MT-ATP6 and Down syndrome: Based on the previously described clinical syndromes associated with MT-ATP6/8 defects, 3 patients (3%) met the criteria for CPEO + syndrome (chronic progressive external ophthalmoplegia with multisystemic features), 10 patients (9.0%) for NARP syndrome (NARP), 9 patients (8%) for classic Leigh syndrome (LS) with exclusively neurologic signs/symptoms, and 45 patients (41%) for Leigh-like syndrome with multisystemic involvement (LS+) while 44 patients (40%) presented with miscellaneous other phenotypes.