What is X-Linked Ichthyosis?
X-linked ichthyosis is a genetic disorder caused by a mutation in the enzyme steroid sulfatase (STS). STS is involved in the metabolism of cholesterol sulfate (CSO4), needed for development of a healthy stratum corneum. X-linked ichthyosis mostly affects males. It is usually caused by a mutation or deletion in the STS gene and is inherited in an X-linked recessive manner. In rare cases, the ichthyosis can be part of a genetic syndrome in which other parts of the body are affected. Clinically, patients develop hyperkeratosis along with skin barrier dysfunction. Approximately 90% of patients with X-linked ichthyosis have complete or partial deletions of the STS gene. No evidence of genotypic-phenotypic correlation has been shown, regardless of the location or type of the STS mutation. X-linked ichthyosis is the second most common type of ichthyosis and one of the most frequent human enzyme deficiency disorders.
X-linked ichthyosis is considered one of the five main types of ichthyosis (the others being lamellar ichthyosis, congenital ichthyosiform erythroderma, ichthyosis vulgaris and epidermolytic ichthyosis (formerly epidermolytic hyperkeratosis)). X-linked ichthyosis is less common, can range from mild to severe, and occurs only in males.
In X-linked ichthyosis, the skin cells are produced at a normal rate but they do not separate normally at the surface of the stratum corneum (the outermost layer of the skin), and are not shed as quickly as they should be. The result is a build-up of scales. The scales of X-linked ichthyosis are often dark and usually cover only a portion of the body. Typically, the face, scalp, palms of the hands, and soles of the feet are free from scales, while the back of the neck is almost always affected. X-linked ichthyosis frequently improves in the summer. Babies with X-linked ichthyosis often appear normal when they are born, but the skin abnormalities will almost always show up by their first birthday.
How common is X-Linked Ichthyosis？
RXLI affects almost exclusively males. It is the second most common type of ichthyosis with an estimated prevalence of 1/2,000 to 1/6,000 males. In the mainland China, an estimated 1 in 500 people are carriers of a genetic mutation that causes X-Linked Ichthyosis.
How is X-Linked Ichthyosis treated?
Topical treatment may consist of alpha-hydroxy acids, lubricating bath oils, and emollients. For adult patients, systemic retinoids may be an option, especially during winter when the ichthyosis is often more severe. The ichthyosis is life-long, but the scaling may improve with age.