MT-ATP8 variants or variants in the overlapping regions between MT-ATP6 and MT-ATP8 are instead more recent discoveries with a few reported patients in literature with a phenotype including cardiomyopathy, diabetes, encephalopathy, peripheral neuropathy, and progressive external ophthalmoplegia.18, -, 21 The overall clinical variability of MT-ATP6/8 deficiency challenges the design of clinical trials and the development of novel experimental therapy. Here, MT-ATP6 is linked to progressive external ophthalmoplegia.