1. Albinism. In this anomaly the skin and hair lack melanin pigment. It is an error of metabolism caused by a lack of the enzyme tyrosinase. It is a hereditary disorder (autosomal recessive).
2. Nevus. This term is used to denote either a pigmented spot (called a mole) or to a red or purple discoloration of skin (called a birthmark). The birthmarks are caused by abnormal vascular plexuses (called hemangiomas) which are located in the dermis.
3. Icthyosis. This is a congenital anomaly resulting from excessive keratini-zation of superficial layers of the epidermis. The main features of this anomaly are dryness and scaliness of skin.