Zutt et al., in a cohort study of 310 patients [35], stratified into patients with and without PTS, as determined by sonographic and/or phlebographic findings, found that protein S deficiency (P = 0.035) and factor V Leiden (P = 0.003) were significantly more prevalent in the PTS group. This evidence concerns the gene PROS1 and hyperinsulinemic hypoglycemia, familial, 4.