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.
