Read more about this disease, some with Classification – Types – Signs and symptoms – Genetics – Pathophysiology – Diagnosis – Screening – Prevention – Treatment and management – Cures and much more, some including pictures and video when available.
X-linked ichthyosis (XLI) is a skin condition caused by the hereditary deficiency of the steroid sulfatase (STS) enzyme that affects 1 in 2000 to 1 in 6000 males.[1] XLI manifests with dry, scaly skin[2] and is due to deletions[3][4] or mutations[5] in the STS gene. XLI and can also occur in the context of larger deletions causing contiguous gene syndromes.[3] Treatment is largely aimed at alleviating the skin symptoms.[6]
In the 1960’z, recessive x-linked ichthyosis was distinguished clinically from other ichthyoses.[7]:486
The major symptoms of XLI include scaling of the skin, particularly on the neck, trunk, and lower extremities. The extensor surfaces are typically the most severely affected areas. The >4 mm diameter scales adhere to the underlying skin and can be dark brown or gray in color. Symptoms may subside during the summer.[1]
XLI can be suspected based on clinical findings, although symptoms can take varying amounts of time to become evident, from a few hours after birth, up to a year in milder cases. The diagnosis is usually made by a dermatologist, who also typically formulates the treatment plan (see below). STS enzyme deficiency is confirmed using a clinically-available biochemical assay. Carrier detection can be performed in mothers of affected sons using this test (see Genetics, below).[8] Molecular testing for DNA deletions or mutations is also offered, and can be particularly useful in the evaluation of individuals with associated medical conditions (see below). Prenatal diagnosis is possible using either biochemical or molecular tests. However, the use of prenatal diagnosis for genetic conditions that are considered to be generally benign raises serious ethical considerations and requires detailed genetic counseling.
The STS gene is located on the X chromosome at band Xp22.3. Thus, the syndrome is an X-linked condition, and it affects males and females differently. The 23rd pair of chromosomes is typically termed the “sex chromosomes”. Females have two X chromosomes and males have one X and one Y chromosome. Therefore, in normal individuals, males carry a single copy of the STS gene and females carry two copies. This gene partially escapes X-inactivation and females normally express higher amounts of the STS enzyme than males.[9]
XLI can occur through new deletions or mutations of the STS gene but is more commonly inherited from a carrier mother.[10] A hemizygous deletion or mutation of the STS gene in a male results in complete absence of enzyme activity, while a female carrier of a mutation or deletion is heterozygous and still has a normal copy of the STS gene. Female carriers of an STS deletion or mutation still express the STS enzyme, although with decreased enzyme activity.[8] For this reason, XLI most commonly affects males, although individuals with numeric abnormalities of the sex chromosomes (45,X and 47,XXY) who also carry STS deletions or mutations would be exceptions to this rule. In addition, a female could be affected if she were the offspring of an affected male and a carrier female and inherited a deletion or mutation of the STS gene on both X chromosomes.
[tubepress mode=’tag’, tagValue=’X-linked ichthyosis’]