ABCA12 and Harlequin ichthyosis: Interestingly, some of these genes, i.e. KRT1, KRT9, KRT16, DSG1, DSC2 and JUP, are mutated in hereditary PPKs [16, 17], while the ABCA12 gene is defective in harlequin ichthyosis characterized by the loss of the skin lipid barrier [46].