Objective: To identify the antithrombin (AT) phenotype and gene mutation of a kindred with hereditary antithrombin deficiency.
Methods: Plasma 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.
Results: The 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.
Conclusion: The type II AT deficiency found in this kindred is caused by heterozygous G13830A mutation in AT gene.