Harlequin ichthyosis (HI) is a rare and severe form of ichthyosis and is characterized by thickened. hard. armor-like plates of skin that cover the entire body. This disease is caused by mutations in the adenosine triphosphate-binding cassette transporter protein A12 gene. https://www.roneverhart.com/Under-Armour-Hustle-5-0-TEAM-Backpack/