Fig. 1

Genomic test results for patients in diagnostic and screening contexts. a Patients in scenario 1, in which genomic testing is used for diagnosis to support clinical signs that suggest Marfan syndrome. The overlapping circles represent the relative likelihood or probabilities for the scenario. The blue circle is all patients who have clinical signs that cause their doctors to request genomic tests. The 75% of these patients who actually have Marfan syndrome are the dark orange circle and patients with a pathogenic variant are the lighter orange circle. The small green sliver on the right are the patients who do not have the disorder but have a false-positive test—a pathogenic variant that isn’t actually causative. b In scenario 2, in which genomic testing is used for screening of patients without clinical signs of Marfan syndrome, the green area is still relatively small compared to the blue circle, because the false-positive rate is unchanged. What have changed dramatically are the dark orange circle (because the presence of the disorder is less likely in a screening scenario) and the ratio of the green area to the light orange area: in this case, a false-positive test is more likely than a correct diagnosis of Marfan syndrome