 2021b). This evidence concerns the gene MFN2 and hereditary optic atrophy.