Background and Clinical Significance: Herein, we describe the clinical case of a 17-year-old patient with psychotic disorder secondary to cerebral venous thrombosis due to primary thrombophilia, which was related to protein S deficiency and a heterozygous MTHFR gene mutation with the p.Ala222Val variant. Case presentation: A 17-year-old female, with no history of previous illnesses, was admitted to the emergency service department due to a psychotic break. Psychiatric evaluation detected disorganized thought, euphoria, ideas that were fleeting and loosely associated, psychomotor excitement, and deviant judgment. On the fifth day, an inflammatory process in the parotid gland was detected, pointing out a probable viral meningoencephalitis, prompting antiviral and antimicrobial treatment. One week after antiviral and steroidal anti-inflammatory treatments, the symptoms’ improvement was minimal, which led to further neurological workup. MRI venography revealed a filling defect in the transverse sinus, consistent with cerebral venous thrombosis. Consequently, anticoagulation treatment with enoxaparin was initiated. The patient’s behavior improved, revealing that the encephalopathic symptoms were secondary to thrombosis of the venous sinus. Hematological studies indicated the cause of the venous sinus thrombosis was a primary thrombophilia caused by a heterozygous MTHFR mutation variant p.Ala222Val and a 35% decrease in plasmatic protein S. Conclusions: This case highlights the possible relationship between psychiatric and thrombotic disorders, suggesting that both the MTHFR mutation and protein S deficiency could lead to psychotic disorders. Early detection of thrombotic risk factors in early-onset psychiatric disorders is essential for the comprehensive management of patients.

Background and Clinical Significance: Herein we describe the clinical case of a 17-year-old patient with psychotic disorder due to primary thrombophilia, which was re-lated to protein S deficiency and P.ALA22VAL variant MTHFR gene mutation. Case presentation: A 17-year-old female, with no history of previous illnesses, was admitted to the emergency service due to a psychotic break. Psychiatric evaluation detected disor-ganized thought, euphoria, ideas that were fleeting and loosely associated, psychomotor excitement, and deviant judgment. On the fifth day, an inflammatory process in the pa-rotid gland was detected, pointing out a probable viral meningoencephalitis. An antiviral and antimicrobial treatment was immediately given. One week after antiviral and steroi-dal anti-inflammatory treatments, the symptoms improvement was minimal, leading to a presumptive diagnosis of an encephalopathic syndrome. Given the suspicion of a vascu-lar event, a venous MRI was performed, showing a filling defect in the transverse sinus; consequently, anticoagulation treatment with enoxaparin was initiated. The patient´s be-havior improved, revealing that the encephalopathic symptoms were secondary to thrombosis of the venous sinus. Hematological studies were performed to rule out prima-ry coagulopathy and primary thrombophilia; these studies demonstrated a MTHFR mu-tation variant P.ALA22VAL and a 35% decrease in plasmatic Protein S. Conclusion, this case highlights the feasible relationship between psychiatric and hematological disorders, underlining the importance of the MTHFR mutation and protein S deficiency in the de-velopment and progression of psychotic disorders. Early detection of these factors is es-sential for comprehensive management in patients with onset of atypical psychiatric illnesses.