What is Harlequin Ichthyosis?
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Harlequin ichthyosis (HI) is the most severe form of congenital dry skin disorders [1]. The epidermis of affected individuals does not form properly, partially due to impaired lipid transport. Skin cannot act as a protective barrier between the person and the environment.
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Figure 1. Early illustration of
harlequin ichthyosis in a newborn (circa 1886) |
SymptomsInfants born with HI have thickened parchment colored skin over the entirety of their bodies, separated by fissures into keratin plates [2]. Sufferers exhibit severe deformities to the head and face. The ears, nose, and eyelids may be extremely underdeveloped or missing entirely. The lips and eyelids are often pulled back by dry skin or inverted [1]. Infants often bleed during birth. HI patients are extremely sensitive to changes in temperature, dehydration, and infection [2].
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Figure 2. Photo of a newborn baby suffering from harlequin ichthyosis
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Inheritance
HI is a rare autosomal recessive disease affecting one in 300,000 births Males and females are equally affected. An individual must have two copies of the mutant ABCA12 to have the disease. If only one mutant is present, that person is a carrier of the disease but does not express its symptoms. If two carriers of HI choose to reproduce, they both have the possibility of passing on one ABCA12 allele a normal or mutant. The children have a 25% chance of inheriting both mutant alleles and suffering from HI. There is a 50% chance they will inherit one mutant copy, and be carriers of the disease. The remaining 25% likelihood will be no inheritance of either mutant allele.
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Diagnosis
Although visible symptoms are often the initial indicator of HI, prenatal and postnatal genetic testing may also be preformed. DNA can be obtained from the fetus or infant and tested for a loss of function mutation in the ABCA12 gene [3].
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TreatmentThere is no cure for HI, and infants often die within the first few weeks of life. However, with intensive medical care survival is possible. Oral retinoid therapy can soften scales and discourage dehydration. Children who survive the neonatal period often evolve to have a less severe disease phenotype.
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Gene and Protein Function
Harlequin ichthyosis is caused by mutations in ABCA12, a gene responsible for encoding proteins needed to transport lipids out of cells in the outermost layer of skin [3]. ABCA12 is located on the second chromosome.
This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison