In this sense, one study concluded that the combination of four serum biomarkers, which are thymus and activation-regulated chemokine (TARC)/CC chemokine ligand 17 (CCL17), pulmonary and activation-regulated chemokine (PARC)/CCL18, interleukin (IL)-22, and sIL-2R, were better correlated with AD severity than individual biomarkers [13], although TARC/CCL17 alone may also be a good marker [14]. This evidence concerns the gene CCL18 and Alzheimer disease.