Harlequin type ichthyosis (also harlequin ichthyosis, ichthyosis congenita, or keratosis diffusa fetalis), the most severe form of congenital ichthyosis, is characterized by a thickening of the keratin layer in fetal human skin, appearing as massive, diamond-shaped scales. In addition, the eyes, ears, mouth, and other appendages may be abnormally contracted. The scaly keratin limits the child's movement, and because it is cracked where normal skin would fold, it is easily pregnable by bacteria and other contaminants, resulting in a serious risk of fatal infection.
Sufferers are known as harlequin fetuses, harlequin babies, or harlequins.
The harlequin type designation comes from both the baby's apparent facial expression and the diamond-shape of the scales (resembling the costume of Arlecchino), which are caused by severe hyperkeratosis. Seventeenth century entertainers known as jesters, or harlequins, wore costumes with diamond patterns on them, as well as a particular style of face paint. The features of the harlequin fetus resemble this stylized makeup, and their faces are often pulled tight into grim parodies of a clown's smile. The disease can be diagnosed in the womb by way of fetal skin biopsy.




