MCAT and External ophthalmoplegia: We also counted the number of deletions in the cytochrome c oxidase genes (MT‐CO, including MT‐CO1, MT‐CO2, and MT‐CO3) and mitochondrial cytochrome b genes (MT‐CYB), and calculated that patients with KSS had more deletions in both MT‐CO and MT‐CYB genes than patients with CPEO [median (IQR): 1.50 (1) vs. 1 (0) for MT‐CO, p < 0.001; 0 (1) vs. 0 (0) for MT‐CYB, p = 0.006].