Prenatal Diagnosis and Testing for X-Linked Ichthyosis

Low estriol levels detected in prenatal screenings can be a marker for X-linked ichthyosis. Ichthyosis is a family of rare genetic skin diseases, characterized by thick, dry, cracked, and scaling skin. The genetic defect in X-linked ichthyosis causes a deficiency of the enzyme steroid sulfatase. X-linked ichthyosis is considered one of the more mild forms of ichthyosis and is treatable with topical creams and lotions. Children with X-linked ichthyosis often appear normal at birth. Several days following birth the skin typically peels and flakes in an exaggeration of the normal pattern of neonatal desquamation. Afterward, dry flaky scales are usually present on the trunk and arms and legs. The symptoms of this form of ichthyosis are largely limited to the skin; that is X-linked ichthyosis does not cause neurological or developmental impairments. However, there is an increased incidence of cryptorchidism (failure of the testes to descend from the abdomen to the scrotum during development. 

Fluorescent In Situ Hybridization (FISH) testing for steroid sulfatase gene deletion can confirm X-linked ichthyosis in the suspected fetus. However, FISH testing can miss up to 10% of individuals with X-linked ichthyosis. If the FISH is negative, and the index of clinical suspicions is high for X-linked ichthyosis (i.e., family history or affected sibling), further testing in the form of an enzyme assay for steroid sulfatase activity is indicated. Both the FISH analysis and the enzyme analysis can be performed on amniotic fluid or a chorionic villus sample.
 
A national listing of the laboratories that perform FISH testing or steroid sulfatase enzyme assays are found in the Foundation brochure “Testing for X-linked Ichthyosis.”
 
A listing is also available on the website, www.genetests.org.

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