RESUMO
BACKGROUND: Atresia of the infrarenal inferior vena cava (IVC) is associated with thrombophilia and antithrombin (AT) deficiency (ATD) due to homozygosity for the so-called Budapest 3 variant, c.391C > T, in the gene, SERPINC1. CASE PRESENTATION: We report on a father and his two sons that had severe thrombosis at a young age. One son had absence of, and the other had very gracile infrarenal IVC. The father had gracile vena iliaca. All had significant collateral building. AT activity was determined with four different methods and varied between moderately reduced and borderline normal values, depending on the method. While all were heterozygous for c.391C > T, the father was also heterozygous for a variant of uncertain significance in SERPINC1. CONCLUSIONS: The findings support the association between c.391C > T in SERPINC1, thrombophilia, and atresia of the IVC system and indicate that even heterozygosity for c.391C > T may contribute to such anomalies. ATD detection was hampered by the varying sensitivity of methods used for AT activity measurement.