Ichthyosis
Ichthyosis, often referred to as "fish scale disease," is a dry skin condition characterized by varying degrees of skin dryness and scaling. There are two primary types: inherited ichthyosis, which is linked to genetic factors, and acquired ichthyosis, which arises due to underlying medical conditions. Genetic mutations affecting multiple genes can lead to different forms of inherited ichthyosis, including ichthyosis vulgaris, harlequin ichthyosis, and lamellar ichthyosis. Symptoms typically manifest as dry, flaking skin that can resemble fish scales, and may occur on various body parts, most commonly the arms, legs, and trunk. While the severity can range from mild to severe, in extreme cases, symptoms can be disfiguring or life-threatening. There is no cure for ichthyosis, but management focuses on alleviating symptoms through moisturizers and, in some cases, medications. Preventative measures can help reduce the severity of symptoms, such as avoiding harsh soaps and maintaining skin hydration. Understanding ichthyosis is important for those affected and their families, as it highlights the need for ongoing care and support.
Ichthyosis
ALSO KNOWN AS: Fish scale disease; xeroderma
DEFINITION Ichthyosis is a dry skin condition. There are two general types of the condition. Inherited ichthyosis is dryness and scaling of the skin due to hereditary factors; several forms of this condition exist. Acquired ichthyosis is thickening and scaling of the skin that is not inherited but is associated with certain medical disorders.
Risk Factors
Individuals who have family members with ichthyosis are at risk for the condition. Other risk factors include cold weather; frequent or prolonged bathing, especially in hot water; using harsh soaps or detergents; and using soaps or lotions containing certain scents or perfumes.
Etiology and Genetics
Some authorities suggest that mutations in as many as fifteen to twenty different genes can result in different forms of inherited ichthyosis. All are quite rare, but the most common of these are known as ichthyosis vulgaris, harlequin ichthyosis, and lamellar ichthyosis (also known as ichthyosiform erythroderma).
Harlequin ichthyosis results from a mutation in the ABCA12 gene, found on the long arm of chromosome 2 at position 2q34-q35. This gene specifies a protein called the ATP-binding cassette transporter, which functions to transport lipids (fats) in cells that constitute the outermost layer of skin. In the absence of a functional transporter protein, the epidermis develops the hard, thick scales characteristic of the disease.
Lamellar ichthyosis generally results from a mutation in the TGM1 gene, found on the long arm of chromosome 14 (at position 14q11.2). This gene encodes the protein transglutaminase-1, which functions to cross-link structural proteins in the epidermis and to attach specific lipids to epidermal cells. Loss of this protein results in thickening and scaling of the epidermis. Another form of lamellar ichthyosis can result from mutations in either of two adjacent genes on chromosome 17 (at position 17p13.1), known as ALOXE3 and ALOX12B. ALOXE3 specifies an called epoxy alcohol synthase, which functions using the protein product of the ALOX12Bgene as its substrate. There is thus a functional linkage between these two genes, and their products are coexpressed in epidermal cells.
Mutations in the FLG gene, found on chromosome 1 at position 1q21, can lead to the development of ichthyosis vulgaris. Ichthyosis vulgaris was the most common form of the condition, with an estimated prevalence rate of 1 in 100 to 250 people in 2023. This gene encodes the protein profilaggrin, which is subsequently broken down to produce filaggrin, an important structural component of the epidermis.
All these types of ichthyosis are inherited in an autosomal recessive fashion, which means that both copies of the gene must be deficient in order for the individual to be afflicted. Typically, an affected child is born to two unaffected parents, both of whom are carriers of the recessive mutant allele. The probable outcomes for children whose parents are both carriers are 75 percent unaffected and 25 percent affected. If one parent has ichthyosis and the other is a carrier, there is a 50 percent probability that each child will be affected. Some very rare additional types of ichthyosis have been reported to be inherited in an autosomal dominant or in a sex-linked recessive manner.
Symptoms
Ichthyosis can develop on any part of the body, but it most often occurs on the legs, arms, or trunk. The symptoms can vary from mild to severe. In severe cases, the condition may be disfiguring.
Symptoms may include dry, flaking skin; scaling of skin that gives skin the appearance of fish scales; shedding of layers of the skin; and itching of skin. In severe cases, symptoms may include scarring and/or infection due to rubbing and scratching of scales or blisters. With certain rare types of inherited ichthyosis, symptoms appear immediately at birth; are extremely severe, covering the entire body; and cause severe complications or death.
Screening and Diagnosis
The doctor will ask about a patient’s symptoms and medical history and will perform a physical exam. The diagnosis of ichthyosis is usually based on signs and symptoms of the disorder. In rare instances, blood tests or a skin biopsy may be required.
Treatment and Therapy
Since there is no cure for ichthyosis, treatment consists of managing the symptoms. Most treatment is aimed at keeping the skin moist. In severe cases, medication may be prescribed. For the acquired form, treatment that lessens the severity of the underlying noninherited condition may also help lessen the symptoms of the associated ichthyosis.
Many types of moisturizing ointments, lotions, and creams are used to lessen or alleviate symptoms of ichthyosis. These include petroleum jelly; mineral oil; creams, lotions, and ointments containing vitamin A; and a large variety of nonprescription, unscented moisturizers.
For ichthyosis that causes scaling, solutions or creams with lactic or salicylic acid or urea may help. In some cases, doctors may suggest wrapping affected areas with a plastic or cellophane “bandage” after applying a moisturizing agent. Such bandages should not be used on children.
In severe cases, drugs are sometimes prescribed, including etretinate and isotretinoin. These medications are retinoids, which are derivatives of vitamin A; excess amounts of vitamin A can be harmful. Other medications include antibiotics (if the skin becomes infected) and disinfecting soaps, such as chlorhexidine.
Prevention and Outcomes
There are no guidelines for preventing the development of ichthyosis. However, steps to prevent this condition from getting worse include bathing less often; applying nonscented moisturizing agents regularly and frequently, especially in winter; and using only mild soap. Patients should also avoid harsh soaps; soaps with scents or perfumes; skin contact with detergents; and cold, dry weather (when possible).
Bibliography
Beers, Mark H., ed. The Merck Manual of Medical Information. 2d home ed., new and rev. Whitehouse Station, N.J.: Merck Research Laboratories, 2003.
“Disorders of Cornification (Ichthyosis).” In Neonatal Dermatology, edited by Lawrence F. Eichenfield, Ilona J. Frieden, and Nancy B. Esterly. 2d ed. Philadelphia: Saunders Elsevier, 2008.
EBSCO Publishing. Health Library: Ichthyosis. Ipswich, Mass.: Author, 2009. Available through http://www.ebscohost.com.
Joosten, M.D.W. et.al. "New Developments in the Molecular Treatment of Ichthyosis: Review of the Literature." Orphanet Journal of Rare Diseases, vol. 17, no. 269, doi.org/10.1186/s13023-022-02430-6. Accessed 6 Sept. 2024.
Majmundar, Vidit D., and Kalgi Baxi. "Hereditary and Acquired Ichthyosis Vulgaris." StatPearls, 3 Aug. 2023, www.ncbi.nlm.nih.gov/books/NBK562318/. Accessed 6 Sept. 2024.