Claudin-1 is essential for skin barrier function, as evidenced by claudin-1 null mice, which die of dehydration soon after birth and claudin-1 mutations associated with the human disease neonatal ichthyosis-sclerosing cholangitis (NISCH) syndrome [54,55]. This evidence concerns the gene CLDN1 and neonatal ichthyosis-sclerosing cholangitis syndrome.