Within the population at large, there are at least 2 groups of inherited thrombophilias based on prevalence; those with a higher prevalence, 3% to 11% (FV G1691A and FII G20210A) and those with a lower prevalence, < 1% (protein C, protein S, and antithrombin deficiency). Diagnosis of a child with venous thromboembolism can be used to identify first-degree relatives with inherited thrombophilia who are at increased risk of venous thromboembolism; most notably protein C, protein S, and antithrombin deficiency, and to a much lesser extent FV G1691A and FII G20210A. PC indicates protein C deficiency; PS, protein S deficiency; AT, antithrombin deficiency; VTE, venous thromboembolism; IT, inherited thrombophilia; and combined IT, combined inherited thrombophilia (rare). See also Figure 2 in the article by Holzhauer et al that begins on page 1510.¹  Professional illustration by Marie Dauenheimer.