Steroid Sulfatase Deficiency, Xp22.3 Deletion, FISH
As an aid in the diagnosis of steroid sulfatase deficiency syndrome, in conjunction with CMS / Chromosomes Analysis, for Congenital Disorders, Blood
Detecting cryptic translocations involving Xp22.3 that are not demonstrated by conventional chromosome studies
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Steroid sulfatase deficiency syndrome is associated with a deletion of the STS gene on the short arm of X chromosome (Xp22.3). The syndrome is an X-linked form of ichthyosis, which is a group of cutaneous disorders characterized by increased or abnormal keratinization. The phenotype is variable, with affected males presenting with dry and scaly skin, sparse hair, and conical teeth.
Steroid sulfatase catalyzes the conversion of sulfated steroid precursors to estrogens during pregnancy. Prenatal specimens may be tested in cases where maternal serum screening has identified low or absent levels of unconjugated estriol (UE3). Female relatives of affected males carry the deletion and should be tested if an affected male has been identified.
Fluorescence in situ hybridization (FISH) studies are highly specific and do not exclude other chromosome abnormalities. We recommend that patients suspected of having steroid sulfatase deficiency syndrome also have conventional chromosome studies (CMS / Chromosome Analysis, for Congenital Disorders, Blood) performed to rule out other chromosome abnormalities or translocations.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
An interpretive report will be provided.
Any individual with a normal signal pattern (1 signal on the X homolog) in each metaphase is considered negative for a deletion in the region tested by this probe.
Any patient with a FISH signal pattern indicating loss of the critical region will be reported as having a deletion of the regions tested by this probe.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Because this FISH test is not approved by the FDA, it is important to confirm steroid sulfatase deficiency syndrome diagnoses by other established methods, such as clinical history or physical examination.
FISH analysis was performed on a series of 31 patient specimens (peripheral blood, amniotic fluid, or tissue) and results were compared to cytogenetic or FISH telomere analyses and the patient’s phenotype. In 18 patients with a phenotype consistent with steroid sulfatase deficiency, or a cytogenetic or telomere Xp deletion, this FISH analysis identified an Xp deletion. Four additional patients with chromosomal arrangements involving the X chromosome, but not containing the STS deletion, were also identified. This demonstrated this probe’s ability to define other X chromosome rearrangements in this region that are not consistent with STS. In 9 male patients with a normal karotype or normal FISH telomere analysis results from peripheral blood specimens, no deletions of the STS critical region were identified.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Ballabio A, Zollo M, Carrozzo R, et al: Deletion of the distal short arm of the X chromosome (Xp) in a patient with short stature, chondrodysplasia punctata, and X-linked ichthyosis due to steroid sulfatase deficiency. Am J Med Genet 1991;41:184-187
2. Foote S, Vollrath D, Hilton A, Page DC: The human Y chromosome: overlapping DNA clones spanning the euchromatic region. Science 1992;258:60-66
3. Schnur RE, Trask BJ, van den Engh G, et al: An Xp22 microdeletion associated with ocular albinism and ichthyosis: approximation of breakpoints and estimation of deletion size by using cloned DNA probes and flow cytometry. Am J Hum Genet 1989;45:706-720