The current literature has provided evidence for the relationship between genetic polymorphisms of relevant mediators and AD, and thus far, more than 34 AD-related genic causes have been identified, including FLG, IL-13, RAD50, LRRC32, IL2/IL21, PRR5l, CLEC16A/DEXI, ZNF652, RUNX3, ERBB3, IL6R, CD207, PPP2R3C, IL-7R, STAT3, ZBTB10 and TLR4, etc (1, 16, 17). Here, IL21 is linked to Alzheimer disease.