ANTITHROMBIN-III KUMAMOTO-II - A SINGLE MUTATION AT ARG393-HIS INCREASED THE AFFINITY OF ANTITHROMBIN-III FOR HEPARIN

Abnormal antithrombin III (AT III) was found in a 30-year-old woman wh o suffered from recurrent thrombosis during pregnancy and the postpart um period. Among her family members, only her father had recurrent epi sodes of deep vein thrombosis of the lower extremities, from his youth . The antithrombin and antifactor Xa heparin cofactor activities of th e proposita's plasma were 61% and 42% of normal, respectively. The pro gressive antithrombin and antifactor Xa activities were also decreased to 55% and 58% of normal, respectively. The immunoreactive level of A T III was within the normal range (23.1 mg/dl). Analysis of the propos ita's plasma by crossed immunoelectrophoresis in the presence or absen ce of heparin and by affinity chromatography on heparin-Sepharose reve aled that the proposita's AT III had apparently normal affinity for he parin. Nucleotide sequencing of 7 exons of the proposita's AT III gene amplified by polymerase chain reaction (PCR) disclosed that the secon d base of codon 393 comprised both G and A, indicating Arg393-His conv ersion. The base sequences of exons 1, 2, 3a, 3b, 4, and 5 were normal , excluding any other mutation. These findings indicated that the prop osita's AT III was a variant of AT III at the thrombin binding site an d that the proposita was a heterozygote for the abnormality. Heparin a ffinity of purified abnormal AT III from the proposita's plasma was de monstrated to be increased upon affinity chromatography using heparin- Sepharose, suggesting that the mutation (Arg393-His) per se could poss ibly increase the affinity of antithrombin III for heparin. For this v ariant AT III (Arg393-His), the name AT III Kumamoto II is proposed. ( C) 1995 Wiley-Liss, Inc.