HOMOZYGOUS OR COMPOUND HETEROZYGOUS QUALITATIVE ANTITHROMBIN-III DEFICIENCY

A male patient of 24 years who had experienced thrombotic episodes sin ce the age of is displayed art unusually low antithrombin III (AT III) activity measured as heparin cofactor (13% of the normal), while a si milarly decreased value (16% of normal) was found in a 26 year old bro ther who had suffered from thrombotic events since the age of 12 years . AT III heparin cofactor activities were close to 50% of normal in th e father, mother, another brother and a sister, none of whom had exper ienced thrombotic episodes. Since all available members of the family, including the patient displayed near normal AT III antigen levels (73 -85%) normal total progressive antithrombin activities (92-110%) as as sessed by the thrombin agarose diffusion technique and normal total pr ogressive anti-Xa activities, the propositus and his brother could be considered to be homozygotes or compound heterozygotes for a qualitati ve familial AT m deficiency probably caused by an abnormality of the h eparin binding site. Molecular techniques would be required to elucida te the precise mutation giving rise to the deficiency.