Increased Serum Levels of α-Synuclein in Patients With Major Depressive Disorder

Objective: Epidemiologic studies have demonstrated that depression is a risk factor for dementia. In particular, dementia with Lewy bodies (DLB) has been noted to be highly relevant to depression. It has been suggested that alpha-synuclein (alpha-syn), a major component of Lewy bodies, is related to the onset and progression of DLB. To investigate the relationship between depression and DLB, we compared serum alpha-syn levels of patients with depression to those of healthy subjects. Methods: The subjects were 103 inpatients with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), or DSM-5 major depressive disorder (MDD) and 132 healthy comparisons. Patients were recruited from Juntendo Koshigaya Hospital, Saitama, Japan, between June 2010 and November 2016. Serum alpha-syn levels were measured using an enzyme-linked immunosorbent assay kit. Serum alpha-syn levels were compared using a 2 (age group [< 60 years versus = 60 years])x 2 (diagnosis [MDD versus comparison]) analysis of variance. Results: There was no significant main effect of age (F = 1.167, df = 1, 231, p = 0.281). There was a significant main effect of diagnosis (F = 44.657, df = 1, 231, p < 0.001), with higher alpha-syn levels in the MDD group versus the healthy comparison group, regardless of age. Conclusion: The present results suggest that depression may affect the metabolism of alpha-syn; there is a possibility that depression is not only a prodromal symptom of DLB but also a causal risk factor for DLB.