Ichthyosis: The Genetics of its Inheritance
Ichthyosis: The Genetics of its Inheritance
Provides a more detailed description of the genetic inheritance patterns of the different forms of ichthyosis.
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Ichthyosis Genetics - The Basics
Ichthyosis is a family of skin conditions that are caused by a genetic mutation.
What are genes?
Genes are pieces of DNA that are “packaged” into chromosomes. You inherit half of your genes from your mother and half from your father. Genes help to determine characteristics such as the color of your eyes and whether your hair is straight or curly.
What’s DNA?
DNA is the basic genetic material of life. It’s found in every cell of your body. It contains the instructions, or genetic code, for making all living things. These instructions are “packaged” into genes.
What are chromosomes?
Chromosomes are rod-shaped structures composed of DNA. Humans normally have 23 pairs of chromosomes. You inherit one chromosome in each pair from your mother and one from your father.
What’s a genetic mutation?
A genetic mutation is a variant or change in DNA. Think of it as a spelling error in the DNA instruction manual. Mutations are common and mostly occur during a person’s life. However, some mutations can be passed from a parent to a child. Some mutations can cause or heighten the likelihood that certain diseases will occur, while others can be protective, lessening the risk. Most genetic mutations, however, have no effect one way or the other on the people who carry them.
How does a genetic mutation cause ichthyosis?
In almost all cases, the genetic mutation or mistake in the gene is passed from parent to child. Remember, you inherit half of your genes from your mother and half from your father. Some types of ichthyosis occur when a single mutated gene is passed from one parent. The parent carrying the mutation has a 50-50 chance of passing it to each of their children. This inheritance pattern – in which just one copy of a mutated gene is needed to cause a disease – is called autosomal dominant.
Other types of ichthyosis occur when a child inherits two copies of the genetic mutation – one from each parent. Each parent has a 50-50 chance of passing the mutation to each of their children . This inheritance pattern – in which it takes two copies of a mutated gene to cause a disease – is known as autosomal recessive.
Many cases of ichthyosis are caused by inheriting two copies of a mutation in a gene called TGM1. This gene carries instructions that enable the outer layer of the skin to form a protective barrier between the body and its environment. When you have two copies of a mutated TGM1 gene, that barrier either fails to form or doesn’t work the way it should. Researchers have identified well over 100 different mutations in the TGM1 gene that can cause ichthyosis.
In very rare cases, a genetic mutation causing ichthyosis can occur spontaneously, without the child inheriting it from one or both parents. This type of mutation is known as a sporadic or de novo mutation.
Sources:
CDC.gov. Genetics Basics. https://www.cdc.gov/genomics/about/basics.htm
González-Del Carmen M, Montaño S, Reyes-Hernández OD, et al. High prevalence of autosomal recessive congenital ichthyosis in a Mexican population caused by a new mutation in the TGM1 gene: epidemiological evidence of a founder effect. Int J Dermatol. 2020;59(8):969-977. doi:10.1111/ijd.14952
Herman ML, Farasat S, Steinbach PJ, et al. Transglutaminase-1 gene mutations in autosomal recessive congenital ichthyosis: summary of mutations (including 23 novel) and modeling of TGase-1. Hum Mutat. 2009;30(4):537-547. doi:10.1002/humu.20952
KidsHealth.org. What Is a Gene? https://kidshealth.org/en/kids/what-is-gene.html
Lee A. 4 beneficial evolutionary mutations that humans are undergoing right now. 2011 Oct 5. https://bigthink.com/surprising-science/evolution-is-still-happening-beneficial-mutations-in-humans/
MedlinePlus What is a gene? https://medlineplus.gov/genetics/understanding/basics/gene/
Melin M, Klar J, Jr Gedde-Dahl T, et al. A founder mutation for ichthyosis prematurity syndrome restricted to 76 kb by haplotype association. J Hum Genet. 2006;51(10):864-871. doi:10.1007/s10038-006-0035-z
Pigg M, Gedde-Dahl T Jr, Cox D, Hausser I, Anton-Lamprecht I, Dahl N. Strong founder effect for a transglutaminase 1 gene mutation in lamellar ichthyosis and congenital ichthyosiform erythroderma from Norway. Eur J Hum Genet. 1998;6(6):589-596. doi:10.1038/sj.ejhg.5200224
This information is provided as a service to patients and parents of patients who have ichthyosis. It is not intended to supplement appropriate medical care, but instead to complement that care with guidance in practical issues facing patients and parents. Neither FIRST, its Board of Directors, Medical & Scientific Advisory Board, Board of Medical Editors, nor Foundation staff and officials endorse any treatments or products reported here. All issues pertaining to the care of patients with ichthyosis should be discussed with a dermatologist experienced in the treatment of their skin disorder.
