RPTN and Alzheimer disease: One of the possible explanations of this inconsistency is that AD risk alleles indeed increase the CRNN gene expression in the healthy skin in some way, but this effect becomes opposite in the AD-like skin due to the significantly modified expression of the other cornified envelope proteins (FLG, FLG2, LOR, CRNN, SPRR3v1, RPTN, HRNR, SPRR1Av1) [68].