APOB and syphilis: However, the study28 showed that the serum concentrations of high‐density lipoprotein cholesterol (HDL‐C) and apolipoprotein A‐I (ApoA‐I) were decreased in patients with syphilis compared with those in the syphilitic negative control group, while the concentration of apolipoprotein B (ApoB) was significantly increased in patients with syphilis.