DSG4 and psoriasis: Several genes associated with skin-related disorders such as peeling skin syndrome (TGM5), hypotrichosis (loss or reduction of hair, DSG4), ichthyosis (thickened and scaly skin, ALOXE3) or psoriasis (KLK8) are lost in aquatic mammals that exhibit a much thicker epidermis, a high shedding rate of epidermal cells and hair loss (18,52).