There are very limited studies on the use of OPG as an index of endothelial dysfunction in adult patients with T1DM or T2DM [11–14], while there is only one previous study on OPG in T1DM children and adolescents, which, however, is associated only with their bone status [12], and not with endothelial dysfunction. The gene discussed is TNFRSF11B; the disease is type 2 diabetes mellitus.