Harlequin Ichthyosis is the most dramatic of the congenital ichthyoses. At birth, the infants display a profound thickening of the skin and as a result are encased in a massive thickened shell of abnormal skin. They also have contractions of the eyes, mouth, limbs and have an abnormal barrier function, leading to fluid shifts, metabolic abnormalities and susceptibility to infections. Those of you who have children should thank your maker every day your child does not suffer from this condition.
It, like many of the ichthyoses, is an autosomal recessive condition, and the specific genetic abnormality is ABCA12 on chromosome 2. They have ultrastructural abnormalities related to the formation of and maturation of keratin. Although this was at one time always fatal, with the advent of treatment with systemic retinoids there are multiple reported survivors.
As a bonus question, clinically how could you differentiate between lamellar ichthyosis and harlequin ichthyosis?