In particular, several studies showed that circulating OPN levels are elevated in coronary artery disease (CAD) patients (Abdel-Azeez and Al-Zaky, 2010; Tousoulis et al., 2013; Wolak, 2014; Maniatis et al., 2019) and correlated with the disease extent and severity (Ohmori et al., 2003; Momiyama et al., 2010; Wolak, 2014). This evidence concerns the gene SPP1 and coronary artery disorder.