title: Significantly lower nerve growth factor levels in patients with major depressive disorder than in healthy subjects: a meta-analysis and systematic review.
abstract: BACKGROUND
  Since its discovery several decades ago, nerve growth factor (NGF) has been found to play roles in different areas, such as neurology, endocrinology, and immunology. There is some evidence linking NGF and psychiatry, including the role of NGF in subjects' response to stress, the alteration of NGF in different emotional states, and the penetration of NGF across the blood-brain barrier under specific conditions. There are many inconsistent findings regarding the differences in NGF in patients with major depressive disorder (MDD) at the present time. The aim of our study was to clarify whether NGF levels are different in MDD compared with healthy controls (HCs).
  
  
  METHODS
  We conducted a thorough literature search and compared peripheral NGF levels between MDD and HC through meta-analysis, and investigated possible confounding variables through meta-regression.
  
  
  RESULTS
  Seven studies were brought into the current meta-analysis comparing peripheral NGF in MDD and HCs. The main result was that the NGF levels were significantly lower in MDD than in HCs and that this had an inverse correlation with mean age and disease severity. In addition, meta-analysis of four articles found that the peripheral NGF levels did not change significantly before and after treatment.
  
  
  CONCLUSIONS
  Our study highlights the significant differences in peripheral NGF levels in patients with MDD. However, further exploration of the dynamic changes in peripheral NGF along with the disease course, and specific studies investigating the correlation of NGF in the peripheral and CNS environments are still needed.
authors.affiliation: Department of Neurology, E-Da Hospital, Kaohsiung, Taiwan.
authors.forename: Yen-Wen
authors.initials: YW
authors.lastname: Chen
authors.affiliation: Department of Psychiatry, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan ; Center for Translational Research in Biomedical Sciences, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung, Taiwan.
authors.forename: Pao-Yen
authors.initials: PY
authors.lastname: Lin
authors.affiliation: Department of Psychiatry, Tsyr-Huey Mental Hospital, Kaohsiung Jen-Ai's Home, Kaohsiung, Taiwan.
authors.forename: Kun-Yu
authors.initials: KY
authors.lastname: Tu
authors.affiliation: Department of Psychiatry, Tsyr-Huey Mental Hospital, Kaohsiung Jen-Ai's Home, Kaohsiung, Taiwan.
authors.forename: Yu-Shian
authors.initials: YS
authors.lastname: Cheng
authors.affiliation: Department of Psychiatry, Tsyr-Huey Mental Hospital, Kaohsiung Jen-Ai's Home, Kaohsiung, Taiwan.
authors.forename: Ching-Kuan
authors.initials: CK
authors.lastname: Wu
authors.affiliation: Department of Psychiatry, Tsyr-Huey Mental Hospital, Kaohsiung Jen-Ai's Home, Kaohsiung, Taiwan.
authors.forename: Ping-Tao
authors.initials: PT
authors.lastname: Tseng
keywords: NGF; mood disorder; neurotrophic factor; psychiatry