Most AT3D manifestation belong to the type I deficiency group with a severe plasma deficiency of AT3; in type II (functional) deficiency, these subjects possess normal AT3 serum levels, but mutations in functional domains of this anticoagulant—including the RCL, the heparin-binding site (HBS), or the A- and C-sheet domain—impair or abolish inhibitory activity [50–53]. Here, SERPINC1 is linked to hyperinsulinemic hypoglycemia, familial, 4.