ORGANS AFFECTED
SKIN
The skin is the primary organ that is affected in people with Harlequin ichthyosis. People with this condition are born with hard, tight, and thick skin that cracks and splits apart (refer to the image above), leaving them highly susceptible to skin infections. Since their skin also prevents normal heat loss and water retention, people with Harlequin ichthyosis also have very dry skin, are very sensitive to changes in external and internal temperatures and are often dehydrated.
EYES
Harlequin ichthyosis also affects the eyes. When an infant with the disorder is born, the tightness of the skin will pull around the eyes, forcing the eyelids to turn inside out (refer to the image above of a newborn's eyes with the disorder), making the person unable to blink and a chance that their eyes would be infected. This will cause the eyes to become extremely dry and allow the cornea to become damaged, leaving the person with very poor vision if they do not take measures (such as using eye drops) to lubricate and protect the cornea.
EARS
People with Harlequin ichthyosis can be born with ears that appear to be misshapen or missing due to the ears being fused to the head by the thick skin (refer to the image above). Along with the extra skin that can build up over the outer ear and the outside of the ear canal, this can lead to the person to have trouble hearing.
BLOOD
Due to the skin being unable to retain a lot of water, people with Harlequin ichthyosis will have hypernatremia (high amounts of sodium in their blood), This can lead to a build-up of plaque in the arteries, which can cause high blood pressure and can be fatal if not managed (refer to the image above for a series of diagrams that can occur in the arteries if the sodium level in the blood is too high).
ORGAN SYSTEMS AFFECTED
INTEGUMENTARY SYSTEM
This is the primary organ system (refer to the 3D image to the right) that is affected in people with Harlequin ichthyosis. The thick, hard, and cracked epidermal layer of the skin prevents hair follicles from growing, leaving people with scarce hair. The skin also prevents sweat from the sweat glands to reach the surface of the skin. This means that it is harder for people with Harlequin ichthyosis to retain and adjust their body temperature.
RESPIRATORY SYSTEM
The respiratory system (refer to the 3D image to the right) is also affected. People with Harlequin ichthyosis usually have trouble breathing from their skin being extremely tight, sometimes leading to hypoventilation and respiratory failure. This is due to the underdeveloped lungs, the intercoastal muscles and the thoracic cage being unable to expand and draw in enough air by the restriction of tight skin when inhaling.
SKELETAL SYSTEM
People with Harlequin ichthyosis might have underdeveloped bones (called hypoplasia), leaving their limbs, such as arms, fingers, and legs being smaller than the normal size, represented by the 3D image of the skeletal system to the right. Their joints can also be lacking in movement due to the extreme inelasticity of the skin.
CAUSES OF HARLEQUIN ICHTHYOSIS AND HOW IT AFFECTS THE BODY
Harlequin ichthyosis is a genetic condition that is passed on through a mutation in the ABCA12 gene. The ABCA12 gene provides instructions for making a protein that is essential for the normal development of skin cells in the epidermis. This protein plays a major role in the transport of lipids in the epidermis, which is needed for thermal regulation, protection, and preventing infection. Some mutations in the gene can prevent the cell from making any ABCA12 protein at all, while others lead to the production of an abnormally small version of the protein that cannot transport lipids properly.
Since lipids are essential for the normal development of skin, the inadequate lipid transport system prevents the skin from forming an effective barrier. This disrupts the normal development of the epidermis, resulting in the skin becoming hard, thick and tight in Harlequin ichthyosis. This creates deep fissures in the skin that leaves the body vulnerable to infection, as well as having difficulty to move and breathe. Since the body requires extra calories to create skin and maintain the body's normal function, physical development can be delayed as well.
Someone can inherit the autosomal recessive gene mutation from one parent and not have the disorder, but, like their parents, they can pass it down to their children. However, if someone inherits the mutated gene from both parents, they will have the disorder.
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When both parents are carriers of the gene, there is a 25% chance that their biological child will also have the condition. The risk is the same regardless of the child's gender. Harlequin ichthyosis affects about 1 in 500, 000 people.
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Someone can test if they are a carrier of the gene without having the disorder by taking a series of genetic tests using samples of their skin, hair and blood.
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Click on the diagrams below to find out more about the ABCA12 gene and how its mutation causes the skin to become extremely dry, scaly, and thick, which is a prominent symptom in people with Harlequin ichthyosis.
A diagram of the different layers of healthy skin with the normal functioning ABCA12 gene.
A diagram of the different layers of skin of a person with Harlequin ichthyosis. Due to the mutation in the ABCA12 gene, lipids are not able to be produced, causing in the extra layers of hardened skin.
A diagram of the different layers of healthy skin with the normal functioning ABCA12 gene.
When both parents are carriers of the ABCA12 mutation gene, there is a 25% chance that their child will have Harlequin ichthyosis, a 50% chance that their child would be a carrier of the mutation and a 25% chance that their child would have no mutation of the gene at all (refer to the diagram below).
