Serum concentrations of KLK6 (p = 0.137), CLU (p = 0.178), and ADPN (p = 0.268) did not differ between AD, VAD, MCI and cognitively healthy control group of participants, whereas IL-6 was significantly higher in VAD patients than in AD, MCI, and CHP individuals (p = 0.014). There was no association between investigated biomarkers and clinical patient parameters. The gene discussed is KLK6; the disease is Alzheimer disease.