To gain further insight into the role of TJs and Cldn-1 in epidermal dysfunction in AD, we determined Cldn-1 levels in healthy as well as lesional and non-lesional skin from AD patients and correlated the results to TJ barrier function identified by inside-out permeation of Biotin-556 (“Biotinylation assay”2,4,5) and overall epidermal barrier function measured by TEWL. This evidence concerns the gene CLDN1 and Alzheimer disease.