Comparison of mtDNA copy number between the MDD group and the HC group, and comparison of mtDMA copy number within the MDD group.

MDD: major depressive disorder; HC: healthy controls; HDRS: Hamilton Depression Rating Scale. p calculated by the t-test. * Patients are considered to be currently suffered from depression with a score of ≥18 on the HDRS, while are defined as being in remission if they had an HDRS score less than 18.