Proprotein convertase subtilisin/kexin type 9 (PCSK9) reduces the uptake of low density lipoprotein (LDL) cholesterol by increasing the endosomal and lysosomal degradation of LDL receptor, accompanied by an increase in circulating LDL [45]. PCSK9 has been considered as a promising target for lipid-lowering therapy [6]. Recently, several studies showed the new role of PCSK9 in the pathogenesis of ACS and suggested a potential parameter for decision-making in ACS [789].

In this article entitled "Serum levels of PCSK9 are associated with coronary angiographic severity in patients with acute coronary syndrome," Bae et al. [10] evaluated whether a high level of serum PCSK9 is associated with a high risk and severity of ACS. They showed that serum PCSK9 levels were positively associated with the proportion of patients with coronary angiography lesions after adjustment for multiple variables, suggesting that PCSK9 is a potential biomarker of the severity of coronary artery disease. The authors have clearly showed their results in this manuscript, and this approach is quite valuable and helpful to establish a method for early identification and individual strategies of ACS.

However, these results may not be generalizable to all patients because only male participants were enrolled. I hope for a large multicentre prospective cohort study including both genders, especially considering the menopausal state. I also expect to extend the study to see whether there is an association between the level of PCSK9 and prognosis such as recurrence rate and mortality. Lastly, it would have more valuable if they could compare PCSK9 and other biomarkers of ACS, as the authors mentioned.