SERPINE1 p.Val17Ile was detected only in one CTEPH patient (P7), whose PAI-1 antigen concentration was below the lower limit of the reference interval (4.1 ng/mL, reference interval 7–43 ng/mL), rather characteristic of a mild PAI-1 deficiency. Here, SERPINE1 is linked to hyperinsulinemic hypoglycemia, familial, 4.