While syndecan-1 and endocan showed no relationship with plasma lipid concentrations, there were weak associations between follow-up syndecan-1 and interleukin-1-beta (R<sup>2</sup> = 0.21, P = 0.001), and follow-up endocan and interleukin-6 (R<sup>2</sup> = 0.15, P = 0.008).<h4>Conclusions</h4>Although serum syndecan-1 and endocan levels decreased in peripheral blood over time post-MI on guideline-directed therapy, this study identified only modest relationships between syndecan-1 (and not endocan) and OCT compositional characteristics of lipid-rich, rupture-prone plaque. The gene discussed is SDC1; the disease is myocardial infarction.