Harlequin ichthyosis: a very rare, severe inherited (genetic) disorder that results in hard, thick skin that forms diamond-shaped plates that are separated by cracks or fissures. Affected infants often develop dehydration and life-threatening infections in the first weeks of life, due to lack of function of the skin as a protective barrier. Harlequin ichthyosis is caused by mutations in the ABCD12 gene and is inherited in an autosomal recessive manner, meaning an affected person must receive one defective copy of the gene from each parent.
REFERENCE: Genetics Home Reference. "Harlequin ichthyosis." Nov 2008