title: Leukocyte mitochondrial DNA copy number in blood is not associated with major depressive disorder in young adults.
abstract: BACKGROUND
  Major depressive disorder (MDD) is the leading cause of disability worldwide, and has significant genetic predisposition. Mitochondria may have a role in MDD and so mitochondrial DNA (mtDNA) has been suggested as a possible biomarker for this disease. We aimed to test whether the mtDNA copy number of peripheral blood leukocytes is related to MDD in young adults.
  
  
  METHODS
  A case-control study was conducted with 210 MDD patients and 217 healthy controls (HC). The mtDNA copy number was measured by quantitative polymerase chain reaction (qPCR) method. Depression severity was assessed by the Hamilton-17 Depression Rating Scale (HDRS-17).
  
  
  RESULTS
  We found no significant differences in mtDNA copy number between MDD patients and HC, though the power analysis showed that our sample size has enough power to detect the difference. There were also no significant correlations between mtDNA copy number and the clinical characteristics (such as age, age of onset, episodes, Hamilton Depression Rating Scale (HDRS) score and Global Assessment of Function Scale (GAF) score) in MDD patients.
  
  
  CONCLUSIONS
  Our study suggests that leukocyte mtDNA copy number is unlikely to contribute to MDD, but it doesn't mean that we can exclude the possibility of involvement of mitochondria in the disease. Further studies are required to elucidate whether mtDNA can be a biomarker of MDD.
authors.affiliation: Institute of Mental Health, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: He
authors.affiliation: Institute of Mental Health, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China.
authors.forename: Jinsong
authors.initials: J
authors.lastname: Tang
authors.affiliation: Institute of Genomic Medicine, Wenzhou Medical University, Wenzhou, Zhejiang, China.
authors.forename: Zongchang
authors.initials: Z
authors.lastname: Li
authors.affiliation: Institute of Mental Health, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.affiliation: Institute of Mental Health, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China.
authors.forename: Yanhui
authors.initials: Y
authors.lastname: Liao
authors.affiliation: Department of Psychiatry, First Affiliated Hospital, China Medical University, Shenyang, Liaoning, China.
authors.forename: Yanqing
authors.initials: Y
authors.lastname: Tang
authors.affiliation: Institute of Mental Health, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China.
authors.forename: Liwen
authors.initials: L
authors.lastname: Tan
authors.affiliation: Institute of Mental Health, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China.
authors.forename: Jindong
authors.initials: J
authors.lastname: Chen
authors.affiliation: The State Key Laboratory of Medical Genetics, Central South University, Changsha, Hunan, China.
authors.forename: Kun
authors.initials: K
authors.lastname: Xia
authors.affiliation: Institute of Mental Health, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China; The State Key Laboratory of Medical Genetics, Central South University, Changsha, Hunan, China; Key Laboratory of Psychiatry and Mental Health of Hunan Province, Central South University, Changsha, Hunan, China; The State Key Laboratory of Medical Genetics, Central South University, Changsha, Hunan, China.
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Chen
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D004272:DNA, Mitochondrial / Q000097:blood* / Q000235:genetics*; D003865:Major Depressive Disorder / Q000097:blood* / Q000235:genetics*; D005260:Female; D018628:Gene Dosage; D006801:Humans; D007962:Leukocytes / Q000378:metabolism*; D008297:Male; D055815:Young Adult
chemical_list: D004272:DNA, Mitochondrial