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There are many genetic disorders that are sex-linked. X-linked Ichthyosis is an example of a sex-linked genetic skin disorder that generally affects males. The term, “X-linked,” refers to an allele located on an X chromosome and “Ichthys,” from the term “Ichthyosis” (pronounced as ‘ikTHēˈōsəs’), is Greek for “fish.” This genetic disorder is known for causing the surface layer of the skin of an adult male to become rough, dry and patchy like the scales of a fish. Since females have two X chromosomes and males have only one X chromosome and a Y chromosome, they are least likely to express the disease because the normal gene on one of the X chromosomes will mask the trait for the disease on the other whereas in males, since there is only one X chromosome, the trait for the disease will be expressed. The following paragraphs will discuss the causes of X-linked Ichthyosis, explain how it is contracted, state who is particularly at risk for the disorder, list the symptoms, state the consequences if the disorder is not treated, list the treatments that are available for the disorder, and a few other related information on the disorder.
According to the National Institutes of Health (NIH), X-linked Ichthyosis is mainly caused by a mutation or deletion in the steroid sulfatase (STS) gene, resulting in a deficiency in steroid sulfatase. Steroid sulfatase is an enzyme that helps to maintain the integrity of the skin by breaking down and metabolizing a steroid called cholesterol sulfate. The build-up of the cholesterol sulfate steroid in the skin causes the skin cells to strongly adhere to each other more than usual. This prevents the normal shedding of the dead skin cells from happening. The dead skin cells, then, builds up on the surface of the skin and forms clumps that are rough and dry like fish scales.
As mentioned earlier, X-linked Ichthyosis is a genetic, sex-linked, disorder and this disorder is generally passed on from mother to son. It may also be passed on to daughters in an inherited recessive manner. According to the National Organization for Rare Disorders (NORD), males who have X-linked Ichthyosis will pass on the trait of this disease to their daughters but not to their sons. Therefore, females are generally the carriers of this X-linked recessive disorder. In addition, females who are carriers of X-linked Ichthyosis have a 50% chance of passing on the condition to their daughters who will also be carriers of the disorder. For the other half of the time, their sons will be at risk of having the disease. Although it may seem as if X-linked Ichthyosis is a common genetic disorder, it is actually a rare disorder affecting one in 6,000 males according to NORD. The symptoms of this disorder generally appear within the first year an affected individual is born. Given all the information mentioned thus far, the people who are particularly at risk for the disorder are males because this is a sex-linked disorder located on the X chromosome. Since males have only one X chromosome, they do not have a second X chromosome like females to protect them and are, therefore, affected by the disorder.
There are many signs and symptoms of X-linked Ichthyosis. According to the Foundation for Ichthyosis and Related Skin Types (FIRST), the symptoms of X-linked Ichthyosis do not appear when an affected baby is born. The symptoms will however most likely appear any time before the baby turns a year old. Symptoms will include dark scales covering only certain portions of the body, such as the back of the neck, and is commonly distributed symmetrically throughout the body. Other parts of the body, such as the face, scalp, palms, and bottoms of the feet, are generally not affected. According to Anusha Preethi Panthagani, who is a dermatology registrar from DermNet New Zealand and is also the author of “Recessive X-linked Ichthyosis,” scaling is more common on the “extensor surfaces of limbs and the side of the trunk.” In addition, the symptoms normally improve during the summer and, according to the NIH, are generally more severe during the winter. If left untreated, the symptoms could be life-long since it is generally persistent throughout adulthood with or without treatment. Moreover, the life expectancy of an affected individual would still be normal. However, according to the NIH the scaling may also improve with age. In addition to dry skin, other symptoms include decreased ability to sweat (Hypohidrosis), decreased estrogen or delayed progression of giving birth to a child as mentioned by Victor A. McKusick and the contributors of the Online Mendelian Inheritance in Man (OMIM) (a trademark of Johns Hopkins University), low placental steroid sulfatase levels which can cause pregnant mothers to have prolonged labor when giving birth to affected babies, corneal opacities in both the carrier and affected individuals, undescended testicles (cryptorchidism) in affected males, increased risk of testicular cancer, and possible neurological symptoms such as epilepsy, mental retardation, and reduced ability to smell (hyposomia). It is also worth mentioning that about 90% of the affected male individuals experience a deletion of the steroid sulfatase allele. According to OMIM, “Some patients have larger deletions at Xp22.3 that encompasses neighboring genes. These patients may also experience (as mentioned above) mental retardation and Kallmann syndrome…” According to the NIH, Kallmann syndrome is when the stage of puberty in an affected individual is delayed or absent and his/her sense of smell is impaired.
The treatments for X-linked Ichthyosis are generally the same throughout the online resources mentioned in this paper. They include topical treatment such as alpha-hydroxyl acids, lubricating bath oils, and emollients as mentioned by the NIH. According to NORD, this disorder can be treated by applying skin softening creams and lotions which is most effective when the skin is still moist from taking a bath. The topical treatment containing alpha-hydroxyl acids helps to increase the rate of the shedding of dead skin cells or the stratum corneum. The emollients used for treatment generally contain cholesterol, which may also help with the scaling. For affected babies, extra precaution should be taken when using strong topical treatments such as those containing alpha-hydroxyl acids that may sting them and less harsh emollient treatments could be combined with moderate amounts of alpha-hydroxyl acids. According to Panthagani, some patients may not require treatments. However, Panthagani mentions additional treatment options such as rubbing the scales with a pumice stone or exfoliating sponge to remove it, using agents in topical keratolytics such as lactic acid, glycolic acid, salicylic acid, and urea to improve skin appearance and aid in the peeling of the skin (desquamation), topical isotretinoin, and topical tazarotene which is a receptor-selective retinoid. Furthermore, Panthagani mentions how there is ongoing research to determine whether or not affected individuals may be treated with gene transfer and also how affected males should regularly self-perform testicular check-ups.
According to FIRST, there are many other types of Ichthyosis and X-linked Ichthyosis is just one of the five main types. Other types of Ichthyosis include lamellar Ichthyosis, congenital ichthyosiform erythroderma, Ichthyosis vulgaris, and epidermolyic Ichthyosis. As mentioned earlier, X-linked Ichthyosis is less common and can be severe or mild. The main difference between X-linked Ichthyosis and other types of Ichthyosis is that it is sex-linked. Congenital Ichthyosiform Erythroderma (CIE) or Autosomal Recessive Congenital Ichthyosis is rarer than X-linked Ichthyosis and is characterized by really small light-colored scales, red skin, and the thickening of the palms, soles, and flexures. The symptoms of CIE often appear at birth as a collodion parchment-like membrane that covers the entire skin surface of the baby and cracks before or after birth. On the other hand, Ichthyosis Vulgaris is the most common type of Ichthyosis and people who are usually affected by it usually do not know that they are because they it just gets dismissed as having “dry skin.” Just like X-linked Ichthyosis, Ichthyosis Vulgaris is characterized by the build-up of scale. However, the difference between these two conditions is that the scales of Ichthyosis Vulgaris are usually very small and white and are more severe at the lower legs than the neck. The treatments for all of these types of Ichthyosis are generally the same—with lotions and topical treatments containing alpha-hydroxyl acids.
In conclusion, X-linked Ichthyosis is a human genetic disorder that is sex-linked and commonly found in males. It is caused by the deletion of an allele on the X chromosome that code for steroid sulfatase, an enzyme that helps break down the cholesterol sulfate steroid that builds up on the skin and prevents the dead skin cells from peeling off. It is a rare skin disease that can be persistent throughout an affected individual’s life, regardless of whether it is treated. Males are particularly at risk for this disorder because females, even though the disorder may be transmitted to them, are only carriers of the gene and are protected by the other X chromosome that is not affected by the mutation/deletion. Symptoms include dry, scaly skin, low estrogen levels and prolonged child birth in pregnant women, and several potential neurological effects such as mental retardation and the inability to smell that may arise if an affected individual also experienced the deletion of neighboring genes other than the one coding for steroid sulfatase. Treatments are generally topical and include lotions, creams, and emollients that contain agents which help reduce the dark scales commonly seen with this skin disorder. They may be only temporary unless the patient undergoes a gene transfer or the scaling improves over time. X-linked Ichthyosis is not the only skin disease that is linked to the scaling of the epidermis. There are other types of Ichthyosis such as Ichthyosis Vulgaris which have different causes and symptoms. It is interesting that disorders like X-linked Ichthyosis can coexist with other disorders within a patient.
- “Collodion Baby | Foundation for Ichthyosis & Related Skin Types (FIRST).” First Skin Foundation, www.firstskinfoundation.org/content.cfm/category_id/741/page_id/543.
- “Definition of Ichthyosis.” MedicineNet, www.medicinenet.com/script/main/art.asp?articlekey=10133.
- “Ichthyosis Vulgaris.” First Skin Foundation, www.firstskinfoundation.org/types-of-Ichthyosis/Ichthyosis-Vulgaris.
- “Ichthyosis, X Linked.” NORD (National Organization for Rare Disorders), rarediseases.org/rare-diseases/ichthyosis-x-linked/.
- “Kallmann Syndrome – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, ghr.nlm.nih.gov/condition/kallmann-syndrome.
- Malik, Amna et al. “X-linked ichthyosis associated with psychosis and behavioral abnormalities: a case report” Journal of medical case reports vol. 11,1 267. 22 Sep. 2017, doi:10.1186/s13256-017-1420-2
- McKusick, Victor A. “ICHTHYOSIS, X-LINKED; XLI.” Edited by Cassandra L. Kniffin, Www.omim.org, Johns Hopkins University, 4 Sept. 2018, www.omim.org/entry/308100.
- Panthagani, Anusha Preethi. “Recessive X-Linked Ichthyosis.” Edited by Amanda Oakley, Peutz-Jeghers Syndrome | DermNet New Zealand, Sept. 2015, www.dermnetnz.org/topics/recessive-x-linked-ichthyosis/.
- “STS Gene – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, ghr.nlm.nih.gov/gene/STS.
- “X-Linked Ichthyosis.” First Skin Foundation, www.firstskinfoundation.org/types-of-Ichthyosis/X-linked-Ichthyosis/?gclid=Cj0KCQiAxZPgBRCmARIsAOrTHSb2K-Fxnye668CZpt716_nlWWmuyuUTD2cJ2djHHZmS2v1A3XOroNYaAmeYEALw_wcB.
- “X-Linked Ichthyosis.” Genetic and Rare Diseases Information Center, U.S. Department of Health and Human Services, rarediseases.info.nih.gov/diseases/7904/x-linked-ichthyosis.
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