MTHFR and venous thromboembolism: Additionally, the presence of a methylenetetrahydrofolate reductase (MTHFR) gene mutation adds further complexity. Congenital IVC atresia and MTHFR gene mutations are individually recognized risk factors for venous thromboembolism; however, their coexistence is exceedingly rare, with only a few cases reported in the literature, primarily in young adults presenting with extensive or bilateral DVT [5].