How do Genes Cause Harlequin Ichthyosis

Harlequin ichthyosis is a severe genetic disorder that mainly affects the skin. Infants with this condition are born with very hard, thick skin covering most of their bodies. The skin forms large, diamond-shaped plates that are separated by deep cracks (fissures).

Affected babies are born prematurely and small for dates. The skin is covered in tight, thick, plates of hard scale and resembles armour plating or the harlequin suit of a jester. It splits at several areas causing deep cracks. The face looks stretched with turned out lips and eyelids, and the ears, hands and feet may be hidden in the scale. The eyes may be invisible because they are temporarily covered by the swollen eyelids. The baby’s movement and ability to suck is affected and they suffer all the problems of leaky skin.

They become dehydrated and have poor temperature control, difficulty feeding and sometimes breathing and are also at risk of serious infection.

How do Genes Cause Harlequin Ichthyosis

Harlequin ichthyosis comes out of the blue. The parents of an affected baby are carriers and will have a one in four risk of any future baby of theirs being similarly affected. This is another genetic disease due to a single important skin gene being faulty or mutated.

In this case, the mutation is in ABCA12, a gene thought to be involved in transport of lipids (fats) into the spaces between the cells in the skin's uppermost layer. These lipids act as a protective barrier against bacteria and infection.

The ABCA12 gene provides instructions for making a protein that is essential for the normal development of skin cells. This protein plays a major role in the transport of fats (lipids) in the outermost layer of skin (the epidermis).

Some mutations in the ABCA12 gene prevent the cell from making any ABCA12 protein. Other mutations lead to the production of an abnormally small version of the protein that cannot transport lipids properly. A loss of functional ABCA12 protein disrupts the normal development of the epidermis, resulting in the hard, thick scales characteristic of harlequin ichthyosis.

How do People Inherit Harlequin Ichthyosis?

National Institute of Health explains that this condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

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