SERPINE1 and hyperinsulinemic hypoglycemia, familial, 4: PAI‐1 deficiency caused by mutations has been reported to lead to a moderate bleeding disorder.1 On the flip side, high levels of PAI‐1 were reported in some families with thrombophilia.2, 3 Blood PAI‐1 antigen levels and activity are strongly correlated and both measures have been used to study the role of PAI‐1 in cardiovascular disease.