Materials and Methods Subjects Thirty-three patients meeting DSM-IV-TR criteria for OCD (American Psychiatric Association 2000) were consecutively approached from the IRCCS Santa Lucia Foundation in Rome. Diagnosis of OCD was made by a senior research psychiatrist (G. S.)

who was also the clinician in charge of the patients’ treatment, acquainted with their clinical history. All diagnoses were confirmed using the Inhibitors,research,lifescience,medical Structured Clinical Interview for DSM-IV-TR (SCID)-Patient Edition (First et al. 2002a). Clinical history was collected from patients’ check details physician or psychiatrist and clinical charts and eventually supplemented by interviewing the patients and their relatives. Symptom severity was assessed by a senior psychologist, Inhibitors,research,lifescience,medical PhD level, using the 10-item clinician-rated Yale-Brown Obsessive Compulsive Scale (Y-BOCS) (Goodman et al. 1989). Patients were also screened for the presence of general anxiety and depressive symptoms through the administration of the Hamilton Anxiety Rating Scale (HAM-A, Hamilton 1959) and the Hamilton Depression Rating Scale (HAM-D, Hamilton 1960). Exclusion criteria included:

(1) comorbid psychiatric disorders according to DSM-IV-TR criteria, (2) a history of psychoactive substance dependence or abuse during lifetime, (3) a history of neurologic illness or brain injury, (4) major medical illnesses, that is, diabetes not stabilized, obstructive pulmonary disease Inhibitors,research,lifescience,medical or asthma, hematological/oncological disorders, B12 or folate deficiency as evidenced by blood concentrations Inhibitors,research,lifescience,medical below the lower normal limit, pernicious anemia, clinically significant and unstable active gastrointestinal, renal, hepatic, endocrine or cardiovascular system disease, newly treated hypothyroidism, (5) the presence of any brain pathology as instantiated by standard magnetic resonance imaging (MRI) exams (including T1, T2 and FLAIR protocols). In particular, the presence, severity and location of vascular lesions were rated according to a protocol designed for the Rotterdam Scan Study (de Leeuw

et al. 2001). They are Inhibitors,research,lifescience,medical considered present in cases of hyperintense lesions on both proton-density and T2-weighted and were rated semiquantitatively as Dichloromethane dehalogenase 0 (none), 1 (pencil- thin lining), 2 (smooth halo) or 3 (large confluent) for three separate regions; adjacent to frontal horns (frontal caps), adjacent to the wall of the lateral ventricles (bands) and adjacent to the occipital horns (occipital caps). The total vascular lesion load was calculated by adding the region-specific scores (range, 0–9). In this study, only patients rated 0 were included, (6) global cognitive deterioration according to a Mini-Mental State Examination (MMSE) (Folstein et al. 1975) score lower than 26, (7) premorbid IQ below the normal range according to TIB (Test Intelligenza Breve, Italian analog of the National Adult Reading Test – NART – Nelson 1982) cutoff score of 93.1 (Sartori et al.