[Homozygous (or double heterozygous) antithrombin III defect: AT-III, Budapest 4].
A quantitative-qualitative AT-III deficiency was found in a young woman with severe thromboembolic episodes. Only AT-III molecules with a low heparin affinity were detected in her plasma and these pathological AT-III molecules could not increase the rate of the thrombin-inactivation at all. The pathological AT-III molecules were present in the blood of her father and one of her sisters, but only in a 50% quantity, the other half of the AT-III molecules proved to be functionally normal. The mother of the proposita had deceased earlier, thus she could not be investigated. However, the authors suggest a heterozygous state for her as well, because this assumption can explain the homozygous (or double heterozygous) state of the proposita. In accordance with the convention, this abnormality was designated as AT-III Budapest 4, and the exact biochemical and genetic background of the disorders can be clarified only by further investigations.