RÉSUMÉ
BACKGROUND: Cerebral venous sinus thrombosis (CVST) is a rare cause of stroke. Acquired and inherited prothrombotic conditions are the most common risk factors for CVST. Sometimes, an etiology is not found. Wide utilization of next generation sequencing technologies in clinical practice may lead to identification of risk factors other than those classically associated with CVST. METHOD AND RESULTS: This retrospective clinical-laboratory observational study has a reference patient who presented with CVST as an adolescent. Work up for prothrombotic conditions showed high homocysteine level secondary to homozygosity for a common polymorphism, c.677 C > T in the methylenetetrahydrofolate reductase (MTHFR) gene. His older unaffected brother has a similar MTHFR genotype and high homocysteine. The whole exome sequencing revealed a likely pathogenic variant in the sodium voltage gated channel, alpha subunit 1(SCN1A) gene. CONCLUSION: CVST is a multifactorial disease. Prothrombotic conditions are the most common risk factors for CVST. High homocysteine due to the common MTHFR polymorphisms was previously attributed to various thrombotic conditions including CVST. Although high homocysteine due to MTHFR polymorphism may be a contributing factor, additional risk factors such as blood flow abnormalities during SCN1A related seizures may be needed for thrombosis.