Serotonin transporter binding is increased in Tourette syndrome with Obsessive Compulsive Disorder

Area of Science:

• Neuroscience
• Psychiatry
• Pharmacology

Background:

• The serotonergic system's role in obsessive-compulsive disorder (OCD) is known, but its function in Tourette syndrome (TS) remains unclear.
• Previous studies suggested decreased serotonin transporter (SERT) binding in TS patients with comorbid OCD (TS+OCD).

Purpose of the Study:

• To investigate SERT binding in TS patients with and without OCD (TS-OCD) compared to healthy controls (HC) and OCD patients.
• To examine the influence of escitalopram treatment on SERT binding in TS+OCD and OCD patients.

Main Methods:

• Utilized the SERT imaging ligand [¹²³I]2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine ([¹²³I]ADAM) and single-photon emission tomography (SPECT).
• Included 33 adult subjects: 10 HC, 10 TS-OCD, 8 TS+OCD, and 5 OCD.
• SPECT scans were repeated after 12-16 weeks of escitalopram treatment in OCD and TS+OCD patients.

Main Results:

• SERT binding was normal in OCD and TS-OCD patients compared to HC.
• Significantly increased SERT binding was observed in TS+OCD patients, particularly in the caudate and midbrain, compared to HC and TS-OCD.
• Escitalopram treatment led to a significant reduction in SERT binding (19-79%) but showed no correlation with clinical improvement.

Conclusions:

• Altered serotonergic system function in TS appears linked to comorbid OCD, not the primary cause of TS itself.
• Increased SERT binding in TS+OCD suggests a specific neurobiological mechanism related to the comorbidity.