CLDN1 and Alzheimer disease: Additionally, in a CLDN1 knock-down (KD) in vitro 3D model of a reconstructed human epidermis that expressed different levels of CLDN1, intercellular lipid lamellae length was significantly reduced after CLDN1 KD at day 8, with a significant downregulation of filaggrin mRNA (a protein produced by keratinocytes which have been linked to several allergic diseases including AD) (Nomura et al., 2008; Thyssen and Kezic, 2014; Bergmann et al., 2020).