Abstract
Objectives: Obsessive compulsive disorder (OCD) is a mental disorder characterized by obsessions and/or compulsions. Impulsive features play a role in the etiology, symptomatology and clinical presentation of OCD. α-synuclein which plays a role in dopaminergic and serotonergic neurotransmission has been shown to be effective in impulse control. The aim of this study is to examine the levels of α-synuclein, serotonin (5-hydroxytryptamine; 5-HT), dopamine, dopamine β-hydroxylase (DBH), 5-hydroxyindolacetic acid (5-HIAA), homovanillic acid (HVA) and heat shock protein 70 (HSP70) in OCD.
Methods: Twenty-six OCD patients and age-gender matched 23 healthy volunteers were included in this study. Biochemical parameters were analyzed by enzyme-linked immunosorbent assay method. Patients were evaluated with Barratt Impulsivity Scale (BIS) and Dimensional Obsession Compulsion Scale (DOCS).
Results: Compared with the controls, significant reduction of 5-HT, dopamine and DBH levels while significant increase of α-synuclein, HVA and HSP70 levels was found in patients with OCD. Moreover, α-synuclein levels were significantly negatively correlated with 5-HT, dopamine and DBH, while significantly positively correlated with HVA, 5-HIAA and HSP70. HTR and dopamine levels were found to be associated with the subscale of BIS. Dopamine and DBH levels were found to be associated with the subscale of DOCS.
Conclusions: It may be suggested that α-synuclein is associated with dopaminergic and serotinergic pathways, and may provide important contributions for elucidating the etiology of OCD. It can be suggested that the effect of dopamine is more than 5-HT, based on the fact that not only dopamine but also DBH is correlated with OCD symptoms.

Key words: Obsessive compulsive disorder, impulsivity, α-synuclein, dopamine, serotonin