OBJECTIVETo identify the antithrombin (AT) phenotype and gene mutation of a kindred with hereditary antithrombin deficiency.

METHODSPlasma AT activity and AT antigen level of the propositus and his kindred members were determined with chromogenic substrate method and immunoassay, respectively. All the seven exons and intron-exon boundaries of antithrombin gene were analyzed by PCR and direct sequencing of amplified PCR products from the propositus.

RESULTSThe propositus AT antigen level was normal but his AT activity was only 65% of normal value suggesting that he had type II AT deficiency. A heterozygous G13830A mutation in exon 6 resulting in Arg393His missense mutation in his AT polypeptide was identified in the propositus. The same phenotype and gene mutation were found in other 3 kindred members.

CONCLUSIONThe type II AT deficiency found in this kindred is caused by heterozygous G13830A mutation in AT gene.