SPINK5 and Alzheimer disease: Kallikrein-related peptidase (KLK) genes, such as KLK5, KLK14, and lipid metabolism gene ELOVL1, were down-regulated in AD skin (29), while protease inhibitor SPINK5 (serine protease inhibitor of kazal type 5) and human aquaporin 3 (AQP3) were up-regulated, which function in elevating inflammatory responses and epidermal water loss, respectively (29, 91).