X-linked ichthyosis

Other Names

Steroid sulfatase deficiency; SSD; SSDD; Steroid sulfatase deficiency disease; Placental steroid sulfatase deficiency; X linked ichthyosis

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X linked ichthyosis - this boy has an infant brother and maternal uncle with the same affliction

Summary

• X-linked ichthyosis is a disorder in which the skin cells are produced at a normal rate but they do not separate properly at the surface of the stratum corneum (the outermost layer of the skin).
• This slows the rate of shedding of the skin cells, resulting in 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 trunk and back of the neck are more likely to be affected.
• Scales are usually not found on the face, scalp, palms of the hands, and soles of the feet.

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X linked ichthyosis

Genetics

• X-linked ichthyosis is inherited in an X-linked recessive manner.
• X-linked ichthyosis mostly affects males.

Cause

It is usually caused by a mutation or deletion in the STS gene and is inherited in an X-linked recessive manner.

Rare genetic syndromes

In rare cases, the ichthyosis can be part of a genetic syndrome in which other parts of the body are affected.

Symptoms

80%-99% of people have these symptoms

• Dry skin
• Hypohidrosis
• Ichthyosis

30%-79% of people have these symptoms

• Attention deficit hyperactivity disorder

5%-29% of people have these symptoms

• Cryptorchidism
• Neurological speech impairment

Other symptoms

• Abnormality of metabolism/homeostasis
• Ichthyosiform erythroderma
• Neoplasm

Diagnosis

Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Treatment

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.

Genetic counseling issues

Since the majority of cases appear to occur through transmission of an STS deletion from a carrier mother, enzyme testing or DNA testing should be performed in the mother of any newly diagnosed simplex case (i.e. the first case in a family).

In the case of an extended family with many affected individuals, carrier status can often be assigned based on pedigree analysis.

• Males with XLI will transmit the X chromosome harboring the STS deletion or mutation to each of his female offspring, who will therefore be an obligate carrier. However, all male offspring will be unaffected, since they receive their father's Y chromosome.
• Female carriers of an STS deletion or mutation have a 50% chance with each pregnancy of transmitting it to an offspring. Thus, each male offspring has a 50% chance of being affected by XLI, while each female offspring has a 50% chance of being a carrier for this condition. Any individual that inherits the mother's normal copy of the STS gene will be unaffected and will have an extremely low chance of having a child affected with this condition.

Due to random segregation of the chromosomes during gametogenesis, each pregnancy will be subject to the same probabilities, regardless of the number of previously affected or unaffected offspring. The above recurrence risks are based on the assumption that an affected male or carrier female will have children with an unaffected or non-carrier individual. The risks of having affected offspring would clearly increase in the case of a union between a male with XLI and a carrier female.

See also

• Ichthyosis
• Carvajal syndrome