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Updated: Jun 22, 2026

Protocol for Repetitive Transcranial Magnetic Stimulation with Symptom Provocation to Treat Obsessive-compulsive Disorder
Published on: November 25, 2025
Treatment of monozygotic twins with obsessive compulsive disorder using cognitive therapy and exposure with ritual
Michael P Twohig1, Maureen L Whittal, Katherine A Peterson
1Utah State University, Logan, UT 84322, USA. michael.twohig@usu.edu
Background:
Assessment and treatment of cohabiting monozygotic (MZ) twins with obsessive compulsive disorder (OCD) is a possible challenge for clinical psychologists.
Aims:
This study aims to present a detailed history of two sets of cohabiting MZ twins with OCD, and describe the adaption of cognitive behavior therapy in their treatments.
Method:
Two sets of cohabiting MZ twins completed a structured intake and the Yale Brown Obsessive Compulsive Scale as well as measures of depression, anxiety, a measure of obsessive beliefs, and thought action fusion. One set received cognitive behavior therapy and exposure with ritual prevention (ERP) simultaneously and the other received ERP separately. Pre-, post-treatment and follow-up assessments occurred for both sets of twins.
Results:
All four individuals showed notable decreases in OCD, and results were maintained for three of the four participants at follow-up points.
Conclusions:
This study highlights the developmental course of OCD that can occur in cohabiting twins, and the clinical adaption that may be necessary.
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