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Type 2 Antithrombin Deficiency: Dr. Stephan Moll, UNC

George, I noted your new website-blog. Interesting activity. I will challenge you with a question:

33 year old woman with type 2 antithrombin deficiency (AT activity – chromogenic Xa inactivation assay in the presence of heparin – HemosIL Liquid Antithrombin) is 58 % (normal 88 and above) twice, from from 2 separate blood draws. AT antigen level is normal at 110 % (nl 82 – 133)
Mother has similar AT activity and antigen levels.
Dx of inherited type 2 AT deficiency is made.
Patient had an arterial clot with birth control pill at age 29.
As mother has never had a blood clot, in spite of 2 C-section deliveries, several other surgeries, and being on HRT for many years, I wonder whether this family has type 2b AT deficiency, i.e. a defect in the heparin binding region, which is said to be less thrombogenic than type 1 or type 2a (defect in antithrombin’s active site).
What test can I do to verify my suspicion of a type 2b defect?
Who in the U.S. does an AT activity assay in the absence or with only low concentration of heparin?
Are there other options to make a diagnosis of 2b?
Who does sequencing of the AT gene, i.e. where do I send the sample to? What does it cost?
Hope you are well.
Best regards, Stephan

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