<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by hereditary antithrombin deficiency ? [/INST] Hereditary antithrombin deficiency is estimated to occur in about 1 in 2,000 to 3,000 individuals. Of people who have experienced an abnormal blood clot, about 1 in 20 to 200 have hereditary antithrombin deficiency. </s>