Ichthyosis, X Linked

Disease Overview

X-linked ichthyosis is a genetic skin disorder that affects males. It is an inborn error of metabolism characterized by a deficiency of the enzyme steroid sulfatase. Under normal conditions, this enzyme breaks down (metabolizes) cholesterol sulfate, a member of the chemical family of steroids. Cholesterol sulfate plays a role in maintaining the integrity of the skin. If steroid metabolism is interrupted and cholesterol sulfate accumulates in the skin cells, the skin cells stick together more strongly than usual. The normal shedding of dead skin cells is inhibited and the skin cells build up and clump into scales.

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Synonyms

• Placental Steroid Sulfatase Deficiency; STS
• Recessive X-linked Ichthyosis
• Steroid Sulfatase Deficiency
• Steroid Sulfatase Deficiency Disease; SSDD

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Signs & Symptoms

Boys with X-linked ichthyosis appear normal at birth. The skin symptoms generally appear within the first year of life. Brownish scales that adhere to the skin are among the first signs of the disorder. The back and legs are most frequently involved early. The face, scalp, palms and soles, and hollows of the elbows and knees are usually spared.

In about half of adult males, comma-shaped corneal opacities occur in the eyes (seen on exam by an ophthalmologist), but they do not interfere with vision. Symptoms can improve markedly in the summer months and warm humid climates.

A small percentage of males may experience undescended testes (crytpchordism). These men may be at increased risk for contracting malignancies of the testes.

Women who are carriers of X-linked ichthyosis and give birth to sons with the disorder may experience a delay in labor or failure of labor to initiate. The enzyme defect can cause a decrease in production of maternal estriol in late pregnancy, which may affect labor and delivery. Low serum estriol levels detected by prenatal screening suggest the presence of a fetus with X-linked ichthyosis.

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Causes

X-linked recessive disorders are conditions that are coded on the X chromosome. Females have two X chromosomes; males have one X chromosome and one Y chromosome. Therefore, in females, the normal gene on one X chromosome can mask disease traits on the other X chromosome. Since males have only one X chromosome, if they inherit the gene for a disease present on the X they will express the disease. Men with X-linked disorders transmit the gene to all their daughters, who are carriers, but never to their sons. Women who are carriers of an X-linked disorder have a 50 percent chance of transmitting the carrier condition to their daughters and a 50 percent risk of transmitting the disease to their sons.

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Affected populations

X-linked ichthyosis is a rare disorder affecting one in 6,000 males.

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Disorders with Similar Symptoms

Symptoms of the following disorders may be similar to those of X-linked ichthyosis. Comparisons can be useful for a differential diagnosis.

“Ichthyoses” or “disorders of cornification” are general terms describing a group of scaly skin disorders. They are characterized by an abnormal accumulation of large amounts of dead skin cells (squames) in the top layer of the skin. The conversion of an abnormally large number of epidermal cells into squamous cells is thought to be caused by a defect in the metabolism of the skin cells known as “corneocytes” or the fat-rich matrix around these cells. These cells can be thought of as bricks, while the matrix would be the mortar holding these cells together. (See “Ichthyosis” in the Rare Disease Database.)

Ichthyosis congenita (collodion baby; congenital ichthyosiform erythroderma; xeroderma; desquamation of the newborn) is an inherited skin disorder. It is characterized by generalized, abnormally red, dry, and rough skin with large coarse and fine white scales. Itchiness (pruritus) usually also develops. Skin on the palms of the hands and soles of the feet can be abnormally thick. (For more information, choose “Ichthyosis Congenita” as your search term in the Rare Disease Database.)

Other forms of ichthyosis include Sjogren-Larsson syndrome, Netherton syndrome, ichthyosis hystrix, lamellar ichthyosis, Darier disease, and epidermolytic hyperkeratosis. (Search under each name for more information on that disorder in the Rare Disease Database.)

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Standard Therapies

X-linked ichthyosis can be diagnosed before birth by amniocentesis or chorionic villus sampling. Low maternal estriol levels can suggest the presence of X-linked ichthyosis.

X-linked ichthyosis is treated by applying skin softening creams and lotions. This can be especially effective after bathing while the skin is still moist. X-linked ichthyosis responds relatively well to topical treatment with alpha-hydroxy acids, which accelerate the shedding of the dead skin cells. Cholesterol containing emollients may also improve the scaling. Alpha-hydroxy acids may sting the skin of babies and young children and should be used cautiously or in combination with another mild emollient product.

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Clinical Trials and Studies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010

Email: [email protected]

For information about clinical trials sponsored by private sources, contact:

www.centerwatch.com

Oral retinoids, drugs derived from vitamin A, can be effective against some forms of ichthyosis. However, X-linked ichthyosis is not considered severe enough to warrant the use of oral retinoids.

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References

JOURNAL ARTICLES

Elias, PM, Williams, ML. Enlightened Therapy of the Disorders of Cornification. Clinics in Dermatology. 2003; 21: 269 / 273.

DiGiovanna, JJ, Robinson-Bostom, L. Ichthyosis: etiology, diagnosis, and management. Am J Clin Dermatol. 2003;4: 81-95.

Zettersen, E, Man, MQ, Sato, J, et al. Recessive x-linked ichthyosis: role of cholesterol sulfate accumulation in the barrier abnormality. J Invest Dermatol. 1998; 111: 784-90.

Williams, ML, et al. Genetically Transmitted, Generalized Disorders of Cornification. The Ichthyoses. Dermatol Clin. January 1987; 5(1): 155-78.

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Programs & Resources

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